AD8338 Datasheet, PDF (1/16 Pages) Analog Devices – Low Power, 18 MHz Variable Gain Amplifier

Data Sheet
Low Power, 18 MHz Variable Gain Amplifier
AD8338
FEATURES
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
Automatic gain control feature
Wide gain range for high dynamic range signals
APPLICATIONS
Front end for inductive telemetry systems
Ultrasonic signal receivers
RF baseband signal conditioning
GENERAL DESCRIPTION
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.
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.
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.
INPR
INMR
INPD
INMD
FUNCTIONAL BLOCK DIAGRAM
VBAT OFSN VREF
OFFSET NULL
VGA CORE
+
–
0dB TO 80dB
GAIN INTERFACE
AD8338
+
OUTPUT
STAGE
0dB
–
VREF
AUTOMATIC
GAIN
CONTROL
FBKP
OUTP
OUTM
FBKM
COMM
100
80
60
40
20
0
MODE GAIN DETO
Figure 1.
VGAIN = 1.1V
VGAIN = 1.0V
VGAIN = 0.9V
VGAIN = 0.8V
VGAIN = 0.7V
VGAIN = 0.6V
VGAIN = 0.5V
VGAIN = 0.4V
VGAIN = 0.3V
VGAIN = 0.2V
VGAIN = 0.1V
VAGC
–20
–40
10k
100k
1M
10M
FREQUENCY (Hz)
Figure 2. Gain vs. Frequency
100M
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 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
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