A 7-bit 360° phase rotator in 45nm CMOS interpolates between coarse phases by modulating the injection point of an oscillator. This architecture decouples phase resolution from device sizing. INL and DNL are improved by independently adapting the delay of each oscillator stage. A digital phase-locked loop using a time-to-digital converter based on a tracking ADC keeps the oscillator tuned to the injection frequency. The measured DNL and INL at 4.05GHz with phase calibration are 0.4 and 1.2 LSBs, respectively, while consuming 14.3mW.
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O’Mahony et al. (2010) studied this question.