REV. A
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.
a
AD8138
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703 © Analog Devices, Inc., 1999
Low Distortion
Differential ADC Driver
FUNCTIONAL BLOCK DIAGRAM
1
2
3
4
8
7
6
5
AD8138
NCV
OCM
–OUT
V+
NC = NO CONNECT
+IN
V–
–IN
+OUT
FEATURES
Easy to Use Single-Ended-to-Differential Conversion
Adjustable Output Common-Mode Voltage
Externally Adjustable Gain
Low Harmonic Distortion
–94 dBc—Second, <–114 dBc—Third @ 5 MHz into
800 V Load
–87 dBc—Second, –85 dBc—Third @ 20 MHz into
800 V Load
–3 dB Bandwidth of 320 MHz, G = +1
Fast Settling to 0.01% of 16 ns
Slew Rate 1150 V/ms
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 65 V
Low Power 90 mW on +5 V
0.1 dB Gain Flatness to 40 MHz
Available in 8-Lead SOIC
APPLICATIONS
ADC Driver
Single-Ended-to-Differential Converter
IF and Baseband Gain Block
Differential Buffer
Line Driver
PRODUCT DESCRIPTION
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 ampli-
fier. 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 output gain and phase matching
that are balanced, suppressing even order harmonics. The inter-
nal feedback 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- 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 per-
formance make it well suited for a wide variety of signal pro-
cessing and data acquisition applications.
The AD8138 is offered in an 8-lead SOIC that operates over
the industrial temperature range of –40 C to +85 C.
TYPICAL APPLICATION CIRCUIT
AIN
AIN
AVDD DVDD
AVSS
V
REF
ADC
499V
499V
499V
499V
V
IN
V
OCM
+5V
+5V
DIGITAL
OUTPUTS
AD8138
+
–