# US 8,786,474 B1 · Apparatus for programmable metastable ring oscillator period for multiple-hit delay-chain based time-to-digital circuits

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- Number: US 8,786,474 B1
- Document ID: US8786474B1
- Status: Granted
- Kind: B1
- Application number: 13/841,364
- Filed: 2013-03-15
- Granted: 2014-07-22
- Earliest claimed: 2013-03-15
- Assignees: Kabushiki Kaisha Toshiba; Toshiba Medical Systems Corporation
- Applicants: Kabushiki Kaisha Toshiba; Toshiba Medical Systems Corporation
- Inventors: Gregory J. Mann
- Web page: https://patentgrep.com/patent/US8786474B1

## CPC

- G04F 10/005: {Time-to-digital converters [TDC] (analog-to-digital converters with intermediate conversion to time or phase H03M1/50, H03M1/60)}
- H04N 25/78: Readout circuits for addressed sensors, e.g. output amplifiers or A/D converters
- G04F: TIME-INTERVAL MEASURING (measuring pulse characteristics G01R, e.g. G01R29/02; in radar or like systems G01S)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## 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.

## Claims

### Claim 1

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.

### Claim 2 (depends on 1)

The apparatus according to claim 1, wherein the signal generating circuit is further configured to incorporate the delay into the start signal between edges in the signal.

### Claim 3 (depends on 1)

The apparatus according to claim 1, further comprising:
a time determining circuit configured to determine the time at which an event occurred based on state information transferred from each of the delay elements.

### Claim 4 (depends on 1)

The apparatus according to claim 1, wherein the delay selection signal provides an indication to each delay module whether the respective delay module is activated to generate delay.

### Claim 5 (depends on 1)

The apparatus according to claim 1, wherein the signal generating circuit includes at least one flip-flop.

### Claim 6 (depends on 1)

The apparatus according to claim 1, wherein each delay module includes at least one hardware based look up table (LUT).

### Claim 7 (depends on 1)

The apparatus according to claim 1, wherein each delay module includes at least one flip-flop.

### Claim 8 (depends on 1)

The apparatus according to claim 1, wherein the delay selection signal is determined by user input.

### Claim 9 (depends on 1)

The apparatus according to claim 1, wherein the delay selection signal is determined by an algorithm which determines the optimal propagation delay for the TDC.

### Claim 10

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.

### Claim 11 (depends on 10)

The method according to claim 10, further comprising:
receiving the delay signal at the signal generating circuit;
generating a start signal incorporating the delay signal into the start signal;
transmitting the start signal generated by the generating to the plurality of carry elements connected as a chain;
receiving a stop signal at each of the plurality of carry elements;
transmitting state information for each of the carry elements to a time determining circuit that determines the time at which an event occurred based on the state information.

### Claim 12 (depends on 10)

The method according to claim 10, wherein the generating step further comprises generating delay by routing the delay signal through the activated one of the one or more delay modules and each delay module following the activated one of the one or more delay modules until the delay signal reaches a delay module designated as a final delay module.

### Claim 13 (depends on 12)

The method according to claim 12, wherein the final delay module has a feedback line connected thereto.

### Claim 14 (depends on 13)

The method according to claim 13, wherein the feedback line is connected to the signal generating circuit.

### Claim 15 (depends on 10)

The method according to claim 10, wherein the generating delaying further comprises:
generating delay by routing the start signal through a logic array block look-up table (LUT) of the activated one of the one or more delay modules.

### Claim 16

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.