A PVT Compensated Ring VCO with FVC-Assisted Digital Background Calibration

Abstract

This paper presents a ring voltage-controlled oscillator (VCO) with a novel digital background calibration for process, voltage and temperature (PVT) compensation. The ring VCO is implemented by 7-stage delay cells which consists of two cross-coupling inverters. To mitigate performance degradation due to PVT variation, the ring VCO is controlled by two 8-bit tuning codes. The calibration employs replica- VCO and frequency-to-voltage converters (FVC) to track the variation of tuning curve, and generates tuning codes to compensate for the variation. The ring VCO with the proposed calibration are designed in 40 nm CMOS with a supply voltage of 1.1 V, and the effectiveness of the calibration method is verified by the simulations of tuning curve across different PVT corners. Without calibration, the Kvco variation is ±42% and fc variation is ±58%. After calibration, the Kvco and fc variations are reduced to ±2.3% and ±2.6% respectively.