Digital phase locked loop circuits with multiple digital feedback loops

Abstract

Designs of devices having digital phase locked loop (DPLL) circuits that include multiple digital feedback loops to generate high frequency clock signals by a digitally controlled oscillator (DCO). A time-to-digital converter (TDC) module is provided in such a DPLL circuit to receive an input reference clock signal and a first feedback clock signal from a first digital feedback loop and produces a digital TDC output indicative of a first phase error caused by a difference in time between the input reference clock signal and the first feedback clock signal. A second digital feedback loop is provided to generate a second digital feedback signal indicative of a second phase error caused by a difference in frequency between a desired clock signal and a generated clock signal generated by the DCO. The first and second digital feedback loops are coupled to the DCO to generate the high frequency clock signals.