Digitally programmable decibel-linear CMOS VGA for low-power mixed-signal applications

A new technique for realizing CMOS digitally-controlled decibel-linear variable gain amplifier (VGA) circuits is described. CMOS VGA circuits employing the proposed technique are then given. Besides being effective and simple to use from a system point of view, the VGA circuits offer a stable gain characteristic with precise gain control that is achievable without component spreading. The VGA provides a 25 dB gain control range per stage, with 0.55 dB gain steps and a gain error of less than 0.5 dB. It can also be digitally reconfigured to give a 60 dB gain control range with 6 dB gain steps. The VGA circuit provides digital offset trimming, processes voltage or current input signals and operates in a fully differential configuration. Simulation and experimental results are provided.