RMS measurement of high crest-factor signals
Dual-channel and channel difference outputs ports
Integrated accurately scaled temperature sensor
Wide dynamic range ±1 dB over 60 dB
±0.5 dB temperature-stable linear-in-dB response
Low log conformance ripple
+5 V operation at 70 mA, –40°C to +85°C
Small footprint, 5 mm x 5 mm, LFCSP
APPLICATIONS
Wireless infrastructure power amplifier linearization/control
Antenna VSWR monitor
Gain and power control and measurement
Transmitter signal strength indication (TSSI)
Dual-channel wireless infrastructure radios
GENERAL DESCRIPTION
The AD8364 is a true rms, responding, dual-channel RF power
measurement subsystem for the precise measurement and control
of signal power. The flexibility of the AD8364 allows communications systems, such as RF power amplifiers and radio transceiver
AGC circuits, to be monitored and controlled with ease. Operating
on a single 5 V supply, each channel is fully specified for operation
up to 2.7 GHz over a dynamic range of 60 dB. The AD8364
provides accurately scaled, independent, rms outputs of both RF
measurement channels. Difference output ports, which measure
the difference between the two channels, are also available. The
on-chip channel matching makes the rms channel difference
outputs extremely stable with temperature and process variations.
The device also includes a useful temperature sensor with an
accurately scaled voltage proportional to temperature, specified
over the device operating temperature range. The AD8364 can
be used with input signals having rms values from −55 dBm to
+5 dBm referred to 50 Ω and large crest factors with no
accuracy degradation.
Dual 60 dB TruPwr™ Detector
AD8364
FUNCTIONAL BLOCK DIAGRAM
VPSA
INHA
INLA
PWDN
OMR
INLB
INHB
VPSB
CHPA
DECA
24232221201918 17
TEMP
25
26
27
28
29
30
31
32
CHANNEL A
TruPwr™
OUTA
OUTB
CHANNEL B
TruPwr™
BIAS
12345678
DECB
CHPB
COM
I
SIG
I
TGT
I
SIG
I
TGT
VGA
CONTROL
COMB
VPSR
VGA
CONTROL
2
2
2
2
ADJB
ACO
ADJA
TEMP
VREF
Figure 1. Functional Block Diagram
Integrated in the AD8364 are two matched AD8362 channels
AD8362 data sheet for more information) with improved
(see the
temperature performance and reduced log conformance ripple.
Enhancements include improved temperature performance and
reduced log-conformance ripple compared to the
chip wide bandwidth output op amps are connected to accommodate flexible configurations that support many system
solutions.
The device can easily be configured to provide four rms
measurements simultaneously. Linear-in-dB rms measurements
are supplied at OUTA and OUTB, with conveniently scaled
slopes of 50 mV/dB. The rms difference between OUTA and
OUTB is available as differential or single-ended signals at
OUTP and OUTN. An optional voltage applied to VLVL
provides a common mode reference level to offset OUTP and
OUTN above ground.
The AD8364 is supplied in a 32-lead, 5 mm × 5 mm LFCSP, for
the operating temperature of –40°C to +85°C.
ACO
VLVL
CLPA
16
15
14
13
12
11
10
9
CLPB
AD8362. On-
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
05334-001
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable.
However, no responsibility is assumed by Analog Devices for its use, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. No license is granted by implication
or otherwise under any patent or patent rights of Analog Devices. Trademarks and
registered trademarks are the property of their respective owners.
Specified Frequency Range LF 2.7 GHz
DC Common-Mode Voltage 2.5 V
Signal Output Interface OUT[A, B] (Pins 15, 10)
Wideband Noise CLP[A, B] = 0.1µF, f
RF input = 2140 MHz, ≥−40 dBm
MEASUREMENT MODE,
450 MHz OPERATION
ADJA = ADJB = 0 V, error referred to best fit line using
linear regression @ P
T
= 25°C, balun = M/A-Com ETK4-2T
A
±1 dB Dynamic Range1 Pins OUT[A, B] 69 dB
−40°C < TA < +85°C 65 dB
±0.5 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 62/59 dB
−40°C < TA < +85°C, (Channel A/Channel B) 50/52 dB
Maximum Input Level ±1 dB error 12 dBm
Minimum Input Level ±1 dB error −58 dBm
Slope 51.6 mV/dB
Intercept −59 dBm
Output Voltage—High Power In Pins OUT[A, B] @ P
Output Voltage—Low Power In Pins OUT[A, B] @ P
Temperature Sensitivity Deviation from OUT[A, B] @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Deviation from OUTP to OUTN @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Input A to Input B Isolation Baluns = Macom ETC1.6-4-2-3 (both channels) 71 dB
Input A to OUTB Isolation Freq separation = 1 kHz
Input B to OUTA Isolation2 P
P
= −50 dBm, OUTB = OUTB
INHB
= −50 dBm, OUTA = OUTA
INHA
Input Impedance INHA/INLA, INHB/INLB differential drive 210||0.1 Ω||pF
Input Return Loss With recommended balun −12 dB
MEASUREMENT MODE,
880 MHz OPERATION
ADJA = ADJB = 0 V, error referred to best fit line using
linear regression @ P
= 25°C, balun = Mini-Circuits® JTX-4-10T
T
A
±1 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 66/57 dB
−40°C < TA < +85°C 58/40 dB
±0.5 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 62/54 dB
−40°C < TA < +85°C 20/20 dB
Maximum Input Level ±1 dB error, (Channel A/Channel B) 8/0 dBm
Minimum Input Level ±1 dB error, (Channel A/Channel B) −58/−57 dBm
Slope 51.6 mV/dB
Intercept −59.2 dBm
Output Voltage—High Power In Pins OUT[A, B] @ P
Output Voltage—Low Power In Pins OUT[A, B] @ P
= 100 kHz,
SPOT
40 nV/√Hz
= −40 dBm and −20 dBm,
INH[A, B]
= −10 dBm 2.53 V
INH[A, B]
= −40 dBm 0.99 V
INH[A, B]
= −10 dBm −0.1, +0.2 dB
INH[A, B]
= −25 dBm −0.2, +0.3 dB
INH[A, B]
= −40 dBm −0.3, +0.4 dB
INH[A, B]
= −10 dBm, −25 dBm ±0.25 dB
INH[A, B]
= −25 dBm, −25 dBm ±0.2 dB
INH[A, B]
= −40 dBm, −25 dBm ±0.2 dB
INH[A, B]
± 1 dB 54 dB
PINHB
± 1 dB 54 dB
PINHA
= −40 dBm and −20 dBm,
INH[A, B]
= −10 dBm 2.54 V
INH[A, B]
= −40 dBm 0.99 V
INH[A, B]
Rev. 0 | Page 3 of 48
Page 4
AD8364
Parameter Conditions Min Typ Max Unit
Temperature Sensitivity Deviation from OUT[A, B] @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Deviation from OUTP to OUTN @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Input A to Input B Isolation Baluns = Macom ETC1.6-4-2-3 (both channels) 64 dB
Input A to OUTB Isolation P
Input B to OUTA Isolation2 P
= −50 dBm, OUTB = OUTB
INHB
= −50 dBm, OUTA = OUTA
INHA
Input Impedance INHA/INLA, INHB/INLB differential drive 200||0.3 Ω||pF
Input Return Loss With recommended balun −9 dB
MEASUREMENT MODE,
1880 MHz OPERATION
ADJA = ADJB = 0.75 V, error referred to best fit line using
linear regression @ P
T
= 25°C, balun = Murata LDB181G8820C-110
A
±1 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 69/61 dB
−40°C < TA < +85°C 60/50 dB
±0.5 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 62/51 dB
−40°C < TA < +85°C 58/51 dB
Maximum Input Level ±1 dB error, (Channel A/Channel B) 11/3 dBm
Minimum Input Level ±1 dB error −58 dBm
Slope 50 mV/dB
Intercept −62 dBm
Output Voltage—High Power In Pins OUT[A, B] @ P
Output Voltage—Low Power In Pins OUT[A, B] @ P
Temperature Sensitivity Deviation from OUT[A, B] @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Deviation from OUTP to OUTN @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Input A to Input B Isolation Baluns = Macom ETC1.6-4-2-3 (both channels) 61 dB
Input A to OUTB Isolation P
Input B to OUTA Isolation2 P
= −50 dBm, OUTB = OUTB
INHB
= −50 dBm, OUTA = OUTA
INHA
Input Impedance INHA/INLA, INHB/INLB differential drive 167||0.14 Ω||pF
Input Return Loss With recommended balun −8 dB
MEASUREMENT MODE,
2.14 GHz OPERATION
ADJA = ADJB = 1.02 V, error referred to best fit line using
linear regression @ P
T
= 25°C, balun = Murata LDB212G1020C-001
A
±1 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 66/57 dB
−40°C < TA < +85°C 58/40 dB
±0.5 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 62/54 dB
−40°C < TA < +85°C 30/30 dB
Maximum Input Level ±1 dB Error, (Channel A/Channel B) −2/−4 dBm
Minimum Input Level ±1 dB Error, (Channel A/Channel B) −57−51 dBm
Slope Channel A/Channel B 49.5/52.1 mV/dB
Intercept Channel A/Channel B −58.3/−57.1 dBm
Output Voltage—High Power In Pins OUT[A, B] @ P
= −10 dBm +0.5 dB
INH[A, B]
= −25 dBm +0.5 dB
INH[A, B]
= −40 dBm +0.5 dB
INH[A, B]
= −10 dBm, −25 dBm +0.1, −0.2 dB
INH[A, B]
= −25 dBm, −25 dBm +0.1, −0.2 dB
INH[A, B]
= −40 dBm, −25 dBm +0.1, −0.2 dB
INH[A, B]
± 1 dB 35 dB
PINHB
± 1 dB 35 dB
PINHA
= −40 dBm and −20 dBm,
INH[A, B]
= −10 dBm 2.49 V
INH[A,B]
= −40 dBm 0.98 V
INH[A,B]
= −10 dBm +0.5, −0.2 dB
INH[A, B]
= −25 dBm +0.5, −0.2 dB
INH[A, B]
= −40 dBm +0.5, −0.2 dB
INH[A, B]
= −10 dBm, −25 dBm ±0.3 dB
INH[A, B]
= −25 dBm, −25 dBm ±0.3 dB
INH[A, B]
= −40 dBm, −25 dBm ±0.3 dB
INH[A, B]
± 1 dB 33 dB
PINHB
± 1 dB 33 dB
PINHA
= −40 dBm and −20 dBm,
INH[A, B]
= −10 dBm 2.42 V
INH[A, B]
Rev. 0 | Page 4 of 48
Page 5
AD8364
Parameter Conditions Min Typ Max Unit
Output Voltage—Low Power In Pins OUT[A, B] @ P
Temperature Sensitivity Deviation from OUT[A, B] @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Deviation from OUTP to OUTN @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Deviation from CW Response 5.5 dB peak-to-rms ratio (WCDMA one channel) 0.2 dB
12 dB peak-to-rms ratio (WCDMA three channels) 0.3 dB
18 dB peak-to-rms ratio (WCDMA four channels) 0.3 dB
Input A to Input B Isolation Baluns = Macom ETC1.6-4-2-3 (both channels) 58 dB
Input A to OUTB Isolation P
Input B to OUTA Isolation2 P
= −50 dBm, OUTB = OUTB
INHB
= −50 dBm, OUTA = OUTA
INHA
Input Impedance INHA/INLA, INHB/INLB differential drive 150||1.9 Ω||pF
Input Return Loss With recommended balun −10 dB
MEASUREMENT MODE,
2.5 GHz OPERATION
ADJA = ADJB = 1.14 V, error referred to best fit line using
linear regression @ P
T
= 25°C, balun = Murata LDB182G4520C-110
A
± 1 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 69/63 dB
−40°C < TA < +85°C 58 dB
±0.5 dB Dynamic Range1 Pins OUT[A, B], (Channel A/Channel B) 55/50 dB
−40°C < TA < +85°C 25 dB
Maximum Input Level ±1 dB error, (Channel A/Channel B) 17/11 dBm
Minimum Input Level ±1 dB error −52 dBm
