A Ka-Band 6-Bit Digital-Controlled Differential VGA With 16-dB Gain Control Range and 4.9° Phase Variation in 65-nm CMOS

A Ka-band differential variable gain amplifier (VGA) applying symmetrical unit arrays with 6-bit digital-controlled is presented. The proposed VGA, based on the conventional current steering theory, uses symmetrical unit arrays that keep the output impedance constant, while digital-controlled voltage changes. Then it combines neutralizing capacitances to counteract the Miller effect of parasitic capacitances between gain and drain of input transistors. The VGA with symmetrical unit arrays ensures the consistency of phase variation during gain fluctuation. The VGA is fabricated in a 65-nm CMOS technology, and achieves −20.2 to −4.2 dB gain varied with 1.52 dBm IP1dB as well as 8.6 dB noise figure at 36 GHz and less than 4.9° phase variation, while consuming 15.6 mW across 30.5–39 GHz frequency range.