Systems for CMOS-compatible three-dimensional image sensing using quantum efficiency modulation

• US 20030076484A1
• Filed: 12/11/2001
• Published: 04/24/2003
• Est. Priority Date: 11/09/2000
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Canesta Incorporated (Microsoft Corporation)
• Inventors: Charbon, Edoardo, Bamji, Cyrus
• Granted Patent: US 6,580,496 B2
• Time in Patent Office: Days
• US Class Current: 356/5.1
• CPC Class Codes: G01S 17/36 with phase comparison between the received signal and the contemporaneously transmitted signal
• CPC Class Codes: G01S 17/894 3D imaging with simultaneous measurement of time-of-flight at a 2D array of receiver pixels, e.g. time-of-flight cameras or flash lidar
• CPC Class Codes: G01S 7/4914 of detector arrays, e.g. charge-transfer gates

Abstract

A preferably CMOS-implementable system measures distance and/or brightness by illuminating a target with emitted optical energy having a modulated periodic waveform whose high frequency component may be idealized as S₁=cos(ω·t). A fraction of the emitted optical energy is reflected by a target and detected with at least one in a plurality of semiconductor photodetectors. Photodetector quantum efficiency is modulated to process detected signals to yield data proportional to the distance z separating the target and photodetector. Detection includes measuring phase change between the emitted optical energy and the reflected fraction thereof. Quantum efficiency can be modulated with fixed or variable phase methods and may be enhanced using enhanced photocharge collection, differential modulation, and spatial and temporal multiplexing. System power requirements may be reduced with inductors that resonate with photodetector capacitance at the operating frequency. The system includes on-chip photodetectors, associated electronics, and processing.

Claims

1. A system to determine distance z between at least one photodetector, and a target, the system comprising:

a source of optical energy that emits a modulated periodic waveform having high frequency component S₁(ω

·

t);

a plurality of photodetectors, disposed to detect a fraction of said optical energy reflected from said target; and

means for modulating quantum efficiency of said photodetector to process photodetector detected signals to yield data proportional to said distance z.

2. The system of claim 1, wherein said plurality of photodetectors and said means for modulating are fabricated on a single integrated circuit chip.

3. The system of claim 1, wherein said plurality includes at least one of (i) photodiode detectors, (ii) MOS devices with a bias gate, and (iii) MOS devices with a photogate.

4. The system of claim 1, further including a circuit to measure change in phase between emitted optical energy and a signal detected by at least some of said photodetectors.

5. The system of claim 1, further including a variable phase delay circuit, coupled to a source of said modulated periodic waveform, operating in a closed-loop, such that phase delay of said variable phase delay indicates phase delay of a photodetector detected signal relative to phase of emitted optical energy.

6. The system of claim 1, further including a circuit to measure change in phase between optical energy emitted by said source of optical energy, and a signal detected by at least some said photodetectors, said circuit using at least one fixed phase delay.

7. The system of claim 4, wherein said change of phase is proportional to said distance z.

8. The system of claim 1, wherein said means for modulating varies reverse bias of said photodetectors

9. The system of claim 1, wherein said photodetectors include photogate detectors, and said means for modulating varies gate potential of said photogate detectors.

10. The system of claim 1, further including:

circuitry to measure a change in phase between optical energy emitted by said source of optical energy, and a signal detected by said photodetectors;

banks of said photodetectors;

wherein said means for modulating modulates said banks of said photodetectors with different phases.

11. The system of claim 1, wherein said photodetectors are formed on a semiconductor substrate;

and

further including means for creating an electrical current in said substrate to promote collection of photocharges released within said substrate by reflected said optical energy;

wherein quantum efficiency modulation is enhanced.

12. The system of claim 1, wherein:

said photodetectors are formed on a semiconductor substrate including an epitaxial region, said epitaxial region of said substrate has at least one characteristic selected from (i) said epitaxial region comprises a plurality of layers each having a different doping concentration, wherein an uppermost one of said layers is less highly doped than a lower one of said layers, (ii) said epitaxial region defines a layer in which there is a dopant gradient such that doping concentration is greater at a lower portion of said region than at an upper portion thereof.

13. The system of claim 1, further including:

an inductor coupled so as to detune at least a fraction of capacitance coupled to a voltage node of said photodetectors controlling quantum efficiency modulation thereof;

wherein power dissipation of said capacitance is reduced.

14. The system of claim 1, further including:

a first bank of said photodetectors;

a second bank of said photodetectors;

said means for modulating being quantum efficiency modulating said first bank and said second bank with a constant phase;

at least one pixel comprising a photodetector from said first bank and a photodetector from said second bank;

wherein said circuit processes an output from one said photodetector for use by more than one said pixel.