Slope 50 mV/dB
Intercept −52.7 dBm
Output Voltage—High Power In Pins OUT[A, B] @ P
Output Voltage—Low Power In Pins OUT[A, B] @ P
Temperature Sensitivity Deviation from OUT[A, B] @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Deviation from OUTP to OUTN @ 25°C
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
−40°C < TA < 85°C; P
Input A to Input B Isolation Baluns = Macom ETC1.6-4-2-3 (both channels) 54 dB
Input A to OUTB Isolation P
Input B to OUTA Isolation2 P
= −50 dBm, OUTB = OUTB
INHB
= −50 dBm, OUTA = OUTA
INHA
Input Impedance INHA/INLA, INHB/INLB differential drive 150||1.7 Ω||pF
Input Return Loss With recommended balun −11.5 dB
OUTPUT INTERFACE Pin OUTA and OUTB
Voltage Range Min RL ≥ 200 Ω to ground 0.09 V
Voltage Range Max RL ≥ 200 Ω to ground VS − 0.15 V
Source/Sink Current OUTA and OUTB held at VS/2, to 1% change 70 mA
= −40 dBm 0.90 V
INH[A, B]
= −10 dBm +0.1, −0.4 dB
INH[A, B]
= −25 dBm +0.1, −0.4 dB
INH[A, B]
= −40 dBm +0.1, −0.4 dB
INH[A, B]
= −10 dBm, −25 dBm +0.1, −0.4 dB
INH[A, B]
= −25 dBm, −25 dBm +0.2, −0.2 dB
INH[A, B]
= −40 dBm, −25 dBm +0.1, −0.2 dB
INH[A, B]
± 1 dB 33 dB
PINHB
± 1 dB 33 dB
PINHA
= −40 dBm and −20 dBm,
INH[A, B]
= −10 dBm 2.14 V
INH[A, B]
= −40 dBm 0.65 V
INH[A, B]
= −10 dBm ±0.5 dB
INH[A, B]
= −25 dBm ±0.5 dB
INH[A, B]
= −40 dBm ±0.5 dB
INH[A, B]
= −10 dBm, −25 dBm ±0.3 dB
INH[A, B]
= −25 dBm, −25 dBm ±0.3 dB
INH[A, B]
= −40 dBm, −25 dBm ±0.3 dB
INH[A, B]
± 1 dB 31 dB
PINHB
± 1 dB 31
PINHA
Rev. 0 | Page 5 of 48
Page 6
AD8364
Parameter Conditions Min Typ Max Unit
SETPOINT INPUT Pin VSTA and VSTB
Voltage Range Law conformance error ≤1 dB 0.5 3.75 V
Input Resistance 68 kΩ
Logarithmic Scale Factor f = 450 MHz, −40°C ≤ TA ≤ +85°C 50 mV/dB
Logarithmic Intercept f = 450 MHz, −40°C ≤ TA ≤ +85°C, referred to 50 Ω −55 dBm
CHANNEL DIFFERENCE OUTPUT Pin OUTP and OUTN
Voltage Range Min RL ≥ 200 Ω to ground 0.1 V
Voltage Range Max RL ≥ 200 Ω to ground VS − 0.15 V
Source/Sink Current OUTP and OUTN held at VS/2, to 1% change 70 mA
DIFFERENCE LEVEL ADJUST Pin VLVL
Voltage Range3 OUT[P, N] = FBK[A, B] 0 5 V
OUT[P,N] Voltage Range OUT[P, N] = FBK[A, B] 0
V
S
0.15
Input Resistance 1 kΩ
TEMPERATURE COMPENSATION Pin ADJA and ADJB
Input Voltage Range 0 2.5 V
Input Resistance >1 MΩ
VOLTAGE REFERENCE Pin VREF
Output Voltage RF in = −55 dBm 2.5 V
Temperature Sensitivity −40°C ≤ TA ≤ +85°C 0.4 mV/°C
Current Limit Source/Sink 1% change 10/3 mA
TEMPERATURE REFERENCE Pin TEMP
Output Voltage TA = 25°C, RL ≥ 10 kΩ 0.62 V
Temperature Coefficient −40°C ≤ TA ≤ +85°C, RL ≥ 10 kΩ 2 mV/°C
Current Source/Sink TA = 25°C to 1% change 1.6/2 mA
POWER-DOWN INTERFACE Pin PWDN
Logic Level to Enable Logic LO enables 1 V
Logic Level to Disable Logic HI disables 3 V
Input Current Logic HI PWDN = 5 V 95 µA
Logic LO PWDN = 0 V <100 µA
Enable Time
Disable Time
PWDN LO to OUTA/OUTB at 100% final value,
C
LPA/B
= Open, C
= 10 nF, RF in = 0 dBm
HPA/B
PWDN HI to OUTA/OUTB at 10% final value,
C
LPA/B
= Open, C
= 10nF, RF in = 0 dBm
HPA/B
2 µs
1.6 µs
POWER INTERFACE Pin VPS[A, B], VPSR
Supply Voltage 4.5 5.5 V
Quiescent Current RF in = −55 dBm, VS = 5 V 70 mA
−40°C ≤ TA ≤ +85°C 90 mA
Supply Current PWDN enabled, VS = 5 V 500 µA
−40°C ≤ TA ≤ +85°C 900 µA
1
Best fit line, linear regression.
2
See for a plot of isolation vs. frequency for a ±1 dB error. Figure 75
3
VLVL + OUTA/2 should not exceed VPSA − 1.31 V. Likewise, VLVL + OUTB/2 should not exceed VPSB − 1.31 V.
−
V
Rev. 0 | Page 6 of 48
Page 7
AD8364
ABSOLUTE MAXIMUM RATINGS
Table 2.
Parameter Rating
Supply Voltage VPSA, VPSB, VPSR 5.5 V
PWDN, VSTA, VSTB, ADJA, ADJB,
0 V, 5.5 V
FBKA, FBKB
Input Power (Referred to 50 Ω) 23 dBm
Internal Power Dissipation 600 mW
θJA 39.8°C/W
1, 2
θJC 3.9°C/W2
θJB 22.8°C/W2
ΨJT 0.4°C/W
1, 2
Maximum Junction Temperature 125°C
Operating Temperature Range −40°C to +85°C
Storage Temperature Range −65°C to +150°C
1
Still air.
2
All values are modeled using a standard 4-layer JEDEC test board with the
pad soldered to the board and thermal vias in the board.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on
the human body and test equipment and can discharge without detection. Although this product features
proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy
electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance
degradation or loss of functionality.
Rev. 0 | Page 7 of 48
Page 8
AD8364
M
M
A
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
VPSA
INHA
INLA
PWDN
COMR
INLB
INHB
VPSB
25
26
27
28
29
30
31
32
CHPA
COM
DECA
24
23222120191817
AD8364
TOP VIEW
PIN 1
INDICATOR
12345
DECB
CHPB
COMB
ACO
VPSR
ADJA
ADJB
ACO
TEMP
678
VLVL
VREF
CLPA
VSTA
16
OUTA
15
FBKA
14
OUTP
13
OUTN
12
FBKB
11
OUTB
10
VSTB
9
CLPB
05334-002
Figure 2. Pin Configuration
Table 3. Pin Function Descriptions
Pin No. Mnemonic Description Equiv. Circuit
1 CHPB Connect to common via a capacitor to determine 3 dB point of Channel B input signal high-
pass filter.
2, 23 DECB, DECA Decoupling Terminals for INHA/INLA and INHB/INLB. Connect to common via a large
capacitance to complete input circuit.
3, 22, 29 COMB, COMA, COMR Input System Common Connection. Connect via low impedance to system common.
4, 5 ADJB, ADJA Temperature Compensation for Channel B and Channel A. An external voltage is connected
to these pins to improve temperature drift. This voltage can be derived from VREF, that is,
connect a resistor from VREF to ADJ[A, B] and another resistor from ADJ[A, B] to ground. The
value of these resistors change as the frequency changes.
6 VREF General-Purpose Reference Voltage Output of 2.5 V.
7 VLVL Reference Level Input for OUTP and OUTN. (Usually connected to VREF through a voltage
divider or left open).
8, 17 CLPB, CLPA Channel B and Channel A Connection for Loop Filter Integration (Averaging) Capacitor.
Connect a ground-referenced capacitor to this pin. A resistor can be connected in series with
this capacitor to improve loop stability and response time.
9 VSTB The voltage applied to this pin sets the decibel value of the required RF input voltage to
Channel B that results in zero current flow in the loop integrating capacitor pin, CLPB.
10 OUTB Channel B Output of Error Amplifier. In measurement mode, normally connected directly to
VSTB.
11 FBKB Feedback Through 1 kΩ to the Negative Terminal of the Integrated Op Amp Driving OUTN.
12 OUTN Channel Differencing Op Amp Output. In measurement mode, normally connected directly to
FBKB and follows the equation OUTN = OUTA − OUTB + VLVL.
13 OUTP Channel Differencing Op Amp Output. In measurement mode, normally connected directly to
FBKA and follows the equation OUTP = OUTA − OUTB + VLVL.
14 FBKA Feedback Through 1kΩ to the Negative Terminal of the Integrated Op Amp Driving OUTP.
15 OUTA Channel A Output of Error Amplifier. In measurement mode, normally connected directly to
VSTA.
16 VSTA The voltage applied to this pin sets the decibel value of the required RF input voltage to
Channel A that results in zero current flow in the loop integrating capacitor pin, CLPA.
18, 20 ACOM Analog Common for Channels A and B. Connect via low impedance to common.
21, 25, 32 VPSR, VPSA, VPSB Supply for the Input System of Channels A and B. Supply for the internal references. Connect
to +5 V power supply.
19 TEMP Temperature Sensor Output.
24 CHPA Connect to common via a capacitor to determine 3 dB point of Channel A input signal high-
pass filter.
26, 27 INHA, INLA Channel A High and Low RF Signal Input Terminal.
28 PWDN Disable/Enable Control Input. Apply logic high voltage to shut down the AD8364.
30, 31 INLB, INHB Channel B Low and High RF Signal Input Terminal.
Under
Package
Exposed Paddle The exposed paddle on the under side of the package should be soldered to a ground plane
Figure 13. Distribution of [OUTP − OUTN] Voltage and Error over
Temperature After Ambient Normalization vs. Input Amplitude for at Least
15 Devices from Multiple Lots, Frequency = 880 MHz, ADJ[A, B] =0.5 V, Sine
Wave, Differential Drive, P
4
2
0
–2
–4
–6
–8
–10
ERROR (dB)
–12
–14
SERIES NAME INDICATES THE POLARITY
–16
AND MAGNITUDE OF THE DEVIATION
APPLIED TO THE INHA INPUT, RELATIVE
–18
TO THE INLA INPUT, AS REFERENCED TO
THE REF SIGNAL.
–20
Ch. B = −25 dBm, Channel A Swept
IN
+30DEG
-15DEG
+1dB
+10DEG
+2dB
RF INPUT AT INLA (dBm)
+20DEG
REF
-2dB
-1dB
-10DEG
10–40 –35 –30 –25 –20 –15 –10 –505
05334-004
Figure 14. Log Conformance vs. Input Amplitude at Various Amplitude and
Figure 48. Output Voltage Stability vs. VP (Supply Voltage) at 2.14 GHz,
When VP Varies by 10%,ADJ[A, B] =0.85 V, Sine Wave, Differential Drive,
Murata LDB212G1020C-001
20–60–40–50–20–30010–10
05334-019
80
70
60
SUPPLY CURRENT (mA)
50
40
DECREASING
30
20
10
0
V
PWDN
Figure 49. Supply Current vs. V
V
INCREASING
V
PWDN
PWDN
(V)
PWDN
2.41.01.21.41.61.82.02.2
05334-020
Rev. 0 | Page 17 of 48
Page 18
AD8364
M
M
A
C
GENERAL DESCRIPTION AND THEORY
The AD8364 is a dual-channel, 2.7 GHz, true rms responding
detector with 60 dB measurement range. It incorporates two
AD8362 channels with shared reference circuitry (See the
AD8362 datasheet for more information). Multiple enhancements
have been made to the AD8362 cores to improve measurement
accuracy. Log-conformance peak-to-peak ripple has been reduced
to <±0.2 dB over the entire dynamic range. Temperature stability
of the rms output measurements provides <±0.5 dB error over
the specified temperature range of −40°C to 85°C through
proprietary techniques. The use of well-matched channels offers
extremely temperature-stable difference outputs, OUTP and
OUTN. Given well-matched channels through IC integration,
the rms measurement outputs, OUTA and OUTB, drift in the
same manner. With OUTP shorted to FBKA, the function at
OUTP is
OUTP = OUTA – OUTB + VLVL (1)
When OUTN is shorted to FBKB, the function at OUTN is
OUTN = OUTB – OUTA + VLVL (2)
OUTP and OUTN are insensitive to the common drift due to
the difference cancellation of OUTA and OUTB.
