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Low Distortion
Differential ADC Driver
AD8138
FEATURES
Easy to use, single-ended-to-differential conversion
Adjustable output common-mode voltage
Externally adjustable gain
Low harmonic distortion
−94 dBc SFDR @ 5 MHz
−85 dBc SFDR @ 20 MHz
−3 dB bandwidth of 320 MHz, G = +1
Fast settling to 0.01% of 16 ns
Slew rate 1150 V/μs
Fast overdrive recovery of 4 ns
Low input voltage noise of 5 nV/√Hz
1 mV typical offset voltage
Wide supply range +3 V to ±5 V
Low power 90 mW on 5 V
0.1 dB gain flatness to 40 MHz
Available in 8-Lead SOIC and MSOP packages
PIN CONFIGURATION
–IN
1
V
OCM 2
V+
3
+OUT
4
8
7
6
+IN
NC
V–
01073-001
AD8138
Figure 1.
5
–OUT
NC = NO CONNECT
TYPICAL APPLICATION CIRCUIT
5V
499Ω
V
IN
499Ω
V
OCM
499Ω
+
AIN
AIN
499Ω
AVDD
DVDD
DIGITAL
OUTPUTS
V
REF
01073-002
5V
AD8138
–
ADC
AVSS
Figure 2.
APPLICATIONS
ADC drivers
Single-ended-to-differential converters
IF and baseband gain blocks
Differential buffers
Line drivers
GENERAL DESCRIPTION
The AD8138 is a major advancement over op amps for
differential signal processing. The AD8138 can be used as a
single-ended-to-differential amplifier or as a differential-to-
differential amplifier. The AD8138 is as easy to use as an op
amp and greatly simplifies differential signal amplification and
driving. Manufactured on ADI’s proprietary XFCB bipolar
process, the AD8138 has a −3 dB bandwidth of 320 MHz and
delivers a differential signal with the lowest harmonic distortion
available in a differential amplifier. The AD8138 has a unique
internal feedback feature that provides balanced output gain
and phase matching, suppressing even order harmonics. The
internal feed-back circuit also minimizes any gain error that
would be associated with the mismatches in the external gain
setting resistors.
The AD8138’s differential output helps balance the input to
differential ADCs, maximizing the performance of the ADC.
The AD8138 eliminates the need for a transformer with high
performance ADCs, preserving the low frequency and dc infor-
mation. The common-mode level of the differential output is
adjustable by a voltage on the V
OCM
pin, easily level-shifting the
input signals for driving single-supply ADCs. Fast overload
recovery preserves sampling accuracy.
The AD8138 distortion performance makes it an ideal ADC
driver for communication systems, with distortion performance
good enough to drive state-of-the-art 10-bit to 16-bit converters
at high frequencies. The AD8138’s high bandwidth and IP3 also
make it appropriate for use as a gain block in IF and baseband
signal chains. The AD8138 offset and dynamic performance
makes it well suited for a wide variety of signal processing and
data acquisition applications.
The AD8138 is available in both SOIC and MSOP packages for
operation over −40°C to +85°C temperatures.
Rev. F
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.
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
©2006 Analog Devices, Inc. All rights reserved.
AD8138
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications....................................................................................... 1
Pin Configuration............................................................................. 1
Typical Application Circuit ............................................................. 1
General Description ......................................................................... 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
±D
IN
to ±OUT Specifications...................................................... 3
V
OCM
to ±OUT Specifications ..................................................... 4
±D
IN
to ±OUT Specifications...................................................... 5
V
OCM
to ±OUT Specifications ..................................................... 6
Absolute Maximum Ratings............................................................ 7
Thermal Resistance ...................................................................... 7
ESD Caution.................................................................................. 7
Pin Configuration and Function Descriptions............................. 8
Typical Performance Characteristics ............................................. 9
Test Circuits..................................................................................... 15
Operational Description................................................................ 16
Definition of Terms.................................................................... 16
Theory of Operation ...................................................................... 17
Analyzing an Application Circuit ............................................ 17
Setting the Closed-Loop Gain .................................................. 17
Estimating the Output Noise Voltage ...................................... 17
The Impact of Mismatches in the Feedback Networks ......... 18
Calculating an Application Circuit’s Input Impedance......... 18
Input Common-Mode Voltage Range in Single-Supply
Applications ................................................................................ 18
Setting the Output Common-Mode Voltage .......................... 18
Driving a Capacitive Load......................................................... 18
Layout, Grounding, and Bypassing.............................................. 19
Balanced Transformer Driver ....................................................... 20
High Performance ADC Driving ................................................. 21
3 V Operation ................................................................................. 22
Outline Dimensions ....................................................................... 23
Ordering Guide .......................................................................... 23
REVISION HISTORY
1/06—Rev. E to Rev. F
Changes to Features.......................................................................... 1
Added Thermal Resistance Section and Maximum Power
Dissipation Section........................................................................... 7
Changes to Balanced Transformer Driver Section..................... 20
Changes to Ordering Guide .......................................................... 23
3/03—Rev. D to Rev. E
Changes to Specifications ................................................................ 2
Changes to Ordering Guide ............................................................ 4
Changes to TPC 16........................................................................... 6
Changes to Table I ............................................................................ 9
Added New Paragraph after Table I ............................................. 10
Updated Outline Dimensions ....................................................... 14
7/02—Rev. C to Rev. D
Addition of TPC 35 and TPC 36 .....................................................8
6/01—Rev. B to Rev. C
Edits to Specifications ......................................................................2
Edits to Ordering Guide ...................................................................4
12/00—Rev. A to Rev. B
9/99—Rev. 0 to Rev. A
3/99—Rev. 0: Initial Version
Rev. F | Page 2 of 24
AD8138
SPECIFICATIONS
±D
IN
to ±OUT SPECIFICATIONS
At 25°C, V
S
= ±5 V, V
OCM
= 0, G = +1, R
L, dm
= 500 Ω, unless otherwise noted. Refer to Figure 39 for test setup and label descriptions. All
specifications refer to single-ended input and differential outputs, unless otherwise noted.
