Method and apparatus for a phase/frequency locked loop

Abstract

A phase/frequency detector module allows operation as either a phase locked loop or a frequency locked loop. As a phased locked loop (PLL), the phase detector module is configured to decode phase differences between a reference signal and a voltage controlled oscillator (VCO) signal into phase correction signals that are updated at the rate of the VCO signal. An accumulation of the phase correction signals is implemented to form an accumulated phase error signal, which is then sampled at a lower rate than the VCO signal to accommodate slower components of the PLL, such as a digital to analog converter (DAC). As a frequency locked loop (FLL), the phase detector module is configured with frequency counters, so that frequency error may instead be detected. Any reduction of gain caused by the frequency counters is inherently equalized by the phase detector module.