The AD8364 is a fully calibrated rms-to-dc converter capable of
operating on signals of a few hertz to 2.7 GHz or more. Unlike
logarithmic amplifiers, the AD8364 response is waveform
independent. The device accurately measures waveforms that
have a high peak-to-rms ratio (crest factor). Figure 50 shows a
block diagram.
A single channel of the AD8364 consists of a high performance
AGC loop. As shown in Figure 51, the AGC loop comprises
a wide bandwidth variable gain amplifier (VGA), square law
detectors, an amplitude target circuit, and an output driver. For
a more detailed description of the functional blocks, see the
AD8362 data sheet.
VPSA
INHA
INLA
PWDN
OMR
INLB
INHB
VPSB
INH[A, B]
INL[A, B]
CHP[A, B]
VST[A, B]
V
REF
25
26
27
28
29
30
31
32
CHPA
DECA
24232221201918 17
TEMP
CHANNEL A
TruPwr™
OUTA
OUTB
CHANNEL B
TruPwr™
BIAS
12345678
CHPB
DECB
COM
I
SIG
I
TGT
I
SIG
I
TGT
VGA
CONTROL
COMB
VPSR
VGA
CONTROL
2
2
2
2
ADJB
Figure 50. Block Diagram
V
IN
x
V
SIG
CLP [A, B]
C
LPF
EXTERNAL
2
OFFSET
NULLING
V
ST[A, B]
V
REF
2.5V
VGA
BAND GAP
REFERENCE
GSET
SETPOINT
INTERFACE
Figure 51. Single-Channel Details
ACO
ADJA
V
TEMP
VREF
2
x
REF
C
ACO
VLVL
TEMPERATURE
COMPENSATION
× 0.03
F
CLPA
CLPB
OUTPUT
BUFFER
16
15
14
13
12
11
10
9
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
ADJ[A, B]
OUT[A, B]
ACOM
05334-001
05334-023
Rev. 0 | Page 18 of 48
Page 19
AD8364
SQUARE LAW DETECTOR AND AMPLITUDE TARGET
The output of the VGA, called V
square law detector. The detector provides the true rms
response of the RF input signal, independent of waveform, up
to a crest factor of 6. The detector output, called I
fluctuating current with positive mean value. The difference
between I
integrated by C
and an internally generated current, I
SQU
and a capacitor attached to CLP[A, B]. CF is
F
the on-chip 25 pF filter capacitor. CLP[A, B] can be used to
arbitrarily increase the averaging time while trading off
response time. When the AGC loop is at equilibrium,
MEAN(I
SQU
) = I
(3)
TGT[A, B]
This equilibrium occurs only when
2
MEAN(V
where V
TGT
) = V
SIG
TGT[A, B]
is an attenuated version of the VREF voltage.
Because the square law detectors are electrically identical and
well matched, process and temperature dependant variations
are effectively cancelled.
By forcing the above identity through varying the VGA
setpoint, it is apparent that
RMS(V
) = √(MEAN(V
SIG
, is applied to a wideband
SIG
, is a
SQU
, is
TGT[A, B]
2
(4)
2
)) = √(V
SIG
TGT
2
) = V
(5)
TGT
RF INPUT INTERFACE
The AD8364’s RF inputs are connected as shown in Figure 52.
There are 100 Ω resistors connected between DEC[A, B] and
INH[A, B] and also between DEC[A, B] and INL[A, B]. The
DEC[A, B] pins have a dc level established as (7 × VPS[A, B] +
55 × V
2.5 V.
Signal-coupling capacitors must be connected from the input
signal to the INH[A, B] and INL[A, B] pins. The high-pass
corner is
A decoupling capacitor should be connected from DEC[A, B] to
ground to attenuate any signal at the midpoint. A 100 pF and
0.1 µF cap from DEC[A, B] to ground are recommended, with a
1 nF coupling capacitor such that signals greater than 1.6 MHz
can be measured. For coupling signals less than 1.6 MHz,
100 × C
)/30. With a 5 V supply, DEC[A, B] is approximately
BE
= 1/(2 × π × 100 × C) (8)
f
high-pas s
for the DEC[A, B] capacitor generally can be used.
coupling
DEC[A, B]
INH[A, B]
V
COM[A, B]
100Ω
IN
100Ω
VSP[A, B]
VGA
Substituting the value of V
RMS(G0 × RF
exp(−VST[A, B]/V
IN
, we have
SIG
GNS
)) = V
(6)
TGT
When connected as a measurement device VST[A, B] =
SLOPE
,
IN
may be
OUT[A, B]. Solving for OUT[A, B] as a function of RF
OUT[A, B] = V
where V
SLOPE
100 MHz. V
RMS(RF
) = VZ. If desired, the effective value of V
IN
is laser trimmed to 1 V/decade (or 50 mV/dB) at
is the intercept voltage, since Log 10(1) = 0 when
Z
× Log10(RMS(RFIN)/VZ) (7)
SLOPE
altered by using a resistor divider from OUT[A, B] to drive
VST[A, B]. The intercept, V
, is also laser trimmed to 180 µV
Z
(−62 dBm, referred to 50 Ω) with a CW signal at 100 MHz. This
value is extrapolated, because OUT[A, B] do not respond to input
of less than approximately −55 dBm with differential drive.
In most applications, the AGC loop is closed through the
setpoint interface, VST[A, B]. In measurement mode, OUT[A, B]
are tied to VST[A, B], respectively. In controller mode, a control
voltage is applied to VST[A, B]. Pins OUT[A, B] drive the control
input of a system. The RF feedback signal to the input pins is
forced to have an rms value determined by VSTA or VSTB.
INL[A, B]
VSP[A, B]
COM[A, B]
Figure 52. AD8364 RF Inputs
VSP[A, B]
COM[A, B]
05334-024
OFFSET COMPENSATION
An offset-nulling loop is used to address small dc offsets in the
VGA. The high-pass corner frequency of this loop is internally
preset to about 1 MHz using an on-chip capacitor of 25 pF
(1/(2 × 5K × 25 pF)), which is sufficiently low for most HF
applications. The high-pass corner can be reduced by a
capacitor from CHP[A, B] to ground. The input offset voltage
varies depending on the actual gain at which the VGA is
operating and, thus, on the input signal amplitude. When an
excessively large value of CHP[A, B] is used, the offset
correction process may lag the more rapid changes in the VGA’s
gain, which may increase the time required for the loop to fully
settle for a given steady input amplitude.
Rev. 0 | Page 19 of 48
Page 20
AD8364
L
L
TEMPERATURE SENSOR INTERFACE
The AD8364 provides a temperature sensor output capable of
driving about 1.6 mA. A 330 Ω-equivalent internal resistance is
connected from TEMP to COMR to provide current sink
capability. The temperature scaling factor of the output voltage is
approximately 2 mV/°C. The typical absolute voltage at 25°C is
about 620 mV.
VPSR
INTERNA
VPTAT
4kΩ
1kΩ
COMR
Figure 53. TEMP Interface Simplified Schematic
VREF INTERFACE
An internal voltage reference is provided to the user at Pin VREF.
The VREF voltage is a temperature stable 2.5 V reference that
can drive about 18 mA. An 830 Ω equivalent internal resistance
is connected from VREF to ACOM for 3 mA sink capability.
VPSR
INTERNA
VOLTAGE
9kΩ
1.465kΩ
350Ω
900Ω
TEMP
V
REF
05334-025
POWER-DOWN INTERFACE
The operating and stand-by currents for the AD8364 at 25°C are
approximately 70 mA and 500 µA, respectively. The PWDN pin
is connected to an internal resistor divider made with two 42 kΩ
resistors. The divider voltage is applied to the base of an NPN
transistor to force a power-down condition when the device is
active. Typically when PWDN is pulled greater than 2 V, the
device is powered down. Figure 46 and Figure 47 show typical
response times for various RF input levels. The output reaches
to within 0.1 dB of its steady-state value in about 1.6 µs; the
reference voltage is available to full accuracy in a much shorter
time. This wake-up response vary depending on the input
coupling means and the capacitances CDEC[A, B], CHP[A, B],
and CLP[A, B].
PWDN
42kΩ
42kΩ
COMR
Figure 55. PWDN Interface Simplified Schematic
POWER DOWN
SIGNAL
05334-027
VST[A, B] INTERFACE
The VST[A, B] interface has a high input impedance of 72 kΩ.
The voltage at VST[A, B] is converted to an internal current
used to steer the VGA gain. The VGA attenuation control is
set to 20 dB/V.
The output drivers used in the AD8364 are different than the
output stage on the AD8362. The AD8364 incorporates rail-torail output drivers with pull-up and pull-down capabilities.
The output noise is approximately 40 nV/√Hz at 100 kHz.
OUT[A, B, P, N] can source and sink up to 70 mA. There is also an
internal load from both OUTA and OUTB to ACOM of 2.5 kΩ.
MEASUREMENT CHANNEL DIFFERENCE OUTPUT
USING OUT[P, N]
The AD8364 incorporates two operational amplifiers with railto-rail output capability to provide a channel difference output.
As in the case of the output drivers for OUT[A, B], the output
stages have the capability of driving 70 mA. The output noise is
approximately 40 nV/√Hz at 100 kHz. OUTA and OUTB are
internally connected through 1 kΩ resistors to the inputs of each
op amp. The pin VLVL is connected to the positive terminal of
both op amps through 1 kΩ resistors to provide level shifting. The
negative feedback terminal is also made available through a 1 kΩ
resistor. The input impedance of VLVL is 1 kΩ and FBK[A, B]
is 2 kΩ. See Figure 59 for the connections of these pins.
CONTROLLER MODE
The channel difference outputs can be used for controlling a
feedback loop to the AD8364’s RF inputs. A capacitor connected
between FBKA and OUTP forms an integrator, keeping in mind
that the on-chip 1 kΩ feedback resistor forms a zero. (The value
of the on-chip resistors can vary as much as ±20% with manufacturing process variation.) If Channel A is driven and Channel B
has a feedback loop from OUTP through a PA, then OUTP
integrates to a voltage value such that
OUTB = (OUTA + VLVL)/2 (11)
The output value from OUTN may or may not be useful. It is
given by
VPSA
INHA
INLA
PWDN
OMR
INLB
INHB
VPSB
CHPA
DECA
24232221201918 17
TEMP
25
26
27
28
29
30
31
32
CHANNEL A
TruPwr™
OUTA
OUTB
CHANNEL B
TruPwr™
BIAS
12345678
CHPB
DECB
COM
I
SIG
I
TGT
I
SIG
I
TGT
VGA
CONTROL
COMB
VPSR
VGA
CONTROL
2
2
ADJB
TEMP
ACO
2
2
VREF
ADJA
ACO
VLVL
CLPA
16
VSTA
15
OUTA
14
FBKA
13
OUTP
12
OUTN
11
FBKB
10
OUTB
9
VSTB
CLPB
05334-001
Figure 59. Op Amp Connections (All Resistors are 1 kΩ ± 20%)
If OUTP is connected to FBKA, then OUTP is given as
OUTP = OUTA – OUTB + VLVL (9)
If OUTN is connected to FBKB, then OUTN is given as
OUTN = 0 V (12)
For VLVL < OUTA/3,
Otherwise,
OUTN = (3 × VLVL – OUTA)/2 (13)
If VLVL is connected to OUTA, then OUTB is forced to equal
OUTA through the feedback loop. This flexibility provides the
user with the capability to measure one channel operating at a
given power level and frequency while forcing the other channel
to a desired power level at another frequency. ADJA and ADJB
should be set to different voltage levels to reduce the temperature
drift of the output measurement. The temperature drift will be
statistical sum of the drift from Channel A and Channel B. As
stated before, VLVL can be used to force the slaved channel to
operate at a different power than the other channel. If the two
channels are forced to operate at different power levels, then
some static offset occurs due to voltage drops across metal
wiring in the IC.
