Low-Voltage 0.81mW, 1-32 CMOS VGA with 5% Bandwidth variations and 38dB DC rejection

Abstract

A CMOS low-voltage amplifier with approximately constant bandwidth and DC rejection is introduced. The design is based on the cascade of a wide linear input range OTA, an op-amp and a servo-loop with extremely large time constants. It operates with ±0.45V supplies and a power consumption of 0.81mW in 180nm technology. The bandwidth changes only from 9.08MHz to 9.54MHz over a gain range from 1 to 32, it has a 9.8Hz low cutoff frequency and a DC attenuation of 38dBs. DC floating voltage sources are used to keep the gates of all differential pairs at a constant value close to a supply rail in order to operate the amplifier circuit with minimum supply voltage. The proposed circuit has small and large signal figures of merit FOM SS = 5380 (MHz*pF/mW) and FOM LS = 0.0085((V/ns)*pF/mA) for a nominal gain A = 32.