Techniques for determining a timing uncertainty of a component of an optical measurement system
An illustrative system may include a memory storing instructions and a processor communicatively coupled to the memory and configured to execute the instructions to: cause a signal to be applied to a component within an 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. A system comprising:
a memory storing instructions; and
a processor communicatively coupled to the memory and configured to execute the instructions to:
cause a signal to be applied to a component within an 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 system of claim 1 , wherein:
the component is a time-to-digital converter (TDC);
the causing comprises directing a precision timing circuit to sweep a plurality of 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.
3. The system of claim 1 , wherein:
the component is a time-to-digital converter (TDC);
the causing comprises directing a precision timing circuit to apply a plurality of output pulses to the TDC; 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 characterization of an impulse response function of the TDC.
4. The system of claim 1 , wherein:
the causing comprises directing a light source to output light pulses;
the component is a photodetector configured to output a photodetector output pulse each time the photodetector detects a photon from the light pulses;
a time-to-digital converter (TDC) is configured to record a timestamp symbol each time the TDC detects an occurrence of the photodetector output pulse; and
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.
5. The system of claim 4 , wherein the performing of the action associated with the component comprises rating the photodetector based on the characterization data.
6. The system of claim 5 , 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.
7. A method comprising:
causing, by a processing unit, a signal to be applied to a component within an optical measurement system;
generating, by the processing unit based on a response of the component to the signal, characterization data representative of a timing uncertainty associated with the component; and
performing, by the processing unit based on the characterization data, an action associated with the component.
8. The method of claim 7 , wherein the component is one or more of a photodetector or 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.
9. The method of claim 8 , wherein:
the component is the TDC;
a 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 causing the signal to be applied 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.
10. The method of claim 9 , wherein the performing the action associated with the component comprises compensating for one or more irregularities in the transfer curve.
11. The method of claim 9 , wherein:
the TDC is included in an array of TDCs; and
the method further comprises disabling other TDCs within the array of TDCs while the signal is being applied to the TDC.
12. The method of claim 8 , further comprising passing, by a multiplexer included in the optical measurement system and to the TDC, the signal or a photodetector output pulse generated by the photodetector.
13. The method of claim 12 , wherein:
the component is the TDC;
the method further comprises directing the multiplexer to pass the signal to the TDC.
14. The method of claim 12 , wherein the signal or the photodetector output pulse is passed to the TDC by way of an output buffer in series with an output of the multiplexer and the TDC.
15. The method of claim 8 wherein:
the component is the TDC;
a 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 causing the signal to be applied 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.
16. The method of claim 15 , wherein:
the TDC is included in an array of TDCs; and
the method further comprises disabling other TDCs within the array of TDCs while the signal is being applied to the TDC.
17. The method of claim 15 , wherein the performing of the action associated with the component comprises rating the TDC based on the characterization data.
18. The method of claim 8 , wherein the photodetector comprises a single photon avalanche diode (SPAD).
19. The method of claim 7 , the processing unit is included in a head-mountable component configured to be worn on a head of a user.
20. The method of claim 7 , wherein the causing, generating, and performing are performed while the optical measurement system is in a calibration mode.