If an inversion is necessary in the feedback loop, OUTN can be
used as the integrator by placing a capacitor between OUTN
and OUTP. This changes the output equation for OUTB and
OUTP to
OUTN = OUTB – OUTA + VLVL (10)
In this configuration, all four measurements, OUT[A, B, P, N],
OUTB = 2 × OUTA − VLVL (14)
For VLVL < OUTA/2,
are made available simultaneously. A differential output can be
taken from OUTP − OUTN, and VLVL can be used to adjust
the common-mode level for an ADC connection.
OUTN = 0 V (15)
Otherwise,
OUTN = 2 × VLVL – OUTA (16)
The previous equations are valid when Channel A is driven and
Channel B is slaved through a feedback loop. When Channel B
is driven and Channel A is slaved, the above equations can be
altered by changing OUTB to OUTA and OUTN to OUTP.
Rev. 0 | Page 22 of 48
Page 23
AD8364
RF MEASUREMENT MODE BASIC CONNECTIONS
The AD8364 requires a single supply of nominally 5 V. The
supply is connected to the three supply pins, VPSA, VPSB, and
VPSR. Each pin should be decoupled using the two capacitors
with values equal or similar to those shown in Figure 60. These
capacitors must provide a low impedance over the full
frequency range of the input, and they should be placed as close
as possible to the VPOS pins. Two different capacitors are used
in parallel to provide a broadband ac short to ground.
The input signals are applied to the input differentially. The RF
inputs of the AD8364 have a differential input impedance of
200 Ω. When the AD8364 RF inputs are driven from a 50 Ω
source, a 4:1 balun transformer is recommended to provide the
necessary impedance transformation. The inputs can be driven
single-ended, however, this reduces the measurement range of
the rms detectors (see the Single-Ended Input Operation
section).
The device is placed in measurement mode by connecting OUTA
and/or OUTB to VSTA and/or VSTB, respectively. This closes the
AGC loop within the device with OUT[A, B] representing the
VGA control voltage, which is required to present the correct
rms voltage at the input of the internal square law detector.
As the input signal to Channel A and Channel B are swept over
their nominal input dynamic range of +10 dBm to −50 dBm,
the output swings from 0 V to 3.5 V. The voltages OUTA and
OUTB are also internally applied to a difference amplifier with
a gain of two. So as the dB difference between INA and INB
ranges from approximately −30 dB to +30 dB, the difference
voltage on OUTP and OUTN swings from −3.5 V to +3.5 V.
Input differences larger than ±30 dB can be measured as long as
the absolute input level at INA and INB are within their nominal
ranges of +10 dBm to −50 dBm. However, measurement of large
differences between INA and INB are affected by on-chip signal
leakage (see the Channel Isolation section). The common-mode
level of OUTP and OUTN is set by the voltage applied to VLVL.
These output can be easily biased up to a common-mode
voltage of 2.5 V by connecting VREF to VLVL. As the gain range
is swept, OUTP swings from approximately 1 V to 4.5 V and
OUTN swings from 4.5 V to 1 V.
Rev. 0 | Page 23 of 48
Page 24
AD8364
C23
100pF
VPOS
C11
INPA
INPB
C5
0.1µF
1:4
1:4
C2
0.1µF
0.1µF
C10
100pF
T2
T1
C7
0.1µF
C6
0.1µF
C4
0.1µF
C3
0.1µF
VPOS
C9
0.1µFC90.1µF
CHPACLPAACOMTEMPACOMVPSRCOMADECA
2516
VPSA
26
INHA
27
INLA
28
PWDN
29
COMR
30
INLB
31
INHB
32
VPSB
C20
100pF
C21
0.1µF
CHPBCLPBVLVLVREFADJAADJBCOMBDECB
C22
0.1µF
C1
0.1µF
VPOS
R24
0Ω
R5
0Ω
C8
0.1µF
AD8364ACPZ
EXPOSED PADDLE
C24
100pF
R19
C13
0.1µF
C12
100pF
C19
0.1µF
1
R18
R17
1
1
R20
1
C14
0.1µF
1819172021222423
VSTA
15
OUTA
14
FBKA
13
OUTP
12
OUTN
11
FBKB
10
OUTB
9
VSTB
76854312
C16
0.1µF
OUTA
OUTP
OUTN
OUTB
Figure 60. Basic Connections for Operation in Measurement Mode
CONTROLLER MODE BASIC CONNECTIONS
In addition to being a measurement device, the AD8364 can
also be configured to measure and control rms signal levels. The
AD8364 has two controller modes. Each of the two rms log
detectors can be separately configured to set and control the
output power level of a variable gain amplifier (VGA) or
variable voltage attenuator (VVA). Alternatively, the two rms
log detectors can be configured to measure and control the gain
of an amplifier or signal chain.
Automatic Power Control
Figure 61 shows how the device should be reconfigured to
control output power.
The RF input to the device is configured as before. A directional
coupler taps off some of the power being generated by the VGA
(typically a 10 dB to 20 dB coupler is used). A power splitter can
be used instead of a directional coupler if there are no concerns
about reflected energy from the next stage in the signal chain.
Some additional attenuation may be required to set the
maximum input signal at the AD8364 to be equal to the
1
SEE TEXT.
05334-031
recommended maximum input level for optimum linearity and
temperature stability at the frequency of operation.
VSTA and OUTA are no longer shorted together. OUTA now
provides a bias or gain control voltage to the VGA. The gain
control sense of the VGA must be negative and monotonic, that
is, increasing voltage tends to decrease gain. However, the gain
control transfer function of the device does not need to be well
controlled or particularly linear. If the gain control sense of the
VGA is positive, an inverting op amp circuit with a dc offset
shift can be used between the AD8364 and the VGA to keep the
gain control voltage in the 0 V to 5 V range.
VSTA becomes the setpoint input to the system. This can be
driven by a DAC, as shown in Figure 61, if the output power is
expected to vary, or it can simply be driven by a stable reference
voltage if constant output power is required. This DAC should
have an output swing that covers the 0 V to 3.5 V range. The
AD7391 and AD7393 serial-input and parallel-input 10-bit
DACs provide adequate resolution (4 mV/bit) and an output
swing up to 4.5 V.
Rev. 0 | Page 24 of 48
Page 25
AD8364
When VSTA is set to a particular value, the AD8364 compares
this value to the equivalent input power present at the RF input.
If these two values do not match, OUTA increases or decreases
in an effort to balance the system. The dominant pole of the
error amplifier/integrator circuit that drives OUTA is set by the
capacitance on Pin CLPA; some experimentation may be
necessary to choose the right value for this capacitor. In general,
CLPA should be chosen to provide stable loop operation for the
complete output power control range. If the slope (in dB/V) of
the gain control transfer function of the VGA is not constant,
CLPA must be chosen to guarantee a stable loop when the gain
control slope is at its maximum. On the other hand, CLPA must
provide adequate averaging to the internal low range squaring
detector so that the rms computation is valid. Larger values of
CLPA tend to make the loop less responsive.
The relationship between VSTA and the RF input follows from
the measurement mode behavior of the device. For example,
from Figure 9, which shows the measurement mode transfer
function at 880 MHz, it can be seen that an input power of
−10 dBm yields an output voltage of 2.5 V. Therefore, in
controller mode, VSTA should be set to 2.5 V, which results in
an input power of −10 dBm to the AD8364.
Automatic Gain Control
Figure 62 shows how the AD8364 can be connected to provide
automatic gain control to an amplifier or signal chain.
Additional pins are omitted for clarity. In this configuration,
both rms detectors are connected in measurement mode with
appropriate filtering being used on CLP[A, B] to effect a valid
rms computation on both channels. OUTA, however, is also
connected to the VLVL pin of the on-board difference amplifier.
Also, the OUTP output of the difference amplifier drives a
variable gain element (either VVA or VGA) and is connected
back to the FBKA input via a capacitor so that it is operating as
an integrator.
Assume that OUTA is much bigger than OUTB. Because OUTA
also drives VLVL, this voltage is also present on the noninverting
input of the op amp driving OUTP. This results in a net current
flow from OUTP through the integrating capacitor into the
FBKA input. This results in the voltage on OUTP increasing. If
the gain control transfer function of the VVA/VGA is positive,
this increases the gain, which in turn increases the input signal
to INHB. The output voltage on the integrator continues to
increase until the power on the two input channels is equal,
resulting in a signal chain gain of unity.
VGA OR VVA
P
(OUTPUT POWER
IN
DECREASES AS
V
INCREASES)
APC
V
APC
(0V TO 4.9V AVAILABLE SWING)
1:4
C5
0.1µF
OUTA
INHA
AD8364
INLA
INHA
VSTA
DAC
0V TO 3.5V
Figure 61. Operation in Controller Mode for Automatic Power Control
C7
0.1µF
C6
0.1µF
SEE TEXT
T2
ATTENUATOR
If a gain other than 0 dB is required, an attenuator can be used
in one of the RF paths, as shown in Figure 62. Alternatively,
P
OUT
power splitters or directional couplers of different coupling
factors can be used. Another convenient option is to apply a
voltage on VLVL other than OUTA. Refer to Equation 11 and
the Controller Mode section for more detail.
If the VGA/VVA has a negative gain control sense, the OUTN
output of the difference amplifier can be used with the
integrating capacitor tied back to FBKB.
The choice of the integrating capacitor affects the response time
of the AGC loop. Small values give a faster response time but
can result in instability, whereas larger values reduce the response
time. Note that in this mode, the capacitors on CLPA and CLPB,
05334-032
which perform the rms averaging function, must still be used
and also affect the loop response time.
Rev. 0 | Page 25 of 48
Page 26
AD8364
DIRECTIONAL
OR
POWER SPLITTER
C5
0.1µF
1:4
1:4
C2
0.1µF
T2
1:4
T1
1:4
C7
0.1µF
C6
0.1µF
C4
0.1µF
C3
0.1µF
INHA
INLA
INLB
INHB
CHANNEL A
TruPwr™
AD8364
CHANNEL B
TruPwr™
OUTA
OUTB
CONTROL
I
SIG
I
TGT
2
I
SIG
2
I
TGT
CONTROL
2
2
VGA
VGA
VLVL
I
ERR
CLPF
CLPF
VGA/VVA
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
C
INT
DIFF OUT +
DIRECTIONAL
OR
POWER SPLITTER
ATTENUATOR
05334-054
Figure 62. Operation in Controller Mode for Automatic Gain Control
Rev. 0 | Page 26 of 48
Page 27
AD8364
CONSTANT OUTPUT POWER OPERATION
In controller mode, the AD8364 can be used to hold the output
power stable over a broad temperature/input power range. This
can be very useful in systems, such as a transmit module driving
a high power amplifier (HPA) in a basestation, that connect
multiple power sensitive modules together. In applications
where stable output power is needed, the RF output is
connected to Channel B using a coupler, VLVL is connected to
VREF, VSTB is used to set the power to a particular level and
can be controlled using a DAC or a dc voltage, OUTB is used to
drive the gain control of an amplifier that is capable of negativegain law conformance (such as the AD8367), and ADJB (set at
0 V in this example) is used to control the temperature drift.
Using this configuration, the RF input signal is down converted
to 80 MHz using the AD8343 and amplified using the AD8367.
The signal then splits and part of it is fed back to the AD8364
through Channel B, and a setpoint voltage is applied to VSTB.
