The AD8338 is a variable gain amplifier (VGA) for applicationsthat require a fully differential signal path, low power, low noise,and a well-defined gain over frequency. Although the inputs aredifferential, the device can also be driven with a single-endedsource if required.The basic gain function is linear-in-dB and is controlled by thevoltage applied to Pin GAIN. The nominal gain range spansfrom 0 dB to 80 dB for control voltages between 0.1 V to 1.1 Vwith a slope of 12.5 mV/dB. The nominal gain range can beshifted up or down via direct access to Pin INPD and Pin INMD,the current inputs of the VGA. For example, driving the INPDand INMD pins with 50 Ω resistors shifts the gain range up by20 dB, that is, 20 dB to 100 dB, and lowers the input referrednoise of the device to 1.5 nV/√Hz. Additionally, the gain slopecan be inverted via logic Pin MODE.The AD8338 includes additional circuit blocks to enable inputoffset correction and automatic gain control (AGC). DC offsetvoltages are removed by the offset correction circuit, whichbehaves like a high-pass filter whose corner is set with an externalcapacitor. The AGC function varies the gain of the AD8338 tomaintain a constant rms output voltage. An externally appliedvoltage to Pin VAGC with respect to the voltage at Pin VREFsets the output rms amplitude. A capacitor from Pin DETO toground sets the response time of the AGC circuit.The AD8338 offers additional versatility by providing access tothe internal summing nodes of the VGA core and the outputamplifiers. With the addition of a few external passive components,users can customize the gain, bandwidth, input impedance, andnoise profile of the device to fit their application.The AD8338 uses a single-supply voltage of 3.0 V to 5.0 V andis very power efficient, consuming as little as 3 mA quiescentcurrent at mid gain. The AD8338 is available in a 3 mm × 3 mm,RoHS-compliant, 16-lead LFCSP and is specified over theindustrial temperature range of −40°C to +85°C.APPLICATIONS Front end for inductive telemetry systems Ultrasonic signal receivers Signal compression for driving an ADC AGC amplifiers

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