Analog Devices AD641AP, AD641AN, AD641-EB, 5962-9559801MRA Datasheet

250 MHz Demodulating

a

FEATURES
Logarithmic Amplifier Performance

Usable to 250 MHz
44 dB Dynamic Range
ⴞ2.0 dB Log Conformance

37.5 mV/dB Voltage Output
Stable Slope and Intercepts

2.0 nV/√Hz Input Noise Voltage

50 ␮V Input Offset Voltage
Low Power

ⴞ5 V Supply Operation

9 mA (+V
Onboard Resistors
Onboard 10ⴛ Attenuator
Dual Polarity Current Outputs
Direct Coupled Differential Signal Path

APPLICATIONS
IF/RF Signal Processing
Received Signal Strength Indicator (RSSI)
High Speed Signal Compression
High Speed Spectrum Analyzer
ECM/Radar

PRODUCT DESCRIPTION

The AD641 is a 250 MHz, demodulating logarithmic amplifier

with an accuracy of ±2.0 dB and 44 dB dynamic range. The

AD641 uses a successive detection architecture to provide an
output current that is logarithmically proportional to its input
voltage. The output current can be converted to a voltage using
one of several on-chip resistors to select the slope. A single
AD641 provides up to 44 dB of dynamic range at speeds up to
250 MHz, and two cascaded AD641s together can provide
58 dB of dynamic range at speeds up to 250 MHz. The AD641
is fully stable and well characterized over either the industrial or
military temperature ranges.

The AD641 is not a logarithmic building block, but rather a
complete logarithmic solution for compressing and measuring
wide dynamic range signals. The AD641 is comprised of five
stages and each stage has a full wave rectifier, whose current
depends on the absolute value of its input voltage. The output
of these stages are summed together to provide the demodulated

output current scaled at 1 mA per decade (50 µA/dB).
Without utilizing the 10× input attenuator, log conformance of

2.0 dB is maintained over the input range –44 dBm to 0 dBm.
The attenuator offers the most flexibility without significantly
impacting performance.

), 35 mA (–VS) Quiescent Current

S

Logarithmic Amplifier

AD641

PIN CONFIGURATIONS

20-Lead Plastic DIP (N)

20-Lead Cerdip (Q)

–INPUT

+INPUT

PIN 1
IDENTIFIER

S

+V

SIG +OUT

20

+INPUT

19

ATN OUT

18

17

RG1

16

RG0

15

RG2

14

LOG OUT

13

LOG COM

12

+V

S

11

+OUTPUT

ATN OUT

18
17
16
15
14

LOG COM

CKT COM
RG1
RG0
RG2
LOG OUT

1

–INPUT

2

ATN LO

ATN IN

BL1
–V

ITC

BL2

3

4

5

6

7

S

8

9

10

AD641

TOP VIEW

(Not to Scale)

ATN COM CKT COM
ATN COM

–OUTPUT

20-Lead PLCC (P)

ATN COM

ATN LO

3 2 1 20 19

ATN IN

BL1
–V

ITC

4
5
6
7

S

8

AD641

TOP VIEW

(Not to Scale)

9 10 11 12 13

BL2

SIG –OUT

ATN COM

The 250 MHz bandwidth and temperature stability make this
product ideal for high speed signal power measurement in RF/
IF systems. ECM/Radar and Communication applications are
routinely in the 100 MHz–180 MHz range for power measure­ment. The bandwidth and accuracy, as well as dynamic range,
make this part ideal for high speed, wide dynamic range signals.

The AD641 is offered in industrial (–40°C to +85°C) and mili­tary (–55°C to +125°C) package temperature ranges. Industrial

versions are available in plastic DIP and PLCC; MIL versions
are packaged in cerdip.

REV. C

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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: [phone] World Wide Web Site: http://www.analog.com
Fax: [phone] © Analog Devices, Inc., 1999

AD641–SPECIFICATIONS

ELECTRICAL CHARACTERISTICS

(VS = ⴞ5 V; TA = +25ⴗC, unless otherwise noted)

AD641A AD641S

Parameter Conditions Min Typ Max Min Typ Max Units

TRANSFER FUNCTION

1

(I

= IY LOG |VIN/VX|for V

OUT

= 0.75 mV to ±200 mV dc)

