Precise delay generation using coupled oscillators

A new delay generator based on a series of coupled ring oscillators has been developed; it produces precise delays with subgate delay resolution for chip testing applications. It achieves a delay resolution equal to a buffer delay divided by the number of rings. The coupling employed forces the outputs of a linear array of ring oscillators oscillating at the same frequency to be uniformly offset in phase by a precise fraction of a buffer delay. The buffer stage used in the ring oscillators is based on a source-coupled pair and achieves high supply noise rejection while operating at low supply voltages. Experimental results from a 2-μm N-well CMOS implementation of the delay generator demonstrate that it can achieve an output delay resolution of 101 ps while operating at 141 MHz with a peak error of 58 ps