A 2.35GHz CMOS LC-VCO with high linearity of frequency tuning by using PMOS varactors in AI chip

Mos varactors in standard CMOS technology usually show highly nonlinear C-V characteristics, which results in nonlinear frequency tuning in VCO's directly[3]. In this work, we present a new varactor configuration to improve the C-V performance. The new varactor configuration is composed of three pairs of PMOS accumulation varactors connected in parallel and two voltage level shifters1. With this new varactor configuration, a 2.35GHz CMOS LC-VCO is designed in 0.35μm CMOS technology. Simulation results show that the VCO has high linearity of frequency tuning when control voltage VC changes from 0V to 3.3V. At the power supply voltage of 3.3V, the VCO consumes 3.4mA current, phase noise is -123dBc/Hz at 1MHz offset from the carrier frequency, and the frequency tuning range is 33. 25%.