ANALOG DEVICES ADA4938-1, ADA4938-2 Service Manual
Ultralow Distortion
–
www.BDTIC.com/ADI
FEATURES
Extremely low harmonic distortion
−106 dBc HD2 @ 10 MHz
−82 dBc HD2 @ 50 MHz
−109 dBc HD3 @ 10 MHz
−82 dBc HD3 @ 50 MHz
Low input voltage noise: 2.6 nV/√Hz
High speed
−3 dB bandwidth of 1000 MHz, G = +1
Slew rate: 4700 V/μs
0.1 dB gain flatness to 150 MHz
Fast overdrive recovery of 4 ns
1 mV typical offset voltage
Externally adjustable gain
Differential-to-differential or single-ended-to-differential
oper
ation
Adjustable output common-mode voltage
Wide supply voltage range: +5 V to ±5 V
Single or dual amplifier configuration available
APPLICATIONS
ADC drivers
Single-ended-to-differential converters
IF and baseband gain blocks
Differential buffers
Line drivers
GENERAL DESCRIPTION
The ADA4938 is a low noise, ultralow distortion, high speed
differential amplifier. It is an ideal choice for driving high
performance ADCs with resolutions up to 16 bits from dc to
27 MHz, or up to 12 bits from dc to 74 MHz. The output commonmode voltage is adjustable over a wide range, allowing the ADA4938
to match the input of the ADC. The internal common-mode
feedback loop also provides exceptional output balance as well
as suppression of even-order harmonic distortion products.
Full differential and single-ended-to-differential gain configurations
re easily realized with the ADA4938. A simple external feedback
a
network of four resistors determines the closed-loop gain of the
amplifier.
The ADA4938 is fabricated using the Analog Devices, Inc.
p
roprietary third-generation, high voltage XFCB process, enabling
it to achieve very low levels of distortion with an input voltage
noise of only 2.6 nV/√Hz. The low dc offset and excellent dynamic
performance of the ADA4938 make it well suited for a wide
variety of data acquisition and signal processing applications.
Differential ADC Driver
ADA4938-1/ADA4938-2
FUNCTIONAL BLOCK DIAGRAMS
S
S
S
S
–V
–V
–V
–V
14
13
15
16
ADA4938-1
1–FB
2+IN
3–IN
4+FB
5
6
S
S
+V
+V
Figure 1. ADA4938-1 Functional Block Diagram
1
N1
–FB
+I
23
24
1–IN1
2+FB1
3+V
S1
ADA4938-2
4+V
S1
5–FB2
6+IN2
7
8
2
–IN2
+FB
Figure 2. ADA4938-2 Functional Block Diagram
50
–60
–70
–80
–90
SFDR (dBc)
–100
–110
–120
–130
G = +2, V
G = +2, V
G = +2, V
G = +2, V
1 10 100
= 5V p-p
O, dm
= 3.2V p-p
O, dm
= 2V p-p
O, dm
= 1V p-p
O, dm
FREQUENCY (MHz )
Figure 3. SFDR vs. Freque
The ADA4938-1 (single amplifier) is available in a Pb-free,
3 mm × 3 mm, 16-lead LFCSP. The ADA4938-2 (dual
amplifier) is available in a Pb-free, 4 mm × 4 mm, 24-lead
LFCSP. The pinouts have been optimized to facilitate layout and
minimize distortion. The parts are specified to operate over the
extended industrial temperature range of −40°C to +85°C.
12 PD
11 –OUT
10 +OUT
9V
OCM
8
7
S
S
+V
+V
S1
S1
D1
–V
–V
P
–OUT1
20
19
21
22
9
11
12
10
S2
S2
CM2
+V
+V
O
V
+OUT2
18 +O UT1
17 V
OCM1
16 –V
S2
–V
15
S2
14
PD2
13 –O UT2
06592-001
6592-202
ncy and Output Voltage
06592-002
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700 www.analog.com
Fax: 781.461.3113 ©2007 Analog Devices, Inc. All rights reserved.