This voltage corresponds to a particular power level, which is
determined by the slope of the AD8364. The power detected at
the input of the AD8364 is compared with this voltage, and the
voltage present at OUTB is adjusted up or down to match the
setpoint voltage, with the power detected on the input. The
OUTB voltage is connected to the gain control of the AD8367
VGA and increases or decreases the gain of the AD8367,
resulting in the output power being held constant, regardless of
variations in the input power. The AD8364 is able to maintain a
fixed output power from the AD8367 even though its input
power is changing. The input power can vary over a 36 dB
range, while the output power remains constant and the drift
over temperature is less than 0.2 dB
Figure 64 shows a constant output power circuit using the
AD8364 and the AD8367 VGA. The input power was swept
from +3 dBm to −35 dBm, the output power was measured at
multiple temperatures between −40°C and +85°C, and the
power changed less than ±0.07 dB (Figure 63).
–15.0
–15.1
–15.2
–15.3
–15.4
–15.5
(dBm)
–15.6
OUT
P
–15.7
–15.8
–15.9
–16.0
Figure 63. AD8364 Constant Power Performance
P
+25°C
OUT
–20°C
P
–40°C
OUT
PIN (dBm)
P
+85°C
OUT
5–40–35 –30–20–15–25–10–50
05334-033
Rev. 0 | Page 27 of 48
Page 28
AD8364
RFIN
1880MHz
INPA
J3
PWDN
J2
INPBJ11:4
R23
T2
LDB181G8820C-110
C5
0.1µF
1:4
A
SW1
VPOS
C5
0.1µF
B
T1
ETK4-2T
10kΩ
0Ω
R4
0Ω
R2
C4
0.1µF
0.1µF
R21
0Ω
COMM
0.1µF
OPEN
0.1µF
OPEN
C3
VPOS
TP1
TP2
AD8343
VPOS
R24
0Ω
C23
100pF
C11
0.1µF
C9
0.1µFC90.1µF
C10
100pF
CHPACLPAACOMTEMPACOMVPSRCOMADECA
2516
VPSA
C8
0.1µF
C7
26
C20
100pF
C21
0.1µF
27
28
29
30
31
32
INHA
INLA
PWDN
COMR
INLB
INHB
VPSB
0.1µF
C1
CHPBCLPBVLVLVREFADJAADJBCOMBDECB
C22
0.1µF
C24
100pF
AD8364ACPZ
R20
R3
C6
R1
C13
R5
0.1µF
0Ω
C12
100pF
EXPOSED PADDLE
0Ω
R18
0Ω
0.705V
C19
0.1µF
R16
OPEN
C14
0.1µF
TEMP
SENSOR
J4
1819172021222423
76854312
C18
OPEN
90MHz
LPF
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
C15
0.1µF
C17
0.1µF
IFOUT
80MHz
107Ω
11dB
COUPLING
MODE SEL
0V TO 1.2V
R12
0Ω
VSTB
0.4V TO
3.4V
0Ω 0Ω
AD8367
R6
0Ω
R9
0Ω
15
R10
0Ω
14
13
12
R11
0Ω
11
10
9
R13
R14
OPEN
OPEN
R15
0Ω
C16
0.1µF
VREF
05334-055
Figure 64. Constant Output Power Circuit
Rev. 0 | Page 28 of 48
Page 29
AD8364
GAIN-STABLE TRANSMITTER/RECEIVER
There are many applications for a transmitter or receiver with a
highly accurate temperature-stable gain. For example, a
multicarrier basestation high power amplifier (HPA) using
digital predistortion has a power detector and an auxiliary
receiver. The power detector and all parts associated with it can
be removed if the auxiliary receiver has a highly accurate
temperature-stable gain. With a set gain receiver, the ADC on
the auxiliary receiver can not only determine the overall power
being transmitted but can also determine the power in each
carrier for a multicarrier HPA.
In controller mode, the AD8364 can be used to hold the
receiver gain constant over a broad input power/temperature
range. In this application, the difference outputs are used to
hold the receiver gain constant.
The RF input is connected to INPA, using a 19.1 dB coupler,
and the down converted output from our signal chain is
connected to INPB, using a 10.78 dB coupler. A 0.1 µF capacitor
is connected between FBKA and OUTP, forming an integrator.
OUTA is connected to VLVL, forcing OUTP to adjust the VGA
so that OUTB is equal to OUTA. The circuit gain is set by the
difference in the coupling values of the input and output
couplers. As noted, OUTP is used to drive the gain control of
the ADL5330 by adjusting the gain up or down as needed to
force the power at the AD8364 inputs to be equal in amplitude.
Since operating at different frequencies, the appropriate voltages
on the ADJ[A, B] pins must be supplied. Because INPA is
operating at 1880 MHz, ADJA is set to 0.75 V. Likewise, because
INPB is operating at 80 MHz, ADJB is set to 0 V.
Because the difference in the coupler values is 8.32 dB, a fixed
gain of −8.32 dB is expected. In practice, there is a gain of
−13 dB. This is caused by the intercept shift of the AD8364 due
to its frequency response, the insertion loss of the output
coupler, and the insertion loss differences of the baluns used on
the input of the AD8364. In this configuration, approximately
33 dB of control range with 0.5 dB drift over temperature is
obtained.
Figure 66 shows a gain-stable receiver amplifier circuit using
the AD8364 to control an ADL5330 VGA and the AD8343
mixer. The input power was swept from +3 dBm to −35 dBm,
the output power was measured, and the gain was calculated at
multiple temperatures between −40°C and +85°C. Note that the
gain changed less than ±0.45 dB over this range (Figure 65).
Most of the gain change was caused by performance differences
at different frequencies.
–11.0
–11.5
GAIN (dB)
–12.0
–12.5
–13.0
–13.5
–14.0
Figure 65. Performance of Gain-Stable Receiver
PIN (dBm)
–40°C
+25°C
+85°C
5–40–25–15–5–20–35–30–100
05334-034
Rev. 0 | Page 29 of 48
Page 30
AD8364
RFIN
1880MHz
INPA
J3
PWDN
J2
INPBJ11:4
0Ω 0Ω
454Ω
19dB
COUPLING
R23
T2
LDB181G8820C-110
C5
0.1µF
1:4
A
SW1
VPOS
C5
0.1µF
B
T1
ETK4-2T
10kΩ
0Ω
R4
0Ω
R2
C4
0.1µF
0.1µF
R21
0Ω
COMM
0.1µF
OPEN
0.1µF
OPEN
C3
VPOS
TP1
TP2
ADL5330
AD8343
MODE SEL
0V TO 1.2V
VPOS
R24
0Ω
C23
100pF
C11
0.1µF
C9
0.1µFC90.1µF
C10
100pF
CHPACLPAACOMTEMPACOMVPSRCOMADECA
2516
VPSA
C8
0.1µF
C7
26
C20
100pF
C21
0.1µF
27
28
29
30
31
32
INHA
INLA
PWDN
COMR
INLB
INHB
VPSB
0.1µF
C1
CHPBCLPBVLVLVREFADJAADJBCOMBDECB
C22
0.1µF
C24
100pF
R20
R3
C6
R1
R5
0Ω
AD8364
0Ω
C13
0.1µF
C12
100pF
0.75V
R18
0Ω
VREF
C19
0.1µF
R16
OPEN
C14
0.1µF
TEMP
SENSOR
J4
1819172021222423
76854312
C18
OPEN
90MHz
LPF
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
C15
0.1µF
C17
0.1µF
0Ω 0Ω
IFOUT
80MHz
107Ω
11dB
COUPLING
R6
0Ω
R9
0Ω
15
0.1µF
14
R11
0Ω
R15
0Ω
R13
OPEN
DIFF OUT +
R12
0Ω
R14
OPEN
C16
0.1µF
13
12
11
10
9
05334-056
Figure 66. Gain-Stable Receiver Circuit
Rev. 0 | Page 30 of 48
Page 31
AD8364
A
TEMPERATURE COMPENSATION ADJUSTMENT
The AD8364 has a highly stable measurement output with
respect to temperature. However, when the RF inputs exceed a
frequency of 600 MHz, the output temperature drift must be
compensated for using ADJ[A, B] for optimal performance.
Proprietary techniques are used to compensate for the temperature drift. The absolute value of compensation varies with
frequency, balun choice, and circuit board material. Table 5
shows recommended voltages for ADJ[A, B] to maintain a
temperature drift error of typically ±0.5 dB or better over the
entire rated temperature range with the recommended baluns.
Table 5. Recommended Voltages for ADJ[A, B]
Frequency (MHz)
ADJ[A, B] (V)
Compensating the device for temperature drift using ADJ[A, B]
allows for great flexibility. If the user requires minimum temperature drift at a given input power or subset of the dynamic range,
the ADJ[A, B] voltage can be swept while monitoring OUT[A, B]
over temperature. Figure 67 shows the result of such an exercise
with a broadband balun, one that is not the recommended balun
at 1880 MHz. The value of ADJ[A, B] where the output has
minimum movement (approximately 0.77 V for the example in
Figure 67) is the recommended voltage for ADJ[A, B] to achieve
minimum temperature drift at a given power and frequency.
1.70
1.65
1.60
1.55
OUTA (V)
1.50
1.45
1.40
Figure 67. OUTA vs. ADJA over Temp. Pin = −30 dBm, 1.9 GHz
450 880 1880 2140 2500
0 0.5 0.65 0.85 1.10
+85°C
+65°C
+45°C
+25°C
+10°C
–20°C
–40°C
ADJA (V)
2.5000.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25
05334-035
Figure 68 shows a simplified schematic representation of the
ADJ[A, B] interface.
The measured transfer function of the AD8364 at 2.14 GHz is
shown in Figure 69. The figure shows plots of both output
voltage vs. input power and calculated error vs. input power. As
the input power varies from −50 dBm to 0 dBm, the output
voltage varies from 0.4 V to about 2.8 V.
3.50
3.15
2.80
2.45
(V)
2.10
OUT
V
1.75
2
V
OUT
1.40
1.05
0.70
1
V
OUT
0.35
0
INTERCEPT
ERROR CW –40°C
ERROR CW +25°C
PIN1
BLUE = –40°C
GREEN = +25°C
RED = +85°C
2
P
IN
ERROR CW +85°C
P
MEAS (dBm)
IN
Figure 69. Transfer Function at 2.14 GHz.
Because slope and intercept vary from device to device, boardlevel calibration must be performed to achieve high accuracy.
The equation for output voltage can be written as
= Slope × (PIN − Intercept)
V
OUT
2.0
1.6
1.2
0.8
0.4
0
–0.4
–0.8
–1.2
–1.6
–2.0
10–60–45 –40 –35–55 –50–25 –20 –15–30–5 0 5–10
ERROR (dB)
04862-037
The ADJ[A, B] input has high input impedance. The input can
be conveniently driven from an attenuated value of VREF using
a resistor divider, if desired.
Where Slope is the change in output voltage divided by the
change in power (dB), and Intercept is the calculated power at
which the output voltage would be 0 V. (Note that Intercept is a
theoretical value; the output voltage can never achieve 0 V).
In general, the calibration is performed by applying two known
signal levels to the AD8364’s input and measuring the
corresponding output voltages. The calibration points are
generally chosen to be within the linear-in-dB operating range
Rev. 0 | Page 31 of 48
of the device (see the Specifications section for more details).
Page 32
AD8364
Calculation of the slope and intercept is done using the
equations:
Slope = (V
Intercept = P
OUT1
− V
IN1
Once slope and intercept have been calculated, an equation can
be written that will allow calculation of the input power based
on the output voltage of the detector.
(unknown) = (V
P
IN
The log conformance error of the calculated power is given by
Error (dB) = (V
)/(P
OUT2
− (V
OUT1
OUT1(measured)
OUT(MEASURED)
− P
IN1
IN2
/Slope)
/Slope) + Intercept
− V
OUT(IDEAL)
)
)/Slope
Calibration points should be chosen to suit the application at
hand. In general, though, do not choose calibration points in
the nonlinear portion of the log amp’s transfer function (above
0 dBm or below −50 dBm in this case).
Figure 71 shows how calibration points can be adjusted to
increase dynamic range, but at the expense of linearity. In this
case, the calibration points for slope and intercept are set at
−1 dBm and −50 dBm. These points are at the end of the
device’s linear range. At 25°C, there is an error of 0 dB at the
calibration points. Note also that the range over which the
AD8364 maintains an error of <±0.4 dB is extended to 57 dB at
25°C. The disadvantage of this approach is that linearity suffers,
especially at the top end of the input range.
