A 40-GHz 4-Bit Digitally Controlled VGA With Low Phase Variation Using 65-nm CMOS Process

A 40-GHz variable gain amplifier (VGA) with 4-bit digital gain control and low phase variation is designed and fabricated on the 65-nm CMOS process. The digital gain control mechanism is achieved using the presented digital version current steering topology. The measured gain of the VGA is between 22 and 6 dB at 40 GHz with 16 different linear-in-decibel gain states. Using the proposed two-stage digital version current steering VGA phase compensation technique, the measured phase variation is 3.18° within a 16-dB gain control range (GCR) and the root mean square (rms) phase error is 0.89° at 40 GHz.