Real time counter-based method for the determination and measurement of frequency lock time in phase-locked loops

Abstract

A system to test a PLL circuit driven by a reference clock includes a first counter coupled to a reference clock output, a first buffer coupled to the first counter, a second counter coupled to a controlled-oscillator (CO) output of the PLL circuit, a second buffer coupled to the second counter, and a processor configured to compute a PLL lock time according to second count values in the second buffer, and to compute a PLL startup slope according to the first count values in the first buffer and the second count values in the second buffer. A method includes powering up a PLL circuit of a wafer, sampling count values of a reference clock and second count values of the PLL circuit and computing a PLL performance parameter according to the sampled count values in a buffer.