Figure 69 includes a plot of the error at 25°C, the temperature at
which the log amp is calibrated. Note that the error is not zero.
This is because the log amp does not perfectly follow the ideal
vs. PIN equation, even within its operating region. The
V
OUT
error at the calibration points (−43 dBm and −23 dBm in this
case) will, however, be equal to zero by definition.
Figure 69 also includes error plots for the output voltage at
−40°C and +85 °C. These error plots are calculated using the
slope and intercept at 25°C. This is consistent with calibration
in a mass-production environment, where calibration at
temperature is not practical.
SELECTING CALIBRATION POINTS TO IMPROVE
ACCURACY OVER A REDUCED RANGE
In some applications, very high accuracy is required at one
power level or over a reduced input range. For example, in a
wireless transmitter, the accuracy of the high power amplifier
(HPA) is most critical at or close to full power.
Figure 70 shows the same measured data as Figure 69. Notice
that accuracy is very high from −10 dBm to −25 dBm. At
approximately −45 dBm, the error increases to about −0.3 dB
because the calibration points have been changed to −15 dBm
and −25 dBm.
Another way of presenting the error function of a log amp
detector is shown in Figure 72. In this case, the dB error at hot
and cold temperatures is calculated with respect to the output voltage at ambient. This is a key difference in comparison to the
previous plots, in which all errors have been calculated with
respect to the ideal transfer function at ambient.
When the alternative technique, the error at ambient becomes
by definition equal to 0 (see Figure 72).
This would be valid if the device transfer function perfectly
followed the ideal V
= Slope × (PIN − Intercept) equation.
OUT
However, since an rms amp, in practice, never perfectly follows
this equation (especially outside of its linear operating range),
this plot tends to artificially improve linearity and extend the
dynamic range, unless enough calibration points were taken to
remove the error. This plot is a useful tool for estimating temperature drift at a particular power level with respect to the (nonideal)
output voltage at ambient.
Rev. 0 | Page 32 of 48
Page 33
AD8364
V
3.50
3.15
2.80
(V)
2.45
OUT
V
2.10
V
2
OUT
1.75
1
V
OUT
1.40
1.05
0.70
0.35
INTERCEPT
ERROR CW –40°C
ERROR CW +25°C
ERROR CW +85°C
0
PIN MEAS (dBm)
Figure 70. Output Voltage and Error vs. P
BLUE = –40°C
GREEN = +25°C
RED = +85°C
PIN1
2
P
IN
with 2-Point Calibration at
IN
2.0
1.6
1.2
0.8
0.4
0
–0.4
–0.8
–1.2
–1.6
–2.0
10–60–45 –40 –35–55 –50–25 –20 –15–30–5 0 5–10
−15 dBm and −25 dBm, 2.14 GHz
OUT
(V)
OUT
V
PIN1P
3.50
3.15
ERROR CW –40°C
2.80
2.45
2.10
ERROR CW +25°C
1.75
1.40
ERROR CW +85°C
1.05
0.70
1
0.35
0
MEAS (dBm)
P
IN
57dB DYNAMIC RANGE
2
IN
2.0
1.6
V
1.2
OUT
0.8
0.4
0
–0.4
ERROR (dB)
–0.8
–1.2
–1.6
–2.0
10–60–45 –40 –35–55 –50–25 –20 –15–30–5 0 5–10
Figure 71. Dynamic Range Extension by Choosing Calibration Points that are
Close to the End of the Linear Range, 2.14 GHz
ERROR (dB)
04862-038
2
04862-039
3.50
3.15
ERROR CW –40°C
2.80
2.45
ERROR CW +25°C
ERROR CW +85°C
(V)
V
OUT
2.10
1.75
1.40
1.05
0.70
0.35
0
P
MEAS (dBm)
IN
2.0
1.6
1.2
0.8
0.4
0
–0.4
ERROR (dB)
–0.8
–1.2
–1.6
–2.0
10–60–45 –40 –35–55 –50–25 –20 –15–30–5 0 5–10
04862-040
Figure 72. Error vs. Temperature with Respect to Output Voltage at 25 °C,
2.14 GHz (Does Not Account for Transfer Function Nonlinearities at 25°C)
Rev. 0 | Page 33 of 48
Page 34
AD8364
M
M
A
ALTERING THE SLOPE
None of the changes to operating conditions discussed so far
affect the logarithmic slope, V
readily be altered by controlling the fraction of OUT[A, B] that
is fed back to the setpoint interface at the VST[A, B] pin. When
the full signal from OUT[A, B] is applied to VST[A, B], the
slope assumes its nominal value of 50 mV/dB. It can be
increased by including a voltage divider between these pins, as
shown in Figure 73. Moderately low resistance values should be
used to minimize scaling errors due to the approximately 70 kΩ
input resistance at the VST[A, B] pin. Keep in mind that this
resistor string also loads the output, and it eventually reduces
the load-driving capabilities if very low values are used.
Equation 17 can be used to calculate the resistor values.
R1 = R2' (S
/50 − 1) (17)
D
where:
is the desired slope, expressed in mV/dB.
S
D
R2' is the value of R2 in parallel with 70 kΩ.
For example, using R1 = 1.65 kΩ and R2 = 1.69 kΩ (R2' =
1.649 kΩ), the nominal slope is increased to 100 mV/dB. This
choice of scaling is useful when the output is applied to a digital
voltmeter because the displayed number directly reads as a
decibel quantity with only a decimal point shift.
Operating at a high slope is useful when it is desired to measure
a particular section of the input range in greater detail. A
measurement range of 60 dB would correspond to a 6 V change
in VOUT at this slope, exceeding the capacity of the AD8364’s
output stage when operating on a 5 V supply. This requires that
the intercept is repositioned to place the desired input range
section within a window corresponding to an output range of
0.1 V ≤ VOUT ≤ 4.8 V, a 47 dB range.
Using the arrangement shown in Figure 74, an output of 0.4 V
corresponds to the lower end of the desired range, and an
output of 3.5 V corresponds to the upper limit with 3 dB of
margin at each end of the range, nominally −32 dBm to −1 dBm
with the intercept at −35.6 dBm. Note that R2 is connected to
VREF rather than ground. R3 is needed to ensure that the
AD8364’s reference buffer is correctly loaded.
When the slope is raised by some factor, the loop capacitor,
CLP[A, B], should be raised by the same factor to ensure
stability and to preserve a chosen averaging time. The slope can
be lowered by placing a voltage divider after the output pin,
following standard practice.
, in Equation 7. The slope can
SLOPE
VPSA
INHA
INLA
PWDN
COMR
INLB
INHB
VPSB
CHPA
2423 2221 2019 18 17
TEMP
25
26
CHANNEL A
27
28
29
30
31
32
TruPwr™
CHANNEL B
TruPwr™
12345678
CHPB
DECA
OUTA
OUTB
BIAS
DECB
COM
I
SIG
I
TGT
I
SIG
I
TGT
VGA
CONTROL
COMB
ACO
VPSR
VGA
CONTROL
2
2
2
2
ADJA
ADJB
TEMP
VREF
ACO
VLVL
CLPA
CLPB
16
VSTA
15
OUTA
14
FBKA
13
OUTP
12
OUTN
11
FBKB
10
OUTB
9
VSTB
V
R1
R2
Figure 73. External Network to Raise Slope
VPSA
INHA
INLA
PWDN
COMR
INLB
INHB
VPSB
CHPA
2423 222120 1918 17
TEMP
25
26
27
28
29
30
31
32
CHANNEL A
TruPwr™
CHANNEL B
TruPwr™
12345678
CHPB
DECA
OUTA
OUTB
BIAS
DECB
COMA
I
SIG
I
TGT
I
SIG
I
TGT
VGA
CONTROL
COMB
VGA
CONTROL
VPSR
2
2
2
2
ADJB
ACOM
ADJA
TEMP
Figure 74. Scheme Providing 100 mV/dB Slope for Operation over a 3 mV to
300 mV Input Range
VREF
ACOM
VLVL
CLPA
CLPB
16
VSTA
15
OUTA
14
FBKA
13
OUTP
12
OUTN
11
FBKB
V
OUTB
10
9
VSTB
R1
4.02kΩ
R2
4.32kΩ
R3
2kΩ
OUT
OUT
05334-041
05334-042
Rev. 0 | Page 34 of 48
Page 35
AD8364
CHANNEL ISOLATION
Isolation must be considered when using both channels of the
AD8364 at the same time. The two isolation requirements that
should be considered are the isolation from one RF channel
input to the other RF channel input and the isolation from one
RF channel input to the other channel output. When using both
channels of the AD8364, care should be taken in the layout to
isolate the RF inputs from each other. Coupling on the PC
board affects both types of isolation.
In most applications, the designer has the ability to adjust the
power going into the AD8364 through the use of different
valued temperature-stable couplers and accurate temperaturestable attenuators. When isolation is a concern, it is useful to
adjust the input power so the lowest expected detectable power
is not far from the lowest detectable power of the AD8364 at the
frequency of operation. The AD8364’s lowest detectable power
point has little variation from part to part and is not affected by
the balun. This equalizes the signals on both channels at their
lowest possible power level, which reduces the overall isolation
requirements and possibly adds attenuators to the RF inputs of
the device, reducing the RF channel input isolation requirements.
Measuring the RF channel input to the other RF channel input
isolation is straight forward, and the result of such an exercise is
shown in Figure 75. Note that adding an attenuator in series
with the RF signal increases the channel input-to-input
isolation by the value of the attenuator.
The isolation between one RF channel input and the other
channel output is a little more complicated. Do not assume that
worst-case isolation happens when one RF channel has high
power and the other RF channel is set at its lowest detectable
power. Worst-case isolation happens when the low power channel
is at a nominally low power level, as chosen in Figure 76. If the
inputs to both RF channels are at the same frequency, the isolation also depends on the phase shift between the RF signals put
into the AD8364. This can be seen by placing a high power
signal on one RF channel input and another signal (low power)
slightly offset in frequency to the other RF channel. If the output
of the low power channel is observed with an oscilloscope, it
would have a ripple that would look similar to a full-wave
rectified sine wave with a frequency equal to the frequency
difference between the two channels, that is, a beat tone. The
magnitude of the ripple reflects the isolation at a specific phase
offset (note that two signals of slightly different frequencies act
like two signals with a constantly changing phase), and the
frequency of that ripple is directly related to the frequency offset.
The data taken in Figure 76 assumes worst-case amplitude and
phase offset. If the RF signals on Channel A and Channel B are at
significantly different frequencies, the input-to-output isolation
increase, depending on the capacitors placed on CLP[A, B] and
CHP[A, B] and the frequency offset of the two signals (Figure 77),
due to the response roll-off within AD8364.
–40
–45
–50
–55
–60
–65
–70
ISOLATION (dB)
–75
–80
–85
–90
B->A
A->B
10,000101001,000
FREQUENCY (MHz)
Figure 75. RF Channel Input-to-Input Isolation
16
PEAK INTERFERENCE (IN dB) TO A–45dBm INPUT SIGNAL
DUE TO AN INTERFERING SIGNAL ON THE OTHER
CHANNEL. A->B = A INTERFERING WITH B, X-AXIS IS
14
CHANNEL A INPUT B->A = B INTERFERING WITH A, X-AXIS
IS CHANNEL B INPUT FREQUENCY SEPARATION OF THE
TWO CHANNELS = 1kHz. SEE CHARACTERIZATION
12
DESCRIPTION SECTION FOR MORE INFORMATION.
10
8
6
4
PEAK DEVIATION FROM
2
–45dBm EQUIVALENT OUTPUTS (dB)
0
A–>B 880MHz
B–>A 1880MHz
A–>B 1880MHz
B–>A 2140MHz
B–>A 2500 MHz
A–>B 2140MHz
A–>B
2500MHZ
INTERFERING CHANNEL AMPLITUDE (dBm)
B–>A 880MHz
A–>B
450 MHz
B–>A
450 MHz
15–20–10–150–5510
05334-022
Figure 76. Apparent Measurement Error Due to Overall Channel-to-Channel
Cross-Coupling
7
PEAK INTERFERENCE (IN dB) TO A -45dBm INPUT
SIGNAL DUE TO AN INTERFERING SIGNAL ON THE
6
OTHER CHANNEL.