IN

LOG AMPLIFIER PERFORMANCE

3 dB Bandwidth 250 250 MHz
Voltage Compliance Range –0.3 +V
Slope Current, I

Y

0.98 1.00 1.02 0.98 1.00 1.02 mA

– 1 –0.3 +VS – 1 V

S

Accuracy vs. Temperature 0.002 0.002 %/°C

Over Temperature T

MIN

to T

MAX

0.98 1.02 mA

Intercept dBm 250 MHz –40.84 –40.43 –39.96 –40.84 –40.43 –39.96 dBm

Over Temperature T

Zero Signal Output Current

2

MIN

to T

250 MHz –40.59 –39.47 dBm

MAX,

–0.2 –0.2 mA

ITC Disabled Pin 8 to COM –0.27 –0.27 mA

Maximum Output Current 2.3 2.3 mA

DYNAMIC RANGE

Single Configuration 44 44 dB

Over Temperature T

MIN

to T

MAX

40 38 dB

Dual Configuration 58 58 dB

Over Temperature T

MIN

to T

MAX

52 52 dB

LOG CONFORMANCE f = 250 MHz

Single Configuration –44 dBm to 0 dBm ±0.5 ±2.0 ±0.5 ±2.0 dB

Over Temperature –42 dBm to –4 dBm; T

–42 dBm to –2 dBm, T

MIN

MIN

to T
to T

MAX

MAX

±1.0 ±2.5

±1.0 ±2.5 dB

Dual Configuration S: –60 dBm to –2 dBm; ±0.5 ±2.0 ±0.5 ±2.0 dB

Over Temperature A: –56 dBm to –4 dBm, T

MIN

to T

MAX

±1.0 ±2.5 ±1.0 ±2.5 dB

LIMITER CHARACTERISTICS

Flatness –44 dBm to 0 dBm @ 10.7 MHz ±1.6 ±1.6 dB
Phase Variation –44 dBm to 0 dBm @ 10.7 MHz ±2.0 ±2.0 Degrees

INPUT CHARACTERISTICS

Input Resistance Differential 500 500 kΩ
Input Offset Voltage Differential 50 200 50 200 µV

vs. Temperature 0.8 0.8 µV/°C

Over Temperature T

MIN

to T

MAX

300 µV

vs. Supply 22µV/V
Input Bias Current 7 25 7 25 µA
Input Bias Offset 11µA

Common Mode Input Range –2 +0.3 –2 +0.3 V

SIGNAL INPUT (Pins 1, 20)

Input Capacitance Either Pin to COM 2 2 pF

Noise Spectral Density 1 kHz to 10 MHz 2 2 nV/√Hz

Tangential Sensitivity BW = 100 MHz –72 –72 dBm

INPUT ATTENUATOR

(Pins 2, 3, 4, 5 & 19)

Attenuation

3

Pins 5 to Pin 19 20 20 dB

Input Resistance Pins 5 to 3/4 300 300 Ω

APPLICATION RESISTORS

(Pins 15, 16, 17) 0.995 1.000 1.005 0.995 1.000 1.005 kΩ

OUTPUT CHARACTERISTICS

(Pins 10, 11)

Peak Differential Output

4

±180 ±180 mV

Output Resistance Either Pin to COM 75 75 Ω

Quiescent Output Voltage Either Pin to COM –90 –90 mV

POWER SUPPLY

Voltage Supply Range ±4.5 ±7.5 ±4.5 ±7.5 V

Quiescent Current

(Pin 12) T

+V

S

–VS (Pin 7) T

NOTES

1

Logarithms to base 10 are used throughout. The response is independent of the sign of VIN.

2

The zero-signal current is a function of temperature unless internal temperature compensation (ITC) pin is grounded.

3

Attenuation ratio trimmed to calibrate intercept to 10 mV when in use. It has a temperature coefficient of +0.3%/°C.

4

The fully limited signal output will appear to be a square wave; its amplitude is proportional to absolute temperature.

Specifications subject to change wi

thout notice.

MIN

MIN

to T
to T

MAX

MAX

915 9 15 mA
35 60 35 60 mA

–2–

REV. C

AD641

WARNING!

ESD SENSITIVE DEVICE

ORDERING GUIDE

Temperature Package Package

Model Range Description Option

AD641AN –40°C to +85°C Plastic DIP N-20

AD641AP –40°C to +85°C PLCC P-20A

5962-9559801MRA –55°C to +125°C Cerdip Q-20

AD641-EB Evaluation Board

ABSOLUTE MAXIMUM RATINGS*

Supply Voltages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±7.5 V

Input Voltage (Pin 1 or Pin 20 to COM) . . . –3 V to +300 mV

Attenuator Input Voltage (Pin 5 to Pin 3/4) . . . . . . . . . . . ±4 V

Storage Temperature Range, Q . . . . . . . . . . –65°C to +150°C

Storage Temperature Range, N, P . . . . . . . . –65°C to +125°C

Ambient Temperature Range, Rated Performance

Industrial, AD641A . . . . . . . . . . . . . . . . . . –40°C to +85°C

Military, AD641S . . . . . . . . . . . . . . . . . . –55°C to +125°C

THERMAL CHARACTERISTICS

␪

JC

␪

(ⴗC/W) (ⴗC/W)

20-Lead Plastic DIP Package (N) 24 61

JA

Lead Temperature Range (Soldering 60 sec) . . . . . . . . +300°C

*Stresses above those listed under Absolute Maximum Ratings may cause perma-

nent 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 adversely affect device reliability.

