Open-loop all-digital delay line with on-chip calibration via self-equalizing delays

Abstract

A novel calibration technique and its all-digital implementation for the open-loop delay line is presented. Fully autonomous approach iteratively compares each digitally-controlled delay stage of the line with an on-chip reference delay, correspondingly tuning selected stage and memorizing associated settings. After correcting all individual stages, the total delay of the line is compared with the external period and reference delay is then readjusted. When on-board settling monitor observes repetition of reference delay settings, it locks delay line by applying previously collected settings. The delay line is shown to lock in presence of 30% static offset of delays from their designed values. Furthermore, random spread of delays worsened by 3 times (5% PP to 15% PP ) results in only 2% decline (3% PP to 5% PP ) after applying the proposed calibration to 16-delays line.