Techniques for determining a timing uncertainty of a component of an optical measurement system
An exemplary optical measurement system includes a signal generator configured to generate a signal and a processing unit configured to direct the signal generator to apply the signal to a component within the optical measurement system, generate, based on a response of the component to the signal, characterization data representative of a timing uncertainty associated with the component, and perform, based on the characterization data, an action associated with the component.
1. An optical measurement system comprising:
a signal generator configured to generate a signal; and
a processing unit configured to
direct the signal generator to apply the signal to a component within the optical measurement system,
generate, based on a response of the component to the signal, characterization data representative of a timing uncertainty associated with the component, and
perform, based on the characterization data, an action associated with the component.
2. The optical measurement system of claim 1 , further comprising:
a photodetector; and
a time-to-digital converter (TDC) configured to measure a time difference between an occurrence of a light pulse and an occurrence of a photodetector output pulse generated by the photodetector, the photodetector output pulse indicating that the photodetector has detected a photon from the light pulse after the light pulse is scattered by a target;
wherein the component is one or more of the photodetector or the TDC.
3. The optical measurement system of claim 2 , wherein:
the component is the TDC;
the signal generator comprises
a phase lock loop (PLL) circuit having a PLL feedback period, and
a precision timing circuit configured to generate output pulses having programmable temporal positions within the PLL feedback period, the signal comprising a sequence of the output pulses;
the directing of the signal generator to apply the signal to the component comprises directing the precision timing circuit to sweep the output pulses across a plurality of temporal positions; and
the generating of the characterization data comprises generating, based on timestamp symbols recorded by the TDC in response to the output pulses, data representative of a transfer curve that represents a characterization of one or more nonlinearities of the TDC.
4. The optical measurement system of claim 3 , wherein the performing of the action associated with the component comprises compensating for one or more irregularities in the transfer curve.
5. The optical measurement system of claim 3 , wherein:
the TDC is included in an array of TDCs; and
the processing unit is configured to disable other TDCs within the array of TDCs while the signal is being applied to the TDC.
6. The optical measurement system of claim 2 , further comprising a multiplexer configured to selectively pass, to the TDC, the signal or a photodetector output pulse generated by the photodetector.
7. The optical measurement system of claim 6 , wherein:
the component is the TDC;
the processing unit is configured to direct the multiplexer to pass the signal to the TDC.
8. The optical measurement system of claim 6 , further comprising an output buffer in series with an output of the multiplexer and the TDC, wherein the signal or the photodetector output pulse is passed to the TDC by way of the output buffer.
9. The optical measurement system of claim 2 , wherein:
the component is the TDC;
the signal generator comprises
a phase lock loop (PLL) circuit having a PLL feedback period, and
a precision timing circuit configured to generate output pulses each having a same programmable temporal position within the PLL feedback period, the signal comprising a sequence of the output pulses;
the directing of the signal generator to apply the signal to the component comprises directing the precision timing circuit to apply the output pulses to the TDC; and
the generating of the characterization data comprises generating, based on a variation in timestamp symbols recorded by the TDC in response to the output pulses, data representative of a characterization of an impulse response function of the TDC.
10. The optical measurement system of claim 9 , wherein:
the TDC is included in an array of TDCs; and
the processing unit is configured to disable other TDCs within the array of TDCs while the signal is being applied to the TDC.
11. The optical measurement system of claim 9 , wherein the performing of the action associated with the component comprises rating the TDC based on the characterization data.
12. The optical measurement system of claim 2 , wherein:
the component is the photodetector;
the signal generator comprises a light source configured to output a plurality of light pulses;
the directing of the signal generator to apply the signal to the component comprises directing the light source to output the light pulses; and
the photodetector is configured to output a photodetector output pulse each time the photodetector detects a photon from the light pulses;
the TDC is configured to record a timestamp symbol each time the TDC detects an occurrence of the photodetector output pulse;
the generating of the characterization data comprises generating, based on a variation in the timestamp symbols recorded by the TDC, data representative of a characterization of an impulse response function of the photodetector.
13. The optical measurement system of claim 12 , wherein the performing of the action associated with the component comprises rating the photodetector based on the characterization data.
14. The optical measurement system of claim 12 , wherein the performing of the action associated with the component comprises:
determining that a value of the characterization data is outside a predetermined range of values; and
disabling, in response to the determining that the value is outside the predetermined range of values, the photodetector.
15. The optical measurement system of claim 12 , wherein:
the photodetector is included in an array of photodetectors; and
the processing unit is configured to disable other photodetectors within the array of photodetectors while the light pulses are being applied to the photodetector.
16. The optical measurement system of claim 2 , wherein the photodetector comprises a single photon avalanche diode (SPAD).
17. The optical measurement system of claim 1 , further comprising a head-mountable component configured to be worn on a head of a user, wherein one or more of the signal generator or the processing unit are included in the head-mountable component.
18. The optical measurement system of claim 1 , wherein:
the processing unit is configured to place the optical measurement system in a calibration mode; and
the directing, generating, and performing are performed while the optical measurement system is in the calibration mode.