Low-power CMOS variable gain amplifier based on a novel tunable transconductor

A CMOS variable gain amplifier (VGA) based on a novel linear and tunable triode transconductor is presented. The proposed transconductor employs local negative feedback for linearisation controlling the drain voltage of the input transistors biased in the triode region. The new design is able to operate at low supply voltage and the stability is guaranteed. The transconductor features a 47.75 dB dc gain and a 4.23 MHz unity gain frequency with a power consumption of only 91 mu A. To show the feasibility of the proposed transconductor, a VGA has been fabricated. Measurement results for a 0.13 mu m CMOS design show a -3 dB bandwidth above 2.8 MHz and a third-order harmonic distortion at 500 kHz below -46 dB over the whole gain range. The VGA exhibits a maximum power consumption of only 395 mu W from a single 1.2 V supply.