A two-phase oscillation scheme with direct background correction for VCO-based ADC

Abstract

This paper presents a two-phase oscillation scheme for ring voltage-controlled oscillator (VCO) based ADC to directly correct the deviation of the actual V-to-F transfer characteristic, including nonlinearity and the deviation of the tuning gain and center frequency. The proposed scheme facilitates correction of these non-idealities by injecting opposing signals during two phases while preserving output phase continuity, operating in the background without the need for replicas, dithering, or stringent input restrictions. Designed and simulated in 40 nm CMOS process, the variation of the tuning gain and center frequency of the ring VCO across different process, voltage, temperature (PVT) corners are within ±17 % and ±16 %, respectively, which results in gain error and offset problems in the ADC. By applying the proposed correction techniques, both these two errors can be corrected within ±1 %. Moreover, the maximum distortion can be reduced by 35.06 dB, and the signal-to-noise-and-distortion ratio (SNDR) can be improved from 50.39 dB to 75.37 dB.