Described is an apparatus which comprises: a time-to-digital converter (TDC) to receive a reference clock and a feedback clock, wherein the TDC is to generate a digital output code representing a time difference between the reference clock and the feedback clock; a circuitry to apply a digital code to an output of the TDC; and a node to receive the digital output code from the TDC and the digital code from the circuitry, wherein the circuitry is to monitor the digital output code and to control the TDC according to at least the monitored digital output code.