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

A method for inserting delay into a start signal of a metastable ring oscillator chain-based time-to-digital circuit (TDC), comprising:

• receiving a delay selection signal indicating a determination of an amount of delay to incorporate into the start signal;
• activating one or more delay modules based on the delay selection signal, the one or more delay modules selected from a plurality of carry elements connected as a chain;
• generating delay by routing a delay signal through an activated one of the one or more delay modules;
• and
• transmitting the delay signal to a signal generating circuit configured to generate the start signal to incorporate the delay signal.

A method of calibrating a metastable ring oscillator chain-based time-to-digital circuit (TDC), comprising:

• receiving a delay selection signal indicating a determination of an amount of delay to incorporate into the start signal;
• activating one or more delay modules based on the delay selection signal, the one or more delay modules selected from a plurality of carry elements connected as a chain;
• generating delay by routing a delay signal through an activated one of the one or more delay modules;
• transmitting the delay signal to a signal generating circuit of the TDC which is configured to generate the start signal to incorporate the delay signal;
• measuring performance of the TDC using the delay selection signal to obtain an evaluation value for the delay selection signal;
• repeating the receiving, activating, generating, transmitting, and measuring step for each possible delay selection signal to obtain a corresponding evaluation value for each possible delay selection signal;
• and
• determining which of the possible delay selection signals results in a highest evaluation value.