A low power 48-dB/stage linear-in-dB variable gain amplifier for direct-conversion receivers

In this paper, a low power Variable Gain Amplifier (VGA) circuit with an approximation to exponential gain characteristic is presented. It is achieved using current mirrors to generate appropriate current signals to bias the input stage of the VGA circuit working in triode region, and the output stage working in saturation region, respectively. The VGA circuit presented herein comes with a 549 μW maximum power consumption given a 1.8 V supply. Most important of all, it has a linear-in-dB 48-dB dynamic gain range per stage. The effect of the input trasconductance and the output resistance on the linearity of gain control is also discussed. This circuit is fabricated using a 0.18 μm standard CMOS process with a core area of 0.0045 mm².