A Digitally-Controlled Variable Gain Amplifier with 0.5-dB Step and Constant-Bandwidth for Passive MM-wave Imaging Receiver

This paper presents a wide bandwidth digitally-controlled variable gain amplifier (VGA) for the passive millimeter-wave (mm-wave) imaging receiver in a 40-nm CMOS. The proposed VGA consists of a three-stage VGA core and an output buffer. By introducing a variable transconductance stage and a variable transimpedance stage simultaneously, the VGA achieves high gain, wide gain range, precise gain step and constant bandwidth. The simulation results illustrate that, with a gain from 33 to 63.5 dB, a constant 3-dB bandwidth over 3.5 GHz is achieved. With the proposed gain tuning method, the gain step size error is less than ±0.15 dB. The VGA consumes only 17 mA from a 1.2 V supply and the core area is only 0.03 mm 2 .