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

• US 6,515,740 B2
• Filed: 12/11/2001
• Issued: 02/04/2003
• Est. Priority Date: 11/09/2000
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Canesta Incorporated (Microsoft Corporation)
• Inventors: Charbon, Edoardo, Bamji, Cyrus
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US10/020,393
• Publication Number:
  US 20020084430A1
• Time in Patent Office: 420 Days
• Field of Search: 356/141.1, 356/5.1, 356/4.01
• US Class Current: 356/141.1
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• 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
• CPC Class Codes: G01S 7/4915 Time delay measurement, e.g. operational details for pixel components signal extraction and conditioning G01S7/493; Phase measurement
• CPC Class Codes: G01S 7/493 Extracting wanted echo signals

Abstract

A preferably CMOS-implementable method 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 method can be implemented with on-chip photodetectors, associated electronics, and processing.

Claims

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

(a) illuminating said target with optical energy that has a modulated periodic waveform that includes a high frequency component S₁(ω

·

t);

(b) detecting with said photodetector a fraction of said optical energy reflected from said target; and

(c) modulating quantum efficiency of said photodetector to process signals detected at step (b) to yield data proportional to said distance z.

2. The method of claim 1, further including a plurality of photodetectors fabricated on an integrated circuit chip;

wherein said integrated circuit chip includes circuitry that carries out step (b) and step (c).

3. The method 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 method of claim 1, wherein detecting at step (b) includes measuring a change in phase between optical energy emitted at step (a) and a signal detected at step (b).

5. The method of claim 4, wherein step (c) includes using a variable phase delay that is 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 signal detected at step (b).

6. The method of claim 4, wherein step (c) includes use of at least one fixed phase delay.

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

8. The method of claim 1, wherein step (c) includes varying reverse bias of said photodetectors.

9. The method of claim 1, wherein said photodetectors include photogate detectors, and step (c) includes varying gate potential of said photogate detectors.

10. The method of claim 1, wherein:

detecting at step (