15. The system of claim 1, wherein:

said system determines distance z over multiple time frames; and

on a per frame basis, said means for modulating quantum efficiency modulates said photodetector with at least a first phase shift, and acquires information from said photodetector during said first phase shift; and

information acquired from said photodetector during said first phase shift is used in at least two said time frames.

16. The system of claim 1, further including means for digitizing an analog output from each said photodetector.

17. The system of claim 1, wherein said frequency ω

is at least 100 MHz.

18. The system of claim 1, wherein emitted said optical energy has a wavelength of about 850 nm.

19. A CMOS-implementable integrated circuit to measure distance z between a source of optical energy controlled by said system and a target, said integrated circuit comprising:

a generator, coupleable to a source of said optical energy that emits a modulated periodic waveform having high frequency component S₁(ω

·

t);

a plurality of photodetectors, disposed to detect a fraction of said optical energy reflected from said target; and

means for modulating quantum efficiency of said photodetector to process photodetector detected signals to yield data proportional to said distance z.

20. The integrated circuit of claim 19, wherein said plurality includes at least one of (i) photodiode detectors, (ii) MOS devices with a bias gate, and (iii) MOS devices with a photogate.

21. The integrated circuit of claim 19, further including a circuit to measure change in phase between emitted optical energy and a signal detected by at least some of said photodetectors.

22. The integrated circuit of claim 19, further including a variable phase delay circuit, coupled to a source of said modulated periodic waveform, operating in a closed-loop, such that phase delay of said variable phase delay indicates phase delay of a photodetector detected signal relative to phase of emitted optical energy.

23. The integrated circuit of claim 19, further including a circuit to measure change in phase between optical energy emitted by said source of optical energy, and a signal detected by at least some said photodetectors, said circuit using at least one fixed phase delay.

24. The integrated circuit of claim 21, wherein said change of phase is proportional to said distance z.

25. The integrated circuit of claim 19, wherein said means for modulating varies reverse bias of said photodetectors

26. The integrated circuit of claim 19, wherein said photodetectors include photogate detectors, and said means for modulating varies gate potential of said photogate detectors.

27. The integrated circuit of claim 19, further including:

circuitry to measure a change in phase between optical energy emitted by said source of optical energy, and a signal detected by said photodetectors;

banks of said photodetectors;

wherein said means for modulating modulates said banks of said photodetectors with different phases.

28. The integrated circuit of claim 19, further including:

means for creating an electrical current in said substrate to promote collection of photocharges released within said substrate by reflected said optical energy;

wherein quantum efficiency modulation is enhanced.

29. The integrated circuit of claim 19, further including:

a bias circuit to create an electrical current in said substrate to promote collection of photocharges released within said substrate by reflected said optical energy;

wherein quantum efficiency modulation is enhanced.

30. The integrated circuit of claim 19, wherein said photodetectors are formed on a semiconductor substrate including an epitaxial region, said epitaxial region of said substrate has at least one characteristic selected from (i) said epitaxial region comprises a plurality of layers each having a different doping concentration, wherein an uppermost one of said layers is less highly doped than a lower one of said layers, (ii) said epitaxial region defines a layer in which there is a dopant gradient such that doping concentration is greater at a lower portion of said region than at an upper portion thereof.

31. The integrated circuit of claim 19, further including:

an inductor coupled so as to detune at least a fraction of capacitance coupled to a voltage node of said photodetectors controlling quantum efficiency modulation thereof;

wherein power dissipation of said capacitance is reduced.

32. The integrated circuit of claim 19, further including:

a first bank of said photodetectors;

a second bank of said photodetectors;

said means for modulating being quantum efficiency modulating said first bank and said second bank with a constant phase;

at least one pixel comprising a photodetector from said first bank and a photodetector from said second bank;

wherein said circuit processes an output from one said photodetector for use by more than one said pixel.

33. The integrated circuit of claim 19, wherein:

said system determines distance z over multiple time frames; and

on a per frame basis, said means for modulating quantum efficiency modulates said photodetector with at least a first phase shift, and acquires information from said photodetector during said first phase shift; and

information acquired from said photodetector during said first phase shift is used in at least two said time frames.

34. The integrated circuit of claim 19, further including a microprocessor controlling operation of at least said means for modulating.

35. The integrated circuit of claim 19, further including means for digitizing an analog output from each said photodetector.

36. The integrated circuit of claim 19, wherein said frequency ω

is at least 100 MHz.

37. The integrated circuit of claim 19, wherein emitted said optical energy has a wavelength of about 850 nm.