ADAPTIVE SPUR CANCELLATION TECHNIQUES AND MULTI-PHASE INJECTION LOCKED TDC FOR DIGITAL PHASE LOCKED LOOP CIRCUIT

摘要

A digital phase-locked loop includes a digital loop filter, a digitally controllable oscillator (DCO), and an injection-locked calibration-free time-to-digital converter (TDC) having a ring oscillator connected to the DCO via an input buffer that converts a sinusoidal DCO signal to a differential square wave signal provided to the ring oscillator such that ring oscillator frequency matches DCO frequency. A spur cancellation loop between the TDC and digital loop filter generates a spur cancellation signal based on an estimate of a spurious tone amplitude and phase. The spur cancellation signal is subtracted from TDC output signals prior to input to the digital loop filter. The spur cancellation loop may include a gradient descent strategy, or a feedforward strategy having a high-pass filter, integer delay chain, adaptive fractional delay, and signal averaging logic to cancel multiple internal and external spurs having frequencies that are not related to the reference clock frequency.