Hi LLC

Sebastian Sorgenfrei

Ryan Field

Jacob Dahle

Bruno Do Valle

Rong Jin

Isai Olvera

Hooman Mohseni

Husam Katnani

Haowen Ruan

Alex Borisevich

Katherine Perdue

Benjamin Siepser

Milin J Patel

Sangyong Park

Viswanath Ambalapuzha Gopalakrishnan

An illustrative optical measurement system includes a light source configured to emit a light pulse directed at a target. The optical measurement system further includes a plurality of photodetectors configured to operate in accordance with an input bias voltage. The optical measurement system further includes a control circuit configured to identify a photodetector subset included in the plurality of photodetectors and that detects, while the input bias voltage has a first value, photons of the light pulse after the light pulse is scattered by the target. The control circuit is further configured to determine, based on the identifying of the photodetector subset, an overvoltage associated with the photodetector subset. The control circuit is further configured to update, based on the overvoltage, the input bias voltage for the plurality of photodetectors to have a second value.

Maintaining consistent photodetector sensitivity in 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.

Techniques for determining a timing uncertainty of a component of an optical measurement system

An illustrative optical measurement system includes a light source configured to emit light directed at a target, an array of photodetectors configured to detect photons of the light after the light is scattered by the target, and a processing unit configured to measure a noise level of a photodetector included in the array of photodetectors, the noise level comprising a dark count rate that measures a dark count divided by a time period, determine that the noise level meets a predetermined threshold comprising a dark count rate threshold, and prevent, based on the determining that the noise level meets the predetermined threshold, an output of the photodetector from being used in generating a histogram based on a temporal distribution of photons detected by the array of photodetectors, the preventing comprising switching the output to a monitoring circuit that monitors a characteristic of the optical measurement system separate from the photodetector.

Photodetector calibration of an optical measurement system

An illustrative system may include a TDC configured to monitor for an occurrence of a photodetector output pulse during a measurement time window that is within and shorter in duration than a light pulse time period, the photodetector output pulse generated by a photodetector when the photodetector detects a photon from a light pulse having a light pulse time period; a PLL circuit for the TDC and having a PLL feedback period defined by a reference clock, the PLL circuit configured to: output a plurality of fine phase signals and output one or more signals representative of a plurality of feedback divider states during the PLL feedback period; and a precision timing circuit configured to adjust, based on one or more of the fine phase signals and/or the feedback divider states, a temporal position of the measurement time window within the light pulse time period.

Phase lock loop circuit based adjustment of a measurement time window in an optical measurement system

An illustrative 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 TDC included in the optical measurement system and generate, based on timestamp symbols recorded by the TDC in response to the signal, characterization data representative of a nonlinearity of the TDC.

Techniques for characterizing a nonlinearity of a time-to-digital converter in an optical measurement system

An illustrative optical measurement system includes a light source configured to emit light directed at a target. The optical measurement system further includes a photodetector configured to detect a photon of the light after the light is scattered by the target. The optical measurement system further includes a control circuit configured to receive a first input voltage that is a temperature-dependent voltage. The control circuit is further configured to receive a second input voltage that is a temperature-invariant voltage. The control circuit is further configured to output, based on a combination of the first input voltage and the second input voltage, a bias voltage for the photodetector, wherein the combination of the first and second input voltages is configured to cause the bias voltage to vary based on temperature.

An exemplary optical measurement system described herein includes a control circuit configured to output a global bias voltage and a module communicatively coupled to the control circuit. The module includes a light source configured to emit light directed at a target. The module further includes a plurality of detectors configured to detect arrival times for photons of the light after the light is scattered by the target. The module further includes a module control circuit configured to receive the global bias voltage and output a plurality of detector bias voltages based on the global bias voltage. The plurality of detector bias voltages include a respective detector bias voltage for each detector of the plurality of detectors.

Bias voltage generation in an optical measurement system

An illustrative optical measurement system includes a light source configured to emit light directed at a target, an array of photodetectors configured to detect photons of the light after the light is scattered by the target, and a processing unit. The processing unit is configured to measure a noise level of a photodetector included in the array of photodetectors and determine that the noise level meets a predetermined threshold. The processing unit is further configured to prevent, based on the determining that the noise level meets the predetermined threshold, an output of the photodetector from being used in generating a histogram based on a temporal distribution of photons detected by the array of photodetectors.

An exemplary system includes a processor, a wearable device comprising a plurality of slots, and a first module including a plurality of detectors and a module control circuit. The processor is configured to successively transmit, to each slot of the plurality of slots, a command to enable a respective module located in each slot. The processor is further configured to determine, based on an acknowledgment received from the module control circuit, that the first module is enabled and located in a first slot, and to successively transmit, based on the determining that the first module is enabled and located in the first slot, a plurality of detector address identifiers. The module control circuit is configured to successively place the plurality of detectors into an enumeration mode in which each detector of the plurality of detectors is assigned a different detector address identifier of the plurality of detector address identifiers.

Device enumeration in 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.

An exemplary optical measurement system includes a light source configured to emit light directed at a target. The optical measurement system further includes a photodetector configured to detect a photon of the light after the light is scattered by the target. The optical measurement system further includes a control circuit configured to receive a first input voltage that is a temperature-dependent voltage. The control circuit is further configured to receive a second input voltage that is a temperature-invariant voltage. The control circuit is further configured to output, based on a combination of the first input voltage and the second input voltage, a bias voltage for the photodetector, wherein the combination of the first and second input voltages is configured to cause the bias voltage to vary based on temperature.

An exemplary photodetector system includes a plurality of photodetectors connected in parallel and a processor communicatively coupled to the plurality of photodetectors. The processor is configured to receive an accumulated output from the plurality of photodetectors. The accumulated output represents an accumulation of respective outputs from each of the plurality of photodetectors detecting photons during a predetermined measurement time period that occurs in response to a light pulse being directed toward a target within a body. The processor is further configured to determine, based on the accumulated output, a temporal distribution of photons detected by the plurality of photodetectors, and generate, based on the temporal distribution of photons, a histogram representing a light pulse response of the target within the body.

Photodetector architectures for time-correlated single photon counting

An illustrative system may include 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. The system may further include 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.

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

An exemplary system includes a photodetector configured to generate a photodetector output pulse when the photodetector detects a photon from a light pulse having a light pulse time period, a TDC configured to monitor for the occurrence of the photodetector output pulse during a measurement time window that is within and shorter in duration than the light pulse time period, a PLL circuit for the TDC, and a precision timing circuit connected to the PLL circuit and configured to adjust, based on at least one signal generated within the PLL circuit, a temporal position of the measurement time window within the light pulse time period.

An exemplary system includes a PLL circuit and a precision timing circuit connected to the PLL circuit. The PLL circuit has a PLL feedback period defined by a reference clock and includes a voltage controlled oscillator configured to lock to the reference clock and having a plurality of stages configured to output a plurality of fine phase signals each having a different phase, and a feedback divider configured to be clocked by a single fine phase signal included in the plurality of fine phase signals and have a plurality of feedback divider states during the PLL feedback period. The precision timing circuit is configured to generate a timing pulse and set, based on a first combination of one of the fine phase signals and one of the feedback divider states, a temporal position of the timing pulse within the PLL feedback period.

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Playa Vista, CA, United States of America

Sebastian Sorgenfrei