Search

EP-4166979-B1 - OPTICAL DETECTION CIRCUIT AND DISTANCE MEASUREMENT DEVICE

EP4166979B1EP 4166979 B1EP4166979 B1EP 4166979B1EP-4166979-B1

Inventors

  • TSUKUDA, YASUNORI

Dates

Publication Date
20260506
Application Date
20210514

Claims (14)

  1. A photodetection circuit comprising: an avalanche photodiode (151); a charging circuit (152) that supplies a voltage to the avalanche photodiode; an input amplifier (154; 154a; 154b; 154c; 154d) including a comparison circuit (161; 161a; 164) in which a voltage level (Vs) of an output terminal of the input amplifier changes according to a comparison result between a voltage (Vc; Va) of an input terminal of the input amplifier connected to the avalanche photodiode (151) and a reference voltage (Vref; Vref1; Vref2), and a voltage control circuit (162; 162a; 163; 165; 174c,175c; 174d, 175d) that changes a potential of the reference voltage (Vref; Vref1; Vref2); and a state detecting circuit (155) that detects the voltage level (Vs) of the output terminal and sets timing for causing the voltage control circuit (162; 162a; 165; 174c, 175c; 174d, 175d) to change the potential of the reference voltage (Vref; Vref1; Vref2) on a basis of an output voltage (Vo) of the state detecting circuit (155) which is based on the detection result of the voltage level (Vs), wherein the state detecting circuit (155) includes inverter elements (190) of odd-numbered stages connected in series with one another, and wherein setting the timing for causing the voltage control circuit (162; 162a; 165; 174c, 175c; 174d, 175d) to change the potential of the reference voltage (Vref; Vref1; Vref2) includes outputting an output voltage (Vo) to the voltage control circuit (162; 162a; 165; 174c, 175c; 174d, 175d) after a predetermined delay time has elapsed, wherein the predetermined delay time is set on the basis of the number of inverter elements (190).
  2. The photodetection circuit according to claim 1, wherein the comparison circuit includes an inverter circuit (161; 170c-173c; 170d-173d), and the voltage control circuit (162; 174c, 175c; 174d, 175d) includes a switching element (174; 174c; 174d) that is connected to the inverter circuit (161; 170c-173c; 170d-173d) and performs switching according to the output voltage (Vo) of the state detecting circuit (155), and a resistive element (175; 175c; 175d) or a current source (175a) that is connected in parallel with the switching element (174; 174c; 174d).
  3. The photodetection circuit according to claim 1, wherein the comparison circuit includes an operational amplifier circuit (164), and the voltage control circuit includes a switch circuit (163; 165) that switches the reference voltage (Vref) to a first reference voltage (Vref1) or a second reference voltage (Vref2) different from the first reference voltage (Vref1) according to an output voltage (Vo) of the state detecting circuit (155).
  4. The photodetection circuit according to claim 1, wherein the comparison circuit includes an inverter circuit (161; 161a), and the voltage control circuit (162a; 163) includes a current source (175a; 176a) that is connected to the inverter circuit (161; 161a) and whose output current value changes according to an output voltage (Vo) of the state detecting circuit (155).
  5. The photodetection circuit according to any one of claims 1 to 4, wherein the input amplifier (154; 154a; 154b) includes a first input amplifier (154c) that outputs the comparison result to a signal processing circuit (143), and a second input amplifier (154d) that outputs the comparison result to the state detecting circuit (155).
  6. The photodetection circuit according to claim 5, wherein circuit configuration of the first input amplifier (154c) is same as circuit configuration of the second input amplifier (154d).
  7. The photodetection circuit according to claim 5, wherein circuit configuration of the first input amplifier (154c) is different from circuit configuration of the second input amplifier (154d).
  8. The photodetection circuit according to any one of claims 1 to 7, wherein the avalanche photodiode (151), the charging circuit (152), the input amplifier (154; 154a; 154b; 154c; 154d), and the state detecting circuit (155) are provided on one semiconductor substrate
  9. The photodetection circuit according to any one of claims 1 to 7, wherein the avalanche photodiode (151) is provided on a first semiconductor substrate (301), and the charging circuit (152), the input amplifier (154; 154a; 154b; 154c; 154d), and the state detecting circuit (155) are provided on a second semiconductor substrate (302) bonded to the first semiconductor substrate (301).
  10. The photodetection circuit according to any one of claims 1 to 9 further comprising a quench circuit (153) that is connected to the avalanche photodiode (151) and the input terminal of the input amplifier (154; 154a; 154b; 154c; 154d) and controls a potential of the input terminal.
  11. The photodetection circuit according to any one of claims 1 to 10, wherein a cathode of the avalanche photodiode (151) is connected to the input terminal of the input amplifier (154; 154a; 154b; 154c; 154d).
  12. The photodetection circuit according to any one of claims 1 to 10, wherein an anode of the avalanche photodiode (151) is connected to the input terminal of the input amplifier (154; 154a; 154b; 154c; 154d).
  13. A distance measuring device comprising: the photodetection circuit (142; 144) according to claim 1; and a signal processing circuit (143) that processes an output signal (Vs) of the photodetection circuit (142; 144).
  14. The distance measuring device according to claim 13, wherein the signal processing circuit (143) includes: a time to digital converter (TDC, 200) that converts the output signal into a digital value; a histogram creating section (201) that counts a number of times the digital value is acquired; and a distance determining section (202) that determines a distance from the photodetection circuit (142; 144) to a subject ( 102) on a basis of a count result of the histogram creating section (201).

