A 2–6.5 GHz CMOS variable gain amplifier for vector-sum phase shifters

A wideband CMOS variable gain amplifier (VGA) for application in vector-sum phase shifters is presented. The VGA exhibits a continous, linear-in-magnitude gain control curve by using a programmable transconductance multiplier. Wideband input matching is achieved by employing the common-gate configuration at the input stage. To improve the gain flatness and the output matching, a modified three-stage Cherry-Hooper amplifier with inductive peaking is proposed. Using a standard 0.13-μm CMOS process, the measured 3-dB bandwidth is from 2 to 6.5 GHz with a linear-in-magnitude gain tuning range of 14 dB, and transmission phase error less than 4°. Operating at 1.2 V, the chip consumes 6 mW and occupies 0.6 mm² including test pads.