Photodetector systems with low-power time-to-digital converter architectures to determine an arrival time of photon at a photodetector based on event detection time window

1. A system comprising:

a component configured to be worn on a body of a user, the component comprising a time-to-digital converter (TDC) configured to:

receive, during a predetermined event detection time window that commences in response to an application of a light pulse to a target within the body, a signal triggered by an event in which a photodetector detects a photon of the light pulse after the light pulse reflects from the target; and

measure, based on the receiving the signal, a time interval between when the event occurred and an end of the predetermined event detection time window; and

a processor configured to determine, based on the time interval and the predetermined event detection time window, an arrival time of the photon at the photodetector.

2. The system of claim 1 , wherein:

the signal is configured to enable a gated ring oscillator (GRO) of the TDC; and

the measuring is performed using the GRO.

3. The system of claim 2 , wherein the signal is further configured to:

enable the GRO of the TDC while the signal is being received by the TDC; and

disable the GRO of the TDC upon a stopping of the signal.

4. The system of claim 2 , wherein the TDC is further configured to receive, subsequent to the predetermined event detection time window, a second signal configured to disable the GRO of the TDC.

5. The system of claim 4 , wherein the second signal is received upon completion of the predetermined event detection time window.

6. The system of claim 2 , wherein:

the GRO includes one or more pairs of cross-coupled inverters configured to store a state of the GRO when the GRO is disabled; and

the measuring the time interval includes decoding the stored state of the GRO.

7. The system of claim 6 , wherein:

the TDC receives a voltage from a phase-locked loop (PLL) or a delay-locked loop (DLL) that provides an external reference clock; and

at least one of the enabling the GRO and the measuring the time interval is based additionally on the received voltage.

8. The system of claim 1 , wherein:

the TDC is further configured to measure an additional time interval subsequent to the time interval;

the processor is further configured to calibrate the TDC based on the measured additional time interval; and

the determining the arrival time of the photon is further based on the calibrating.

9. The system of claim 8 , wherein the additional time interval is a same or substantially similar length as the predetermined event detection time window.

10. The system of claim 8 , further comprising a calibration circuit configured to provide calculations for the calibrating the TDC.

11. The system of claim 8 , further comprising a lookup table configured to provide calculations for the calibrating the TDC.

12. The system of claim 1 , wherein:

the TDC is further configured to receive an event window signal specifying a starting time of the predetermined event detection time window; and

the determining the arrival time of the photon is further based on the starting time of the predetermined event detection time window.

13. The system of claim 1 , wherein the photodetector comprises:

a single photon avalanche diode (SPAD); and

a fast gating circuit configured to arm and disarm the SPAD.

14. The system of claim 1 , wherein the component is implemented by a non-invasive wearable brain interface system.

15. The system of claim 1 , further comprising a wearable battery configured to provide power to the component.

16. A system comprising:

a time-to-digital converter (TDC) configured to:

receive, during a predetermined event detection time window that commences in response to an application of a light pulse to a target, a signal triggered by an event in which a photodetector detects a photon of the light pulse after the light pulse reflects from the target; and

measure, based on the receiving the signal, a time interval between when the event occurred and an end of the predetermined event detection time window; and

a processor configured to determine, based on the time interval and the predetermined event detection time window, an arrival time of the photon at the photodetector.

17. The system of claim 1 , wherein:

the signal is configured to enable a gated ring oscillator (GRO) of the TDC; and

the measuring is performed using the GRO.

18. The system of claim 17 , wherein the signal is further configured to:

enable the GRO of the TDC while the signal is being received by the TDC; and

disable the GRO of the TDC upon a stopping of the signal.

19. The system of claim 17 , wherein the TDC is further configured to receive, subsequent to the predetermined event detection time window, a second signal configured to disable the GRO of the TDC.

20. A method comprising:

receiving, by a time-to-digital converter (TDC), during a predetermined event detection time window that commences in response to an application of a light pulse to a target, a signal triggered by an event in which a photodetector detects a photon of the light pulse after the light pulse reflects from the target;

measuring, by the TDC based on the receiving the signal, a time interval between when the event occurred and an end of the predetermined event detection time window; and

determining, based on the time interval and the predetermined event detection time window, an arrival time of the photon at the photodetector.