A differential automatic gain control circuit with two-stage −10 to 50 dB tuning range VGAs

Abstract

A differential automatic gain control (AGC) circuit is presented. The AGC architecture contains twostage variable gain amplifiers (VGAs) which are implemented with a Gilbert cell, a peak detector (PD), a low pass filter, an operational amplifier, and two voltage to current (V -I ) convertors. One stage VGA achieves 30 dB gain due to the use of active load. The AGC circuit is implemented in UMC 0.18-m single-poly six-metal CMOS process technology. Measurement results show that the final differential output swing of the 2nd stage VGA is about 0.9-Vpp; the total gain of the two VGAs can be varied linearly from -10 to 50 dB when the control voltage varies from 0.3 to 0.9 V. The final circuit (containing output buffers and a band-gap reference) consumes 37 mA from single 1.8 V voltage supply. For a 50 mV amplitude 60% modulation depth input AM signal it needs 100 s to stabilize the output. The frequency response of the circuit has almost a constant -3 dB bandwidth of 2.2 MHz. Its OIP3 result is at 19 dBm.