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
General Description .........................................................................1
Functional Block Diagrams............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Dual-Supply Operation ............................................................... 3
Single-Supply Operation ............................................................. 5
Absolute Maximum Ratings............................................................ 7
Thermal Resistance ...................................................................... 7
ESD Caution.................................................................................. 7
Pin Configurations and Function Descriptions ...........................8
Typical Performance Characteristics............................................. 9
Test Circ uts ...................................................................................... 17
Operational Description................................................................ 18
Definition of Terms.................................................................... 18
Theory of Operation ...................................................................... 19
Analyzing an Application Circuit............................................ 19
Setting the Closed-Loop Gain .................................................. 19
Estimating the Output Noise Voltage...................................... 19
The Impact of Mismatches in the Feedback Networks......... 20
Calculating the Input Impedance of an
Application Circuit..................................................................... 20
Input Common-Mode Voltage Range in Single-Supply
Applications................................................................................ 20
Terminating a Single-Ended Input .......................................... 21
Setting the Output Common-Mode Voltage.......................... 21
Layout, Grounding, and Bypassing.............................................. 23
High Performance ADC Driving ................................................. 24
Outline Dimensions .......................................................................25
Ordering Guide .......................................................................... 25
REVISION HISTORY
11/07—Revision 0: Initial Version
Rev. 0 | Page 2 of 28
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
SPECIFICATIONS
DUAL-SUPPLY OPERATION
TA = 25°C, +VS = 5 V, −VS = −5 V, V
All specifications refer to single-ended input and differential output, unless otherwise noted. For gains other than G = 1, values for R
R
are shown in Ta ble 11.
G
= 0 V, RT = 61.9 , RG = RF = 200 , G = +1, R
OCM
= 1 kΩ, unless otherwise noted.
L, dm
and
F
Table 1. ±D
to ±OUT Performance
IN
Parameter Conditions Min Typ Max Unit
DYNAMIC PERFORMANCE
−3 dB Small Signal Bandwidth V
Bandwidth for 0.1 dB Flatness V
Large Signal Bandwidth V
Slew Rate V
= 0.1 V p-p 1000 MHz
OUT
= 2 V p-p 150 MHz
OUT
= 2 V p-p 800 MHz
OUT
= 2 V p-p 4700 V/μs
OUT
Overdrive Recovery Time VIN = 5 V to 0 V step, G = +2 4 ns
NOISE/HARMONIC PERFORMANCE
Second Harmonic V
V
Third Harmonic V
V
= 2 V p-p, 10 MHz −106 dBc
OUT
= 2 V p-p, 50 MHz −82 dBc
OUT
= 2 V p-p, 10 MHz −109 dBc
OUT
= 2 V p-p, 50 MHz −82 dBc
OUT
IMD f1 = 30.0 MHz, f2 = 30.1 MHz 89 dBc
IP3 f = 30 MHz, R
= 100 Ω 45 dBm
L, dm
Input Voltage Noise f = 10 MHz 2.6 nV/√Hz
Noise Figure G = +4, f = 10 MHz 15.8 dB
Input Current Noise f = 10 MHz 4.8 pA/√Hz
Crosstalk (ADA4938-2) f = 100 MHz −85 dB
INPUT CHARACTERISTICS
Offset Voltage V
T
OS, dm
MIN
= V
to T
/2; V
= V
OUT, dm
variation ±4 μV/°C
MAX
DIN+
= 0 V 1 4 mV
DIN−
Input Bias Current −18 −13 μA
T
MIN
to T
variation −0.01 μA/°C
MAX
Input Resistance Differential 6 MΩ
Common mode 3 MΩ
Input Capacitance 1 pF
Input Common-Mode Voltage
CMRR ∆V
OUT, dm
/∆V
IN, cm
; ∆V
= ±1 V, f = 1 MHz −75 dB
IN, cm
−V
+V
S
S
+ 0.3 to
− 1.6
V
OUTPUT CHARACTERISTICS
Output Voltage Swing Maximum ∆V