A->B = A INTERFERING WITH B, X-AXIS IS CHANNEL A
5
INPUT Freq chA = 2500 MHz Freq CHB = 1880MHz
B->A = B INTERFERING WITH A, X-AXIS IS
4
CHANNEL B INPUT Freq CHB = 2500 MHz
Freq CHA = 1880 MHz
3
FREQUENCY SEPARATION OF THE
OUTPUT(dB)
TWO CHANNELS = 620 MHz.
SEE CHARCTERIZATION DESCRIPTION
2
SECTION FOR MORE INFORMATION
1
PEAK DEVIATION FROM -45dBm EQUIVALENT
0
–20–15–10–5051015
INTERFERING CHANNEL AMPLITUDE (dBm)
Figure 77. Improved Measurement Error with Increased Frequency
Separation
B->A
A->B
05334-085
05334-021
Rev. 0 | Page 35 of 48
Page 36
AD8364
CHOOSING THE RIGHT VALUE
FOR CHP[A, B] AND CLP[A, B]
The AD8364’s VGA includes an offset cancellation loop, which
introduces a high-pass filter effect in its transfer function. The
corner frequency, f
input signal in the desired measurement bandwidth frequency
to properly measure the amplitude of the input signal. The
required value of the external capacitor is given by
CHP[A, B] = 200 µF/(2 × π × f
Thus, for operation at frequencies down to 100 kHz, CHP[A, B]
should be 318 pF.
In the standard connections for the measurement mode, the
VST[A, B] pin is tied to OUT[A, B]. For small changes in input
amplitude (a few decibels), the time-domain response of this
loop is essentially linear with a 3 dB low-pass corner frequency
of nominally f
delays around this local loop set the minimum recommended
value of this capacitor to about 300 pF, making f
For operation at lower signal frequencies, or whenever the
averaging time needs to be longer, use
CLP[A, B] = 900 µF/2 × π × f
When the input signal exhibits large crest factors, such as a
WCDMA signal, CLP[A, B] must be much larger than might at
first seem necessary. This is due to the presence of significant low
frequency components in the complex, pseudo random modulation, which generates fluctuations in the output of the AD8364.
RF BURST RESPONSE TIME
RF burst response time is important for modulated signals that
have large steps in power, such as a single carrier EVDO that
has the potential for a greater than 20 dB burst of power (for
approximately 200 µs out of every 800 µs).
Accurate power detection for signals with RF bursts is achieved
when the AD8364 is able to respond quickly to the change in RF
power; however, the response time is limited by the capacitors
placed on Pins CLP[A, B], CHP[A, B], and DEC[A, B].
Capacitors placed on the DEC[A, B] pins affect the response time
the least and should be chosen as stated in the RF Input Interface
section. Capacitors placed on CHP[A, B] and CLP[A, B] should
be chosen according to the equations in the Choosing the Right
Value for CHP[A, B] and CLP[A, B] section and the response time
for the AD8364 should be evaluated. If the response time is not
fast enough to follow the burst response, the values for CLP[A, B]
should be decreased. The capacitor values placed on the CLP[A,
B] have the largest effect on the rise and fall times. The capacitor
values placed on CHP[A, B] affect the rising and falling corner
of the response (overshoot or under-shoot); however, the falling
corner is most likely swamped out by the effect of CLP[A, B].
, of this filter must be below that of the lowest
HP
)(fHP in Hz) (18)
HP
= 1/(2 × π × CLP[A, B] × 1.1 kΩ). Internal time
LP
= 482 kHz.
LP
(fLP in Hz) (19)
LP
Once the response time is set so that the AD8364 is just able to
follow the RF burst requirements (within the tolerance of the
capacitors), the output of the AD8364 should be evaluated with
an oscilloscope. If there is ripple on the output (due to the
modulated signal), averaging may need to be performed on
the DSP to achieve a true rms response. Figure 44 and Figure 45
may help in determining the proper CLP[A, B] values to use.
SINGLE-ENDED INPUT OPERATION
For optimum operation, the RF inputs to the AD8364 should be
driven differentially. However, the AD8364 RF inputs can also
be driven in a single-ended configuration with reduced
dynamic range. Figure 78 shows a recommended input
configuration for a single channel.
Figure 79 shows the performance obtained with the
configuration shown in Figure 78. The user should note that the
dynamic range performance suffers in single-ended
configuration due to the inherent amplitude and phase
imbalance at the RF inputs. However, at low frequency the
dynamic range is quite good and users trying to detect low
frequency or baseband signals may want to consider this as an
option. At frequencies greater than 450 MHz, the dynamic
range decreases to about 20 dB, reducing the AD8364’s
usefulness for many applications. Performance in single-ended
configuration is subject to circuit board layout (see the Printed
Circuit Board Considerations section).
INHx
100Ω
Figure 78. Recommended Input Configuration for Single-Ended Input Drive
5.0
4.5
4.0
3.5
3.0
2.5
2.0
OUTA (V)
1.5
1.0
0.5
0
50MHz Error
RF INPUT (dBm)
Figure 79. Single-Ended Performance for
the Configuration Shown in Figure 78
INLx
100Ω
450MHz ERROR
05334-044
50MHz
100MHz
45 MHz
100MHz ERROR
ERROR (dB)
20–60–40–30–50–20–10010
05334-045
Rev. 0 | Page 36 of 48
Page 37
AD8364
PRINTED CIRCUIT BOARD CONSIDERATIONS
Each RF input pin of the AD8364 presents 100 Ω impedance
relative to their respective ac grounds. To ensure that signal
integrity is not seriously impaired by the printed circuit board
(PCB), the relevant connection traces should provide
appropriate characteristic impedance to the ground plane. This
can be achieved through proper layout. When laying out an RF
trace with controlled impedance, consider the following:
•When calculating the RF line impedance, take into account
the spacing between the RF trace and the ground on the
same layer.
•Ensure that the width of the microstrip line is constant and
that there are as few discontinuities, such as component
pads, as possible along the length of the line. Width
variations cause impedance discontinuities in the line and
may result in unwanted reflections.
•Do not use silkscreen over the signal line because it can
alter the line impedance.
•Keep the length of the RF input traces as short as possible.
Figure 80 shows the cross section of a PC board, and Table 6
shows two possible sets of dimensions that provide a 100 Ω line
impedance for FR-4 board material with ε
board material with ε
= 3.38.
r
Table 6. Possible Trace Dimensions for Z
Dimension FR-4 (mil) Rodgers 4003 (mil)
W 22 6
H 53 11
T 2 0.7
W3W
H
E
R
Figure 80. Cross-Section View of a PC Board
It is possible to approximate a 100 Ω trace on a board designed
with the 50 Ω dimensions above by removing the ground plane
within three line widths of the area directly below the trace.
However, more predictable performance may be obtained with
precise ground plane spacing. It is possible to design a circuit
board with two ground planes, one plane for areas with 50 Ω
characteristic impedance and another for areas with 100 Ω
characteristic impedance. If the 100 Ω plane is placed below the
50 Ω plane, then an opening can be made in the 50 Ω plane to
allow the 100 Ω traces to work against the 100 Ω ground plane.
The two ground planes should be connected together with as
many vias as possible.
= 4.6 and Rodgers 4003
r
= 100 Ω
O
3W
T
05334-046
The accurate measurement range (that is, the dynamic range) of
AD8364’s detectors is sensitive to amplitude and phase matching
of the signals presented at the differential inputs. Care should be
taken to ensure matching of these parameters and to minimize
parasitic capacitance on the RF inputs when laying out the PC
board. It is also suggested that the two traces associated with
each differential input be mirror images, or duplicates, of one
another where possible. A high quality balun with known
output magnitude and phase characteristics is recommended to
perform single-ended to balanced conversions. It is possible to
improve the dynamic range by skewing the amplitude and
phase matching at the input. See the Typical Performance
Characteristics section for more details.
Stable, low ESR capacitors are mandatory in the RF circuitry of
the AD8364. This corresponds to capacitors connected to
Pins INH[A, B], INL[A, B], DEC[A, B], and CHP[A, B]. High
ESR capacitors may result in amplitude and phase mismatch at
the differential inputs, which in turn results in low dynamic
range. Capacitors with poor aging characteristics under
temperature cycling have been shown to accentuate the
temperature drift during operation of the AD8364. Use of
Samsung CL10 series multilayer ceramic capacitors (or similar)
in the RF area are recommended.
High transient and noise levels on the power supply, ground,
and inputs should be avoided. This reinforces the need for
proper supply bypassing and decoupling. See the Evaluation
Boards for suggestions.
A solder appropriate for either the lead-free or leaded version of
the AD8364 should be chosen. After the circuit board has been
soldered, it is important to thoroughly clean all excess solder
flux and residues from the board. Any residual material may act
as stray parasitic capacitance, which could result in degraded
performance.
PACKAGE CONSIDERATIONS
The AD8364 uses a compact 32-lead LFCSP. A large exposed
paddle on the bottom of the device provides both a thermal
benefit and a low inductance path to ground for the circuit. To
make proper use of this packaging feature, the PCB RF/dc
common ground reference needs to make contact directly
under the device with as many vias as possible to lower the
inductance and thermal impedance.
Rev. 0 | Page 37 of 48
Page 38
AD8364
(
)
−
A
DESCRIPTION OF CHARACTERIZATION
The general hardware configuration used for most of the
AD8362 characterization is shown in Figure 81. The signal
sources used in this example are the Rohde & Schwarz SMIQ03B
and Agilent E4438C. Input-matching baluns are used to transform
the single-ended RF signal to its differential form. Due to the
differential inputs’ sensitivity to amplitude and phase mismatch,
specific baluns were used for each characterization frequency to
achieve the best performance.
Other selected configurations are shown in Figure 82 and
Figure 83 as well.
SIGNAL
SOURCE
SIGNAL
SOURCE
–3dB
–3dB
INA
AD8364
CHARACTERIZATION
BOARD
INB
OUTA
OUTB
OUTP
OUTN
VREF
TEMP
AGILENT
34970A
METER/
SWITCHING
BASIS FOR ERROR CALCULATIONS
The slope and intercept are derived using the coefficients of a
linear regression performed on data collected in its central
operating range. Error is stated in two forms: (1) error from
linear response to CW waveform and (2) output delta from
25°C performance.
The error from linear response to CW waveform is the decibel
difference in output from the ideal output defined by the
conversions gain and output reference. This is a measure of the
linearity of the device response to both CW and modulated
waveforms. The error in dB is calculated by
PPSlopeV
−×
IN
Error (dB) =
where P
is the x-axis intercept expressed in dBm. This is
Z
OUT
Slope
analogous to the input amplitude that would produce an output
of 0 V, if such an output was possible.
Z
COMPUTER
CONTROLLER
Figure 81. General Characterization Configuration
GILENT 8648
RF SOURCE
–6dB SPLITTER
50Ω
–9dB
–8dB
AD8340 OR
AD8341 VECTOR
MODULATOR
Figure 82. Configuration for Amplitude and Phase Mismatch
Characterization
MINI-CIRCUITS
ZHL–42W
–8dB–6dB
–8dB–6dB
INHA/B
INLA/B
05334-047
05334-052
Error from the linear response to the CW waveform is not a
measure of absolute accuracy, since it is calculated using the
slope and intercept of each device. However, it verifies the
linearity and the effect of modulation on the device’s response.
Similarly, error from 25°C performance uses the 25°C
performance of a given device and waveform type as the
reference from which all other performance parameters shown
alongside it are compared. It is predominantly (and most often)
used as a measurement of output variation with temperature.
