Analog Devices' 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. 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.
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.