Abstract: A re-circulating time-to-digital converter (TDC) can include a triggered reference ring oscillator (TRRO) and a delay module. The triggered reference ring oscillator can, when triggered by a reference signal edge, generate a periodic ring oscillator signal with a ring oscillator period that is a selected ratio of a voltage-controlled oscillator (VCO) period. The delay module can store, in a plurality of latches, samples of a VCO signal docked by the periodic ring oscillator signal. Each latch can generate an output of the sample, and each latch output can represent a time difference polarity between VCO signal and TRRO signal. In another example, the re-circulating TDC can include the triggered reference ring oscillator, a digital frequency lock module, and a TDC post-process module. The digital frequency lock module can generate a ring oscillator control signal, which sets the ring oscillator period for the triggered reference ring oscillator.

Abstract: A re-circulating time-to-digital converter (TDC) can include a triggered reference ring oscillator (TRRO) and a delay module. The triggered reference ring oscillator can, when triggered by a reference signal edge, generate a periodic ring oscillator signal with a ring oscillator period that is a selected ratio of a voltage-controlled oscillator (VCO) period. The delay module can store, in a plurality of latches, samples of a VCO signal docked by the periodic ring oscillator signal. Each latch can generate an output of the sample, and each latch output can represent a time difference polarity between VCO signal and TRRO signal. In another example, the re-circulating TDC can include the triggered reference ring oscillator, a digital frequency lock module, and a TDC post-process module. The digital frequency lock module can generate a ring oscillator control signal, which sets the ring oscillator period for the triggered reference ring oscillator.