Rev. 0 | Page 38 of 48
Page 39
AD8364
VPOS
R24
0Ω
R5
0Ω
C8
0.1µF
AD8364ACPZ
C24
100pF
C13
0.1µF
C12
100pF
C15
CLPA
1819172021222423
VSTA
15
OUTA
14
FBKA
13
OUTP
12
OUTN
11
FBKB
10
OUTB
9
VSTB
76854312
C16
CLPB
05334-048
TEKTDS510
SCOPE
SMIQ06B
SIGNAL
GENERATOR
LECROY9213
PULSE
GENERATOR
3dB
HP6236B
POWER
SUPPLY
VPOS
R4
0Ω
BALUN
BALUN
R21
0Ω
VPOS
C23
100pF
C11
0.1µF
C9
0.1µFC90.1µF
C10
100pF
CHPACLPAACOMTEMPACOMVPSRCOMADECA
2516
VPSA
26
INHA
27
INLA
28
PWDN
29
COMR
30
INLB
31
INHB
32
VPSB
CHPBCLPBVLVLVREFADJAADJBCOMBDECB
C20
100pF
C22
0.1µF
C21
0.1µF
C1
0.1µF
Figure 83. Configuration for RF Burst Measurement
Rev. 0 | Page 39 of 48
Page 40
AD8364
EVALUATION AND CHARACTERIZATION
CIRCUIT BOARD LAYOUTS
There are two evaluation boards for the AD8364, one
appropriate for low frequency work (AD8364-EVAL-500) and
another one designed for use at 2140 MHz (AD8364-EVAL-
2140). Each board has a balun specific to operation in the
designated frequency range. The RF area layout of the circuit
board used for characterization work at 880 MHz is included in
this section, showing the footprint of the recommended balun
(Mini-Circuits JTX-4-10T) and trace lengths used. The user
may obtain different performance than shown in this data sheet
if their layout dimensions and style differ.
05334-092
Figure 84. AD8364-EVAL-500 Evaluation Board RF Area Layout
Rev. 0 | Page 40 of 48
Page 41
AD8364
05334-093
Figure 85. AD8364_EVAL-2140 Evaluation Board RF Area Layout
05334-050
Figure 86. 880 MHz Characterization Board RF Area Layout
R24, R23
R10, R11 Capacitors can be installed for controller mode. 0 Ω
R2, R16 Optional pull-down resistors. 10 kΩ/OPEN
R1, R3
R14 To be added for use in slope adjustment (not installed). OPEN
SW1
SW2, SW3
SW4 VLVL VREF (Position A)/external control (Position B) selector.
SW5 ADJA VREF (Position A)/external control (Position B) selector.
SW6 ADJB VREF (Position B)/external control (Position A) selector.
The dynamic range of the AD8364 is directly related to the
magnitude and phase balance of the balun feeding the RF
signal to the part. The evaluation board includes M/A-COM
ETK4-2T soldered to the board and two unsoldered M/A-COM
ETC1.6-4-2-3. The ETK4-2T has good magnitude and phase
balance between 10 MHz and 650 MHz, but slowly degrades
above 650 MHz due to the balun. The M/A-COM ETC1.6-4-2-3
broadband baluns allow limited dynamic range performance
between 500 MHz and 2500 MHz. Better dynamic range can be
achieved by using narrow band baluns with better magnitude
and phase performance.
Output low-pass filter capacitors, which can be activated by
removing jumpers R6 and R15.
Stable, low ESR capacitors are mandatory in the RF input area
of the AD8364. This corresponds to capacitors connected to
Pins INH[A, B], INL[A, B], DEC[A, B], and CHP[A, B]. Poor quality
capacitors may result in amplitude and phase mismatch at the
differential inputs, which in turn results in low dynamic range.
Capacitors with poor aging characteristics under temperature
cycling have been shown to accentuate the temperature drift
during operation of the AD8364. Using Samsung CL10 series
multilayer ceramic capacitors (or similar) in the RF area is
suggested.
R17/R19 are usually jumpers and R18/R20 are usually left open.
The pads for R17/R18 or R19/R20 can be used to make voltage
dividers to set the ADJA/B voltages for temperature
compensation at different frequencies.
R12 is usually a jumper and R13 is usually open, but the pads
can also be used to make a voltage divider to adjust the slope of
Channel B.
Jumpers. 0 Ω
100 Ω resistor to be added when input coupling from a singleended source (not installed).
Power-down/enable or external power-down selector, open is
enable (Position A, unloaded).
Measurement mode (Position A)/controller mode (Position B)
selector.
R21
R10, R11 Capacitors can be installed for controller mode. 0 Ω
R24 Optional loading resistor for TEMP. 1 kΩ
R2, R16 Optional pull-down resistors. OPEN
R14, R27 To be added for use in slope adjustment (not installed). OPEN
SW1
SW2, SW3
SW4 VLVL VREF (Position A)/external control (Position B) selector.
SW5 ADJA VREF (Position A)/external control (Position B)l selector.
SW6 ADJB VREF (Position B)/external control (Position A) selector.
The dynamic range of the AD8364 is directly related to the
magnitude and phase balance of the balun feeding the RF
signal to the part. At 2140 MHz, we have found it necessary to
use a narrow band balun and have used the Murata
LDB212G1020C-001.
Output low-pass filter capacitors, which can be activated by
removing jumpers R6 and R15.
Stable, low ESR capacitors are mandatory in the RF input area
of the AD8364. This corresponds to capacitors connected to
Pins INH[A, B], INL[A, B], DEC[A, B], and CHP[A, B]. Poor quality
capacitors may result in amplitude and phase mismatch at the
differential inputs, which in turn results in low dynamic range.
Capacitors with poor aging characteristics under temperature
cycling have been shown to accentuate the temperature drift
during operation of the AD8364. Using Samsung CL10 series
multilayer ceramic capacitors (or similar) in the RF area is
suggested.
R17/R19 are usually jumpers and R18/R20 are usually left open.
The pads for R17/R18 or R19/R20 can be used to make voltage
dividers to set the ADJA/B voltages for temperature
compensation at different frequencies.
Jumpers. 0 Ω
Power-down/enable or external power-down selector, open is
enable (Position A, unloaded).
Measurement mode (Position A)/controller mode (Position B)
selector.
Murata LDB212G1020C-00
0.1 µF
Samsung CL10B104KONC 0.1 µF
R17/R19 = 0 Ω
R18/R20 =
OPEN
Rev. 0 | Page 43 of 48
Page 44
AD8364
EVALUATION BOARDS
R23
0Ω
R4
0Ω
T2
INPA
PWDN
INPB
C5
ETK4-2T
0.1µF
J3
1:4
A
J2
SW1
B
VPOS
1:4
J1
C2
0.1µF
T1
ETK4-2T
10kΩ
R21
0Ω
COMM
R2
C4
0.1µF
C3
0.1µF
VPOS
TP1
TP2
C7
0.1µF
OPEN
C6
0.1µF
OPEN
R3
R1
VPOS
R24
0Ω
C23
100pF
C11
0.1µF
C9
0.1µFC90.1µF
C10
100pF
CHPACLPAACOMTEMPACOMVPSRCOMADECA
2516
VPSA
26
INHA
27
INLA
28
PWDN
29
COMR
C8
0.1µF
AD8364ACPZ
C13
R5
0.1µF
0Ω
C12
100pF
C14
0.1µF
TEMP
SENSOR
J4
1819172021222423
EXPOSED PADDLE
30
INLB
31
INHB
32
VPSB
CHPBCLPBVLVLVREFADJAADJBCOMBDECB
C20
100pF
C21
0.1µF
0.1µF
C22
0.1µF
C1
C24
100pF
R20
OPEN
R19
0Ω
SW6SW5
ABBA
R18
OPEN
R17
0Ω
C19
0.1µF
R16
OPEN
SW4
AAB
76854312
OPEN
C18
VREF
C15
0.1µF
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
0.1µF
C17
R6
0Ω
SETPOINT
VOLTAGE A
B
A
B
J5
OUTPUT
VOLTAGE A
J6
DIFF OUT +
J7
DIFF OUT +
J8
OUTPUT
VOLTAGE B
J9
SETPOINT
VOLTAGE B
J10
SW2
R9
R14
OPEN
C16
0.1µF
0Ω
R12
0Ω
SW3
15
R10
0Ω
14
13
12
R11
0Ω
11
10
9
R13
OPEN
R15
0Ω
ADJB
J13
ADJA
J12
REF LEVEL
VOLTAGE
J11
Figure 87. AD8364-EVA-500 Evaluation Board
Rev. 0 | Page 44 of 48
05334-051
Page 45
AD8364
C23
100pF
C11
0.1µF
R4
INPA
PWDN
INPB
J3
J2
J1
C5
LDB212G1020C
0.1µF
1:4
A
SW1
B
VPOS
1:4
C2
0.1µF
LDB212G1020C
0Ω
T2
C7
0.1µF
OPEN
C6
0.1µF
C4
0.1µF
C3
0.1µF
T1
R21
0Ω
VPOS
TP1
COMM
TP2
C9
0.1µFC90.1µF
C10
100pF
R3
CHPACLPAACOMTEMPACOMVPSRCOMADECA
2516
VPSA
26
INHA
27
INLA
28
PWDN
29
COMR
30
INLB
31
INHB
32
VPSB
CHPBCLPBVLVLVREFADJAADJBCOMBDECB
C20
100pF
C21
0.1µF
0.1µF
C22
0.1µF
C1
C24
100pF
VPOS
R5
0Ω
C8
0.1µF
AD8364ACPZ
EXPOSED PADDLE
R19
0Ω
SW6SW5
C13
0.1µF
C12
100pF
R24
1kΩ
R20
R18
OPEN
OPEN
R17
0Ω
ABBA
C19
0.1µF
R16
OPEN
SW4
C14
0.1µF
TEMP
SENSOR
J4
1819172021222423
76854312
OPEN
AAB
C18
C15
0.1µF
VSTA
OUTA
FBKA
OUTP
OUTN
FBKB
OUTB
VSTB
C17
0.1µF
R6
0Ω
VREF
B
A
B
SETPOINT
VOLTAGE A
J5
OUTPUT
VOLTAGE A
J6
DIFF OUT +
J7
DIFF OUT –
J8
OUTPUT
VOLTAGE B
J9
SETPOINT
VOLTAGE B
J10
R27
OPEN
SW2
R9
R14
OPEN
0Ω
R12
0Ω
SW3
15
R10
0Ω
14
13
12
R11
0Ω
11
10
9
VREF
R15
0Ω
C16
0.1µF
VREF
ADJB
J13
ADJA
J12
REF LEVEL
VOLTAGE
J11
Figure 88. AD8364-EVAL-2140 Evaluation Board
Rev. 0 | Page 45 of 48
05334-097
Page 46
AD8364
ASSEMBLY DRAWINGS
05334-096
Figure 89. AD8364-EVAL-500 Assembly Drawing
05334-098
Figure 90. AD8364-EVAL-2140 Assembly Drawing
Rev. 0 | Page 46 of 48
Page 47
AD8364
OUTLINE DIMENSIONS
5.00
PIN 1
INDICATOR
1.00
0.85
0.80
12° MAX
SEATING
PLANE
BSC SQ
TOP
VIEW
0.80 MAX
0.65 TYP
0.30
0.23
0.18
COMPLIANT TO JEDEC STANDARDS MO-220-VHHD-2
4.75
BSC SQ
0.20 REF
0.05 MAX
0.02 NOM
0.60 MAX
0.50
BSC
0.50
0.40
0.30
COPLANARITY
0.08
Figure 91. 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
5 mm × 5 mm Body, Very Thin Quad
(CP-32-3)
Dimensions shown in millimeters
ORDERING GUIDE
Model Temperature Range Package Description Package Option
AD8364ACPZ-WP
AD8364ACPZ-REEL71 −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-32-3 1,500 Units
AD8364ACPZ-RL21 −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-32-3 250 Units
AD8364ACP-REEL7 −40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-32-3 1,500 Units
AD8364-EVAL-500 Evaluation Board, Low Frequency to 500 MHz
AD8364-EVAL-2140 Evaluation Board, 2140 MHz only
1
Z = Pb-free part.
2
WP = Waffle Pack
1, 2
−40°C to +85°C 32-Lead Lead Frame Chip Scale Package [LFCSP_VQ] CP-32-3 36 Units