US Patent 7522690 Jitter self test

Jitter is measured by receiving a first reference signal at a first phase-locked loop (PLL) circuit and generating at an output of the first phase-locked loop circuit an output signal based at least in part on the first reference signal, the output signal including a jitter component to be measured. A signal corresponding to the output signal and a signal corresponding to the first reference signal are compared in a phase detector of a second phase-locked loop circuit. A value corresponding to an output of the comparison is stored that includes information indicative of the measured jitter component.