; single-ended output
OUT
−V
+V
S
S
+ 1.2 to
− 1.2
V
Linear Output Current Per amplifier 95 mA
Output Balance Error ∆V
OUT, cm
/∆V
OUT, dm
; ∆V
= 1 V; f = 10 MHz −60 dB
OUT, dm
Rev. 0 | Page 3 of 28
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
Table 2. V
Parameter Conditions Min Typ Max Unit
V
DYNAMIC PERFORMANCE
OCM
−3 dB Bandwidth 230 MHz
Slew Rate VIN = −3.4 V to +3.4 V, 25% to 75% 1700 V/μs
Input Voltage Noise (RTI) 7.5 nV/√Hz
V
INPUT CHARACTERISTICS
OCM
Input Voltage Range
Input Resistance 10 kΩ
Input Offset Voltage V
Input Bias Current 0.5 μA
V
OCM
Gain ∆V
POWER SUPPLY
Operating Range 4.5 11 V
Quiescent Current Per amplifier 37 40 mA
T
Powered down 2.0 3.0 mA
Power Supply Rejection Ratio ∆V
POWER DOWN (PD)
PD Input Voltage
Enabled ≥3 V
Turn-Off Time 1 μs
Turn-On Time 200 ns
PD Bias Current
Enabled
Disabled
OPERATING TEMPERATURE RANGE −40 +85 °C
to ±OUT Performance
OCM
CMRR ∆V
Powered down ≤2.5 V
PD
PD
+ 1.3 to
−V
S
− 1.3
+V
S
OS, cm
OUT, dm
OUT, cm
to T
MIN
OUT, dm
= 5 V
= −5 V
= V
; V
= V
OUT, cm
DIN+
/∆V
; ∆V
OCM
OCM
/∆V
; ∆V
OCM
OCM
variation 40 μA/°C
MAX
= 0 V 3 mV
DIN−
= ±1 V −81 dB
= ±1 V 0.95 1.00 1.05 V/V
/∆VS; ∆VS = ±1 V −80 dB
1 μA
−760 μA
V
Rev. 0 | Page 4 of 28
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
SINGLE-SUPPLY OPERATION
TA = 25°C, +VS = 5 V, −VS = 0 V, V
All specifications refer to single-ended input and differential output, unless otherwise noted. For gains other than G = 1, values for R
R
are shown in Ta ble 11.
G
= +VS/2, RT = 61.9 , RG = RF = 200 , G = +1, R
OCM
= 1 kΩ, unless otherwise noted.
L, dm
and
F
Table 3. ±D
to ±OUT Performance
IN
Parameter Conditions Min Typ Max Unit
DYNAMIC PERFORMANCE
−3 dB Small Signal Bandwidth V
Bandwidth for 0.1 dB Flatness V
Large Signal Bandwidth V
Slew Rate V
= 0.1 V p-p 1000 MHz
OUT
= 2 V p-p 150 MHz
OUT
= 2 V p-p 750 MHz
OUT
= 2 V p-p 3900 V/μs
OUT
Overdrive Recovery Time VIN = 2.5 V to 0 V step, G = +2 4 ns
NOISE/HARMONIC PERFORMANCE
Second Harmonic V
V
Third Harmonic V
V
= 2 V p-p, 10 MHz −110 dBc
OUT
= 2 V p-p, 50 MHz −79 dBc
OUT
= 2 V p-p, 10 MHz −100 dBc
OUT
= 2 V p-p, 50 MHz −79 dBc
OUT
Input Voltage Noise f = 10 MHz 2.6 nV/√Hz
Noise Figure G = +4, f = 10 MHz 15.8 dB
Input Current Noise f = 10 MHz 4.8 pA/√Hz
Crosstalk (ADA4938-2) f = 100 MHz −85 dB
INPUT CHARACTERISTICS
Offset Voltage V
T
OS, dm
MIN
= V
to T
/2; V
= V
= V
OUT, dm
variation ±4 μV/°C
MAX
DIN+
DIN−
= 2.5 V 1 4 mV
OCM
Input Bias Current −18 −13 μA
T
MIN
to T
variation −0.01 μA/°C
MAX
Input Resistance Differential 6 MΩ
Common mode 3 MΩ
Input Capacitance 1 pF
Input Common-Mode Voltage
CMRR ∆V
OUT, dm
/∆V
IN, cm
; ∆V
= ±1 V −80 dB
IN, cm
−V
+V
+ 0.3 to
S
− 1.6
S
V
OUTPUT CHARACTERISTICS
Output Voltage Swing Maximum ∆V
; single-ended output
OUT
−V
+V
+ 1.2 to
S
− 1.2
S
V
Linear Output Current Per amplifier 95 mA
Output Balance Error ∆V
OUT, cm
/∆V
OUT, dm
; ∆V
= 1 V −60 dB
OUT, dm
Rev. 0 | Page 5 of 28
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
Table 4. V
Parameter Conditions Min Typ Max Unit
V
DYNAMIC PERFORMANCE
OCM
−3 dB Bandwidth 400 MHz
Slew Rate VIN = 1.6 V to 3.4 V, 25% to 75% 1700 V/μs
Input Voltage Noise (RTI) 7.5 nV/√Hz
V
INPUT CHARACTERISTICS
OCM
Input Voltage Range
Input Resistance 10 kΩ
Input Offset Voltage V
Input Bias Current 0.5 μA
V
OCM
Gain ∆V
POWER SUPPLY
Operating Range 4.5 11 V
Quiescent Current 34 36.5 mA
T
Powered down 1.0 1.7 mA
Power Supply Rejection Ratio ∆V
POWER DOWN (PD)
PD Input Voltage
Enabled ≥3 V
Turn-Off Time 1 μs
Turn-On Time 200 ns
PD Bias Current
Enabled
Disabled
OPERATING TEMPERATURE RANGE −40 +85 °C
to ±OUT Performance
OCM
CMRR ∆V
Powered down ≤2.5 V
PD
PD
+ 1.3 to
−V
S
− 1.3
+V
S
OS, cm
OUT, dm
OUT, cm
to T
MIN
OUT, dm
= 5 V
= 0 V
= V
; V
= V
= V
OUT, cm
DIN+
DIN–
/∆V
; ∆V
OCM
/∆V
OCM
variation 40 μA/°C
MAX
= ±1 V −89 dB
OCM
; ∆V
= ±1 V 0.95 1.00 1.05 V/V
OCM
= 2.5 V 3 mV
OCM
/∆VS; ∆VS = ±1 V −80 dB
1 μA
−260 μA
V
Rev. 0 | Page 6 of 28
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
ABSOLUTE MAXIMUM RATINGS
Table 5.
