Apparatus for programmable metastable ring oscillator period for multiple-hit delay-chain based time-to-digital circuits

Abstract

An apparatus and method for inserting delay into a start signal of a metastable ring oscillator chain-based time-to-digital circuit (TDC). Included therein is a signal generating circuit that generates 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, 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. The delay chain circuit generates an amount of delay based on a delay selection signal that is received at the enable inputs and that selects the amount of delay. The delay chain circuit additionally provides the selected amount of delay to the signal generating circuit, which incorporates the delay into the start signal.