An on-die all-digital delay measurement circuit with 250fs accuracy

This paper demonstrates an in-situ delay measurement circuit which precisely characterizes key clocking circuits such as full phase rotation interpolators. This on-die all-digital circuit produces a digital output value proportional to the relative delay between two clocks, normalized to the clock period. This circuit requires no calibration for variation or process, voltage, temperature (PVT) and measures the delay with 250fs absolute accuracy and repeatability of 10fs-rms.