Brooks Kushman P.C.
Adaptive spur cancellation techniques and multi-phase injection locked TDC for digital phase locked loop circuit
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.
University of Southern California
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Cheng-Ru Shuo-Wei
Ho Chen