Reliability analysis of MOS varactor in CMOS LC VCO

Abstract

The paper investigates the reliability of MOS varactor tuned voltage-controlled oscillators (VCO). Due to the stress induced threshold voltage shift of the MOS varactor, the resonant tank degrades and the center frequency and phase noise of VCO deviate. The behavior is modeled and an adaptive body biasing scheme is proposed to make VCO resilient to reliability. In the mean time it does not degrade the VCO performance. An LC VCO at 24GHz carrier frequency with adaptive body biasing is compared with VCO without such biasing design in PTM 65nm technology. The ADS simulation results show that the biasing design helps improve the robustness of the VCO in resonant frequency. The design reduces the frequency sensitivity of VCO by 20% when subjected to threshold voltage degradation.