A 24GHz CMOS LC-VCO with tuned push-pull buffer amplifier

A low power, area-efficiency differential push-pull buffer amplifier with tuned output for mm-wave LC-VCO was presented in this paper. The push-pull technique is introduced to the differential LC-tuned buffer amplifier to increase the trans-conductor without increasing the power dissipation. Moreover, the proposed amplifier needs only one resonator tank for differential tuned outputs and such circuit topology can significantly reduce chip area. A 24GHz LC-VCO with digitally tuned varactor array for coarse tuning was also presented as part of the LO generator. Since the output frequency of the VCO is divided into several sub-curves, digitally tuned varactor array is also adopted to the tuned buffer amplifier and synchronized switched with those in LC-VCO to keep up the center frequency of the resonator tank. The designed VCO with the proposed buffer amplifier was implemented in 90nm CMOS process and occupies an area of 480um × 450um. It covers a frequency range from 23.7GHz to 25.2GHz and the measured phase noise is -116dBc/Hz@10MHz at 24GHz output.