Multiplexed multichannel photodetector

Patent metadata

Field	Value
Publication number	US-9529079-B1
Application number	US-201514669109-A
Country	US
Kind code	B1
Filing date	Mar 26, 2015
Priority date	Mar 26, 2015
Publication date	Dec 27, 2016
Grant date	Dec 27, 2016

Abstract

A light detection and ranging (LIDAR) system can emit light toward an environment and detect responsively reflected light to determine a distance to one or more points in the environment. The reflected light can be detected by a plurality of plurality of photodiodes that are reverse-biased using a high voltage. Signals from the plurality of reverse-biased photodiodes can be amplified by respective transistors and applied to an analog-to-digital converter (ADC). The signal from a particular photodiode can be applied to the ADC by biasing a respective transistor corresponding to the particular photodiode while not biasing transistors corresponding to other photodiodes. The gain of each photodiode/transistor pair can be controlled by adjusting the bias voltage applied to each photodiode using a digital-to-analog converter. The gain of each photodiode/transistor pair can be controlled based on the detected temperature of each photodiode.

First claim

What is claimed is:

1. A system comprising:
an analog-to-digital converter;
at least one photodiode biasing voltage source;
a plurality of photodetector channels, wherein each photodetector channel comprises:
a photodiode coupled to the at least one photodiode biasing voltage source, wherein the photodiode is configured to provide a photodiode signal indicative of light incident on the photodiode when the photodiode is reverse-biased by the at least one photodiode biasing voltage source;
a capacitor coupled to the photodiode; and
a transistor, wherein the transistor has an input coupled to the photodiode via the capacitor and an output coupled to the analog-to-digital converter, and wherein the transistor is configured to amplify the photodiode signal to provide an amplified photodiode signal at the output when the transistor is operationally biased; and

a channel selector, wherein the channel selector is configured to individually select each respective photodetector channel in the plurality of photodetector channels by operationally biasing the respective transistor in the selected photodetector channel.

2. The system of claim 1 , wherein the respective transistor in each photodetector channel is a bipolar transistor.

3. The system of claim 1 , wherein the respective transistor in each photodetector channel is a silicon-germanium transistor.

4. The system of claim 1 , wherein the respective transistor in each photodetector channel is coupled to an amplifier voltage source via an amplifier source impedance, wherein the amplifier source impedance is configured to maximize the gain of the respective transistor of each photodetector channel such that the respective transistor of each photodetector channel operates with a bandwidth less than approximately 100 megahertz when the respective transistor of each photodetector channel is operationally biased by the channel selector.

5. The system of claim 1 , wherein each photodetector channel further comprises a respective Schottky diode and a respective bias resistor coupled in parallel between the input of the respective transistor of each photodetector channel and the channel selector, wherein the cathode of the Schottky diode is coupled to the channel selector, and wherein the channel selector operationally biasing a particular transistor comprises providing a biasing voltage to the input of the particular transistor via the respective Schottky diode and respective bias resistor.

6. The system of claim 1 , wherein the respective photodiode of each photodetector channel is an avalanche photodiode.

7. The system of claim 6 , wherein the at least one photodiode biasing voltage source provides a voltage between approximately 150 volts and approximately 250 volts.

8. The system of claim 1 , wherein the voltage provided by the at least one photodiode biasing voltage source is controllable.

9. The system of claim 1 , further comprising a temperature sensor configured to detect the temperature of at least one respective photodiode of the plurality of photodetector channels.

10. The system of claim 1 , wherein each photodetector channel further comprises a respective digital-to-analog converter coupled to the respective photodiode of each photodetector channel via a respective resistor, wherein each digital-to-analog converter is configured to adjust a respective reverse-bias voltage applied to the respective photodiode by the at least one photodiode biasing voltage source.

11. The system of claim 10 , wherein each digital-to-analog converter is configured to adjust the respective reverse-bias voltage by at least approximately 50 volts.

12. The system of claim 1 , wherein the channel selector comprises a plurality of electronic switches, wherein each electronic switch of the channel selector is coupled to the input of the respective transistor of each photodetector channel via a respective biasing resistor, wherein the channel selector operationally biasing the respective transistor in the selected photodetector channel comprises the channel selector operating the respective electronic switch to provide a biasing voltage, and wherein the respective electronic switch, respective biasing resistor, and respective transistor for each photodetector channel are physically proximate.

13. A method comprising:
selecting, during a first period of time, a first photodetector channel of a system, wherein the system comprises:
an analog-to-digital converter;
at least one photodiode biasing voltage source;
a plurality of photodetector channels, wherein each photodetector channel comprises:
a photodiode coupled to the at least one photodiode biasing voltage source, wherein the photodiode is configured to provide a photodiode signal indicative of light incident on the photodiode when the photodiode is reverse-biased by the at least one photodiode biasing voltage source;
a capacitor coupled to the photodiode; and
a transistor, wherein the transistor has an input coupled to the photodiode via the capacitor and an output coupled to the analog-to-digital converter, and wherein the transistor is configured to amplify the photodiode signal to provide an amplified photodiode signal at the output when the transistor is operationally biased; and

a channel selector, wherein the channel selector is configured to individually select each respective photodetector channel in the plurality of photodetector channels by operationally biasing the respective transistor in the selected photodetector channel; wherein selecting the first photodetector channel comprises operating the channel selector to operationally bias the respective transistor of the first photodetector channel;

detecting, during the first period of time, light received by the respective photodiode of the first photodetector channel by detecting the output of the respective transistor of the first photodetector channel using the analog-to-digital converter;
selecting, during a second period of time, a second photodetector channel of the system, wherein selecting the second photodetector channel comprises operating the channel selector to operationally bias the respective transistor of the second photodetector channel; and
detecting, during the second period of time, light received by the respective photodiode of the second photodetector channel by detecting the output of the respective transistor of the second photodetector channel using the analog-to-digital converter.

14. The method of claim 13 , wherein a switching time between the first period of time and the second period of time has a duration that is less than approximately 100 nanoseconds.

15. The method of claim 13 , further comprising:
illuminating an environment with a pulse of illumination emitted from a light source of the system, wherein the respective photodiode of the first photodetector channel is configured to receive the pulse of emitted illumination reflected from the environment;
determining the timing of a pulse of illumination received by the respective photodiode of the first photodetector channel relative to the pulse of emitted illumination based on the output of the respective transistor of the first photodetector channel detected using the analog-to-digital converter during the first period of time.

16. The method of claim 15 , further comprising:
determining the distance from the light source to an aspect of the environment illuminated by the pulse of emitted illumination based on the determined timing of the pulse of illumination received by the respective photodiode of the first photodetector channel.

17. The

Assignees

• Google Inc

Inventors

• Droz Pierre Yves
• Lenius Samuel William

Classifications

• H04N25/77

  Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components · CPC title

• H04N25/40

  Extracting pixel data from image sensors by controlling scanning circuits, e.g. by modifying the number of pixels sampled or to be sampled · CPC title

• H04N25/772

  comprising A/D, V/T, V/F, I/T or I/F converters · CPC title

• H04N25/773

  comprising photon counting circuits, e.g. single photon detection [SPD] or single photon avalanche diodes [SPAD] · CPC title

• H04N5/341

  Electricity · mapped topic