Pll using a dco period length feedback clock pulse to determine phase error and tdc gain

Abstract

A phase-locked loop (PLL) includes a digitally controlled oscillator (DCO) that generates a DCO output signal. A feedback divider is coupled to the DCO output signal, divides the DCO output signal, and generates a feedback clock signal. The feedback clock signal is generated as a pulse having a pulse width equal to one period of the DCO output signal. A time-to-digital converter (TDC) receives a reference clock signal and the feedback clock signal and generates a TDC output that indicates a phase difference between the reference clock signal and the feedback clock signal. The TDC output also provides gain information indicating how many delay elements correspond to the period of the DCO output signal. The gain information can be used to more accurately cancel quantization error in the PLL.