150MHz BW with linear in dB gain control variable gain amplifier

The VCA820 is a dc-coupled, wideband, linear in dB, continuously variable, voltage-controlled gain amplifier. The VCA820 provides a differential input to single-ended conversion with a high-impedance gain control input, used to vary the gain down 40 dB from the nominal maximum gain set by the gain resistor (RG) and feedback resistor (RF).

The VCA820 internal architecture consists of two input buffers and an output current feedback amplifier stage, integrated with a multiplier core to provide a complete variable gain amplifier (VGA) system that does not require external buffering. The maximum gain is set externally with two resistors, providing flexibility in designs. The maximum gain is intended to be set between +2 V/V and +100 V/V. Operating from ±5-V supplies, the gain control voltage for the VCA820 adjusts the gain linearly in dB as the control voltage varies from 0 V to +2 V. For example, set for a maximum gain of +10 V/V, the VCA820 provides 20 dB, at +2-V input, to –20 dB at 0-V input of gain control range. The VCA820 offers excellent gain linearity. For a 20-dB maximum gain, and a gain-control input voltage varying between 1 V and 2 V, the gain does not deviate by more than ±0.4dB (maximum at +25°C).