20-Lead Cerdip Package (Q) 25 85

20-Lead Plastic Leadless Chip Carrier (P) 28 75

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 the AD641 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. C

–3–

AD641

(

)

4.5 5.0 5.5 6.0 6.5 7.0 7.5
POWER SUPPLY VOLTAGES – 6 Volts

SLOPE CURRENT – mV

1.006

1.004

1.002

1.000

0.998

0.996

0.994

–Typical DC Performance Characteristics

1.015

1.010

1.005

1

0.995

0.990

SLOPE CURRENT – mA

0.985

0.980
–60 –40 –20 0 20 40 60 80 100 120 140

TEMPERATURE – 8C

Figure 1. Slope Current, IY, vs.

Temperature

1.015

1.010

1.005

1.000

0.995

0.990

INTERCEPT VOLTAGE – mV

0.985

4.5 5.0 5.5 6.0 6.5 7.0 7.5
POWER SUPPLY VOLTAGES – 6 Volts

Figure 4. Intercept Voltage, VX, vs.
Supply Voltages

1.20

1.15

1.10

1.05

1.00

INTERCEPT – mV

0.95

0.90

0.85
–60 –40 –20 0 20 40 60 80 100 120 140

TEMPERATURE – 8C

Figure 2. Intercept Voltage, VX, vs.
Temperature

14

13

12

11

10

INTERCEPT – mV

9

8

7
–60 –40 –20 0 20 40 60 80 100 120 140

TEMPERATURE – 8C

Figure 5. Intercept Voltage (Using
Attenuator) vs. Temperature

Figure 3. Slope Current, IY, vs. Supply
Voltages

+0.4

+0.3

+0.2

+0.1

0

–0.1

–0.2

–0.3

–60 –40 –20 0 20 40 60 80 100 120 140

DEVIATION OF INPUT OFFSET VOLTAGE – mV

INPUT OFFSET VOLTAGE
DEVIATION WILL BE WITHIN
SHADED AREA.

TEMPERATURE – 8C

Figure 6. Input Offset Voltage Devia­tion vs. Temperature

2.4

2.2

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

OUTPUT CURRENT – mA

0
–0.2
–0.4

0.1 1.0 1000.010.0 100.0

Figure 7. DC Logarithmic Transfer
Function and Error Curve for Single
AD641

INPUT VOLTAGE – mV

EITHER SIGN

2
1
0

ERROR – dB

2.5

2.0

1.5

1.0

ABSOLUTE ERROR – dB

0.5

0
–60 –40 –20 0 20 40 60 80 100 120 140

TEMPERATURE – 8C

Figure 8. Absolute Error vs. Tempera­ture, V

= ±1 mV to ±100 mV

IN

–4–

2.5

2.0

1.5

1.0

ABSOLUTE ERROR – dB

0.5

0
–60 –40 –20 0 20 40 60 80 100 120 140

TEMPERATURE – 8C

Figure 9. Absolute Error vs. Tempera­ture, Using Attenuator. V

±

1 V, Pin 8 Grounded to Disable ITC

to

= ±10 mV

IN

Bias

REV. C

Typical AC Performance Characteristics–

AD641

–2.25
–2.00
–1.75
–1.50
–1.25
–1.00
–0.75
–0.50

OUTPUT CURRENT – mA

–0.25

0.00

0.25
–52 –36 –32 –28 –24 –20 –16 –12 –8 0

–40

INPUT LEVEL – dBm

50MHz
150MHz

190MHz
210MHz
250MHz

2–48 –44

–4

Figure 10. AC Response at 50 MHz, 150 MHz, 190 MHz,
210 MHz at 250 MHz, vs. dBm Input (Sinusoidal Input)

87.5

85.0

82.5

80.0

–2.00
–1.75
–1.50
–1.25
–1.00
–0.75
–0.50

OUTPUT – mA

–0.25

+1258C

–0.00

0.25

0.50
–52 –36 –32 –28 –24 –20 –16 –12 –8 0

–558C

–558C

+1258C

+258C

ERROR

OUTPUT

+258C

–40

INPUT LEVEL – dBm

+258C

+1258C

+258C

–558C

+1258C

–558C

–4

5
4
3
2
1
0
–1
–2
–3
–4
–5

2–48 –44

Figure 13. Logarithmic Response and Linearity at
200 MHz, T

1.0

0.95

0.90

for TA = –55°C, +25°C, +125°C

A

ERROR IN – dB

77.5

75.0

INTERCEPT LEVEL – dBm

72.5

70.0
50 250100 150 170 190 210 230

INPUT FREQUENCY – MHz

Figure 11. Intercept Level (dBm) vs. Frequency (Cascaded
AD641s—Sinusoidal Input)

Figure 12. Baseband Pulse Response of Single AD641,
Inputs of 1 mV, 10 mV and 100 mV

0.85

SLOPE CURRENT – mA

0.80

0.75
50 250150 190 210

INPUT FREQUENCY – MHz

Figure 14. Slope Current, IY, vs. Input Frequency

5µs

100

90

10

0%

20mV

5µs

20mV

Figure 15. Baseband Pulse Response of Cascaded AD641s
at Inputs of 0.2 mV, 2 mV, 20 mV and 200 mV

REV. C

–5–