Parameter Rating
Supply Voltage 12 V
Power Dissipation See Figure 4
Storage Temperature Range −65°C to +125°C
Operating Temperature Range −40°C to +85°C
Lead Temperature (Soldering, 10 sec) 300°C
Junction Temperature 150°C
Stresses above those listed under Absolute Maximum Rating
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.
THERMAL RESISTANCE
θJA is specified for the device (including exposed pad) soldered
to a high thermal conductivity 4-layer circuit board, as described in
EIA/JESD 51-7. The exposed pad is not electrically connected to
the device. It is typically soldered to a pad on the PCB that is
thermally and electrically connected to an internal ground plane.
Table 6. Thermal Resistance
Package Type θ
JA
16-Lead LFCSP (Exposed Pad) 95 °C/W
24-Lead LFCSP (Exposed Pad) 65 °C/W
Maximum Power Dissipation
The maximum safe power dissipation in the ADA4938 package
is limited by the associated rise in junction temperature (T
the die. At approximately 150°C, which is the glass transition
temperature, the plastic changes its properties. Even temporarily
exceeding this temperature limit can change the stresses that the
package exerts on the die, permanently shifting the parametric
performance of the ADA4938. Exceeding a junction temperature of
150°C for an extended period can result in changes in the silicon
devices, potentially causing failure.
Unit
) on
J
The power dissipated in the package (P
quiescent power dissipation and the power dissipated in the
package due to the load drive. The quiescent power is the voltage
between the supply pins (V
) times the quiescent current (IS).
S
The power dissipated due to the load drive depends upon the
particular application. The power due to load drive is calculated
by multiplying the load current by the associated voltage drop
across the device. RMS voltages and currents must be used in
these calculations.
Airflow increases heat dissipation, which effectively reducing
. In addition, more metal directly in contact with the package
θ
JA
leads/exposed pad from metal traces, through-holes, ground,
and power planes reduces the θ
JA
Figure 4 shows the maximum safe power dissipation in the
ackage vs. the ambient temperature for the 16-lead LFCSP
p
(95°C/W) and the 24-lead LFCSP (65°C/W) on a JEDEC standard
4-layer board.
3.5
3.0
2.5
ADA4938-2
2.0
1.5
1.0
MAXIMUM POWER DISSIPATION (W)
0.5
0
–40 –30 –20 –10 0 10 20 30 40 50 60 70 80 90
Figure 4. Maximum Power Dissipation vs. Temperature for a 4-Layer Board
ADA4938-1
AMBIENT TEMPERATURE (°C)
ESD CAUTION
) is the sum of the
D
.