Description

TECHNICAL FIELD The present disclosure relates to a photodetection circuit and a distance measuring device. BACKGROUND ART As a method of measuring the distance to a subject, a time of flight (ToF) method is used. In the ToF method, reflected light obtained by light emitted from a light source being reflected by a subject is detected. Subsequently, the distance to the subject is measured on the basis of the time from the emission of the light to the detection of the reflected light. A distance measuring device using the ToF method is generally provided with a photodetection circuit that detects the reflected light described above. In the photodetection circuit, a voltage change of a photodetection element obtained when photons are incident is detected. A reference voltage for detecting this voltage change is generally fixed. WO 2019/194039 A1 discloses an optical distance measuring apparatus using the ToF method. The disclosed distance measuring apparatus includes a light source that irradiates a target object with a light pulse having a first pulse width, a light receiver that outputs, at a second pulse width, a pulse signal representing reflected light from the irradiated target, and an adjuster that adjusts the first pulse width and/or the second pulse width so that the second pulse width is larger than or equal to the first pulse width. CITATION LIST PATENT DOCUMENT Patent Document 1: Japanese Patent Application Laid-Open No. 2014-81254 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION If the reference voltage described above is low, a distance measurement error increases due to characteristic variation of the photodetection element in some cases. In order to reduce this distance measurement error, it is desirable that the reference voltage be high. However, if the reference voltage is high, the dead time, which is a period during which photons cannot be detected, becomes long, and the distance measurement accuracy deteriorates in some cases. The present disclosure provides a photodetection circuit and a distance measuring device capable of improving distance measuring performance. SOLUTIONS TO PROBLEMS According to a first aspect, the present invention provides a photodetection circuit in accordance with independent claim 1. According to a second aspect, the present invention provides a distance measuring device in accordance with independent claim 13. Further aspects of the invention are set forth in the dependent claims, the drawings and the following description. A photodetection circuit comprising: an avalanche photodiode; a charging circuit that supplies a voltage to the avalanche photodiode; an input amplifier including a comparison circuit in which a voltage level (Vs) of an output terminal changes according to a comparison result between a voltage (Vc; Va) of an input terminal connected to the avalanche photodiode and a reference voltage (Vref; Vref1; Vref2), and a voltage control circuit that changes a potential of the reference voltage (Vref; Vref1; Vref2); and a state detecting circuit that detects the voltage level (Vs) of the output terminal and sets timing for causing the voltage control circuit to change the potential of the reference voltage (Vref; Vref1; Vref2) on a basis of an output voltage (Vo) of the state detecting circuit (155) which is based on the detection result of the voltage level (Vs), wherein the state detecting circuit includes inverter elements of odd-numbered stages connected in series with one another, and wherein setting the timing for causing the voltage control circuit to change the potential of the reference voltage (Vref; Vref1; Vref2) includes outputting an output voltage (Vo) to the voltage control circuit after a predetermined delay time has elapsed, wherein the predetermined delay time is set on the basis of the number of inverter elements. Furthermore, the comparison circuit may include an inverter circuit, and the voltage control circuit may include a switching element that is connected to the inverter circuit and performs switching according to an output voltage of the state detecting circuit, and a resistive element or a current source that is connected in parallel with the switching element. Furthermore, the comparison circuit may include an operational amplifier circuit, and the voltage control circuit may include a switch circuit that switches the reference voltage to a first reference voltage or a second reference voltage different from the first reference voltage according to an output voltage of the state detecting circuit. Furthermore, the comparison circuit may include an inverter circuit, and the voltage control circuit may include a current source that is connected to the inverter circuit and whose output current value changes according to an output voltage of the state detecting circuit. Furthermore, the state detecting circuit may include inverter elements of odd-numbered stages connected in series with one another. Furthermore,