Low-voltage compact CMOS variable gain amplifier

A compact low-power low-voltage CMOS variable gain amplifier (VGA) is proposed. The proposed circuit merges a source-degenerated transconductance amplifier with a current-mode transimpedance amplifier, which renders voltage gain control with constant bandwidth. Coarse gain tuning is achieved by using a switched-resistor network, while fine gain tuning is obtained by using a voltage-controlled active resistor. A two-stage VGA was fabricated in a 0.35μm CMOS technology. Experimental results show that the prototype VGA has a gain range of 40 dB with more than 10 MHz bandwidth, while draining only 600μA from a 1.5 V supply voltage.