06592-103
Rev. 0 | Page 7 of 28
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
–OUT1
–VS1–VS1–FB1
+IN1
S
S
S
S
–V
–V
–V
–V
14
13
15
16
PIN 1
1–FB
2+IN
ADA4938-1
3–IN
(Not to Scal e)
4+FB
INDICATOR
TOP VIEW
5
6
S
S
+V
+V
12 PD
11 –OUT
10 +OUT
9V
OCM
8
7
S
S
+V
+V
Figure 5. ADA4938-1 Pin Configuration
06592-003
1
–IN1
2
+FB1
3
+V
+V
–FB2
+IN2
S1
S1
ADA4938-2
4
5
6
(Not to S cale)
Figure 6. ADA4938-2 Pin Configuration
24
23
22
PIN 1
INDICATO R
TOP VIEW
9
7
8
S2
–IN2
+V
+FB2
PD1
19
20
21
18
+OUT1
V
17
OCM1
16
–V
S2
–V
15
S2
14
PD2
–OUT2
13
10
12
11
S2
+V
OCM2
V
+OUT2
06592-206
Table 7. ADA4938-1 Pin Function Descriptions
Pin No. Mnemonic Description
1 −FB Negative Output Feedback Pin.
2 +IN Positive Input Summing Node.
3 −IN Negative Input Summing Node.
4 +FB Positive Output Feedback Pin.
5 to 8 +V
9 V
S
OCM
Positive Supply Voltage.
Output Common-Mode Voltage.
10 +OUT Positive Output for Load Connection.
11 −OUT Negative Output for Load Connection.
12
PD
13 to 16 −V
S
Power-Down Pin.
Negative Supply Voltage.
Table 8. ADA4938-2 Pin Function Descriptions
Pin No. Mnemonic Description
1 −IN1 Negative Input Summing Node 1.
2 +FB1 Positive Output Feedback Pin 1.
3, 4 +V
S1
5 −FB2
6 +IN2
7 −IN2
8 +FB2
9, 10 +V
11 V
S2
OCM2
12 +OUT2
13 −OUT2
14
15, 16
17
PD2
−V
V
OCM1
S2
18 +OUT1
19 −OUT1
20
21, 22 −V
PD1
S1
23 −FB1
Positive Supply Voltage 1.
Negative Output Feedback Pin 2.
Positive Input Summing Node 2.
Negative Input Summing Node 2.
Positive Output Feedback Pin 2.
Positive Supply Voltage 2.
Output Common-Mode Voltage 2.
Positive Output 2.
Negative Output 2.
Power-Down Pin 2.
Negative Supply Voltage 2.
Output Common-Mode Voltage 1.
Positive Output 1.
Negative Output 1.
Power-Down Pin 1.
Negative Supply Voltage 1.
Negative Output Feedback Pin 1.
24 +IN1 Positive Input Summing Node 1.
Rev. 0 | Page 8 of 28
ADA4938-1/ADA4938-2
www.BDTIC.com/ADI
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, +VS = 5 V, −VS = −5 V, V
All measurements were performed with single-ended input and differential output, unless otherwise noted. For gains other than G = +1,
values for R
and RG are shown in Ta ble 11.
F
3
= 0 V, RT = 61.9 , RG = RF = 200 , G = +1, R
OCM
= 1 kΩ, unless otherwise noted.
L, dm
3
0
–3
–6
NORMALIZE D GAIN (dB)
–9
–12
G = +1
G = +2
G = +3.16
G = +5
1 10 100 1000
FREQUENCY (MHz)
Figure 7. Small Signal Frequency Response for Various Gains, V
3
0
–3
GAIN (dB)
–6
–9
VS = +5V
–12
Figu re 8. Small Signal Response for Various Supplies, V
VS = ±5V
1 10 100 1000
FREQUENCY (MHz)
OUT
3
= 0.1 V p-p
OUT
= 0.1 V p-p
0
–3
–6
NORMALIZE D GAIN (dB)
–9
–12
06592-105
G = +1
G = +2
G = +3.16
G = +5
1 10 100 1000
FREQUENCY (MHz)
06592-108
Figure 10. Large Signal Frequency Response for Various Gains
3
0
–3
GAIN (dB)
–6
–9
VS = +5V
–12
06592-106
VS = ±5V
1 10 100 1000
FREQUENCY (MHz)
06592-109
Figure 11. Large Signal Response for Various Supplies
3
0
–3
–6
NORMALIZE D GAIN (dB)
–9
–12
–40°C
+25°C
+85°C
1 10 100 1000
Figure 9. Small Signal Fr
Various Temperatures, V
FREQUENCY (MHz)
equency Response for
= 0.1 V p-p
OUT
06592-107
Rev. 0 | Page 9 of 28
0
–3
–6
NORMALIZE D GAIN (dB)
–9
–12
–40°C
+25°C
+85°C
1 10 100 1000
FREQUENCY (MHz)
Figure 12. Large Signal Frequency Response for Various Temperatures
06592-110
Loading...