Patent ID: 8786474

Claim:
An apparatus for inserting delay into a start signal of a metastable ring oscillator chain-based time-to-digital circuit (TDC), comprising: a signal generating circuit configured to generate the start signal; a plurality of carry elements connected as a chain, each of the carry elements having an input to receive a stop signal; and a delay chain circuit including one or more delay modules selected from the plurality of carry elements, at least one feedback line connected between at least one of the delay modules and the signal generating circuit, and a plurality of enable inputs each provided in a respective one of the delay modules, wherein the delay chain circuit is configured to generate an amount of delay based on a delay selection signal that is received at the enable inputs and that selects the amount of delay, and is configured to provide the selected amount of delay to the signal generating circuit, which is further configured to incorporate the delay into the start signal.