Low Power, 18 MHz Variable Gain Amplifier
AD8338
Data Sheet
FEATURES
FUNCTIONAL BLOCK DIAGRAM
VBAT OFSN VREF
Voltage controlled gain range of 0 dB to 80 dB
3 mA supply current at gain of 40 dB
Low frequency (LF) to 18 MHz operation
Supply range: 3.0 V to 5.0 V
Adjustable gain range
Low noise: 4.5 nV/√Hz
Fully differential signal path
Offset correction (offset null) feature
Adjustable bandwidth
Internal 1.5 V reference
16-lead LFCSP
OFFSET NULL
FBKP
AD8338
VGA CORE
+
INPR
+
OUTP
OUTM
OUTPUT
STAGE
0dB
–
–
INMR
INPD
INMD
0dB TO 80dB
VREF
FBKM
AUTOMATIC
GAIN
CONTROL
GAIN INTERFACE
Automatic gain control feature
Wide gain range for high dynamic range signals
COMM
MODE GAIN
DETO
VAGC
APPLICATIONS
Figure 1.
Front end for inductive telemetry systems
Ultrasonic signal receivers
RF baseband signal conditioning
100
80
V
= 1.1V
GAIN
V
V
V
V
V
V
V
V
= 1.0V
= 0.9V
= 0.8V
= 0.7V
= 0.6V
= 0.5V
= 0.4V
= 0.3V
GAIN
GAIN
GAIN
GAIN
GAIN
GAIN
GAIN
GAIN
60
GENERAL DESCRIPTION
40
The AD8338 is a variable gain amplifier (VGA) for applications
that require a fully differential signal path, low power, low noise,
and a well-defined gain over frequencies from LF to 18 MHz. The
device can also operate using single-ended sources if required.
20
V
V
= 0.2V
= 0.1V
GAIN
GAIN
0
The basic gain function is linear-in-dB with a nominal gain range
of 0 dB to 80 dB; the nominal gain range corresponds to a control
voltage on the GAIN pin of 0.1 V to 1.1 V. The gain range can be
adjusted up or down via direct access to the internal summing
nodes at the INPD and INMD pins. For example, if a 47 Ω resistor
is applied to the INPD and INMD pins, a gain range of 20 dB to
100 dB is set with an input referred noise level of 1.5 nV√Hz.
–20
–40
10k
100k
1M
FREQUENCY (Hz)
10M
100M
Figure 2. Gain vs. Frequency
The AD8338 offers additional versatility by allowing user access
to the internal summing nodes. With a few discrete components,
users can customize the gain, bandwidth, input impedance, and
noise profile of the part to fit their application.
The AD8338 includes additional circuits to enable offset correction
and automatic gain control (AGC). DC offset voltages are removed
by the offset correction circuit, which behaves like a high-pass filter.
The high-pass filter corner frequency is set using an external
capacitor. The AGC function varies the gain of the AD8338 to
maintain a constant rms output voltage. A user supplied voltage
controls the target output rms voltage. A user supplied capacitor
to ground at the DETO pin controls the response time of the
AGC circuit.
The AD8338 uses a single supply voltage of 3.0 V to 5.0 V and is
very power efficient, consuming as little as 3 mA quiescent current.
The AD8338 is available in a 3 mm × 3 mm, RoHS compliant,
16-lead LFCSP. It is specified over the industrial temperature range
of −40°C to +85°C.
Rev. 0
Document Feedback
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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
Technical Support
©2013 Analog Devices, Inc. All rights reserved.
www.analog.com
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