A CMOS wideband highly linear variable gain amplifier

This work presents the design of a wideband highly linear variable gain amplifier (VGA). The proposed VGA consists of 3 stage digitally gain controlled amplifiers and a fixed gain amplifier. The circuit topologies of the amplifiers are pseudo differential inverter, which allows maximum headroom voltage swing. As a result, highly linear operation is achieved. A simple digitally gain controlled method is proposed, that provides 15 dB control range, with 3 control bits. Furthermore, with the proposed gain control method, linearity and gain bandwidth is maintained in low gain mode operation. The proposed VGA is implemented in a 65 nm CMOS technology. The measured VGA shows more than 1.2 GHz 3 dB gain bandwidth, 15 dB control gain range. The measured VGA consumes 7.5 mA from 1.2 V power supply.