Phase-locked loops (pll), including time-to-digital converter (tdc) gain calibration circuits and related methods

Abstract

In a calibrated phase-locked loop (PLL), a time-to-digital (TDC) converter circuit can be calibrated to a nominal gain by a calibration circuit to achieve a desired jitter response in the PLL. The TDC circuit in the PLL measures a time difference between the reference clock and a feedback signal as a number of time increments, and the calibration circuit adjusts a resolution of the measurement by adjusting the length of the time increments (i.e., resolution). In a Vernier method employed to measure the time difference, the length of a time increment is determined by a delay difference between a first delay of a first delay circuit in a first series of first delay circuits and a second delay of a second delay circuit in a second series of second delay circuits. Adjusting the resolution of the TDC circuit includes adjusting the delay difference between the first delay and the second delay.