Low Distortion
Differential ADC Driver
AD8138
FEATURES
PIN CONFIGURATION
Easy to use, single-ended-to-differential conversion
Adjustable output common-mode voltage
Externally adjustable gain
–IN
1
2
3
4
8
7
6
5
+IN
NC
V
OCM
V+
V–
+OUT
–OUT
Low harmonic distortion
AD8138
−94 dBc SFDR @ 5 MHz
NC = NO CONNECT
−85 dBc SFDR @ 20 MHz
Figure 1.
−3 dB bandwidth of 320 MHz, G = +1
Fast settling to 0.01% of 16 ns
Slew rate 1150 V/μs
TYPICAL APPLICATION CIRCUIT
5V
5V
499Ω
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
499Ω
AVDD
DVDD
V
+
IN
AIN
AIN
V
OCM
DIGITAL
OUTPUTS
ADC
AD8138
499Ω
–
V
AVSS
REF
499Ω
0.1 dB gain flatness to 40 MHz
Available in 8-Lead SOIC and MSOP packages
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 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 VOCM 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’s differential output helps balance the input to
differential ADCs, maximizing the performance of the ADC.
The AD8138 is available in both SOIC and MSOP packages for
operation over −40°C to +85°C temperatures.
Rev. F
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