Table 1.
Parameter
DYNAMIC PERFORMANCE
−3 dB Small Signal Bandwidth
Bandwidth for 0.1 dB Flatness
Large Signal Bandwidth
Slew Rate
Settling Time
Overdrive Recovery Time
NOISE/HARMONIC PERFORMANCE
1
Second Harmonic
Conditions
V
OUT
= 0.5 V p-p, C
F
= 0 pF
V
OUT
= 0.5 V p-p, C
F
= 1 pF
V
OUT
= 0.5 V p-p, C
F
= 0 pF
V
OUT
= 2 V p-p, C
F
= 0 pF
V
OUT
= 2 V p-p, C
F
= 0 pF
0.01%, V
OUT
= 2 V p-p, C
F
= 1 pF
V
IN
= 5 V to 0 V step, G = +2
V
OUT
= 2 V p-p, 5 MHz, R
L, dm
= 800 Ω
V
OUT
= 2 V p-p, 20 MHz, R
L, dm
= 800 Ω
V
OUT
= 2 V p-p, 70 MHz, R
L, dm
= 800 Ω
V
OUT
= 2 V p-p, 5 MHz, R
L, dm
= 800 Ω
V
OUT
= 2 V p-p, 20 MHz, R
L, dm
= 800 Ω
V
OUT
= 2 V p-p, 70 MHz, R
L, dm
= 800 Ω
20 MHz
20 MHz
f = 100 kHz to 40 MHz
f = 100 kHz to 40 MHz
V
OS, dm
= V
OUT, dm
/2; V
DIN+
= V
DIN−
= V
OCM
= 0 V
T
MIN
to T
MAX
variation
T
MIN
to T
MAX
variation
Differential
Common mode
−2.5
Min
290
Typ
320
225
30
265
1150
16
4
−94
−87
−62
−114
−85
−57
−77
37
5
2
±1
±4
3.5
−0.01
6
3
1
−4.7 to +3.4
−77
7.75
95
−66
+2.5
7
Max
Unit
MHz
MHz
MHz
MHz
V/μs
ns
ns
dBc
dBc
dBc
dBc
dBc
dBc
dBc
dBm
nV/√Hz
pA/√Hz
mV
μV/°C
μA
μA/°C
MΩ
MΩ
pF
V
dB
V p-p
mA
dB
Third Harmonic
IMD
IP3
Voltage Noise (RTI)
Input Current Noise
INPUT CHARACTERISTICS
Offset Voltage
Input Bias Current
Input Resistance
Input Capacitance
Input Common-Mode Voltage
CMRR
OUTPUT CHARACTERISTICS
Output Voltage Swing
Output Current
Output Balance Error
1
∆V
OUT, dm
/∆V
IN, cm
; ∆V
IN, cm
= ±1 V
Maximum ∆V
OUT
; single-ended output
∆V
OUT, cm
/∆V
OUT, dm
; ∆V
OUT, dm
= 1 V
−70
Harmonic distortion performance is equal or slightly worse with higher values of R
L, dm
. See Figure 17 and Figure 18 for more information.
Rev. F | Page 3 of 24
AD8138
V
OCM
to ±OUT SPECIFICATIONS
At 25°C, V
S
= ±5 V, V
OCM
= 0, G = +1, R
L, dm
= 500 Ω, unless otherwise noted. Refer to Figure 39 for test setup and label descriptions. All
specifications refer to single-ended input and differential outputs, unless otherwise noted.
Table 2.
Parameter
DYNAMIC PERFORMANCE
−3 dB Bandwidth
Slew Rate
INPUT VOLTAGE NOISE (RTI)
DC PERFORMANCE
Input Voltage Range
Input Resistance
Input Offset Voltage
Input Bias Current
V
OCM
CMRR
Gain
POWER SUPPLY
Operating Range
Quiescent Current
Power Supply Rejection Ratio
OPERATING TEMPERATURE RANGE
Conditions
Min
Typ
250
330
17
±3.8
200
±1
0.5
−75
1
Max
Unit
MHz
V/μs
nV/√Hz
V
kΩ
mV
μA
dB
V/V
V
mA
μA/°C
dB
°C
f = 0.1 MHz to 100 MHz
V
OS, cm
= V
OUT, cm
; V
DIN+
= V
DIN–
= V
OCM
= 0 V
∆V
OUT, dm
/∆V
OCM
; ∆V
OCM
= ±1 V
∆V
OUT, cm
/∆V
OCM
; ∆V
OCM
= ±1 V
–3.5
+3.5
0.9955
±1.4
18
1.0045
±5.5
23
−70
+85
T
MIN
to T
MAX
variation
∆V
OUT, dm
/∆V
S
; ∆V
S
= ±1 V
−40
20
40
−90
Rev. F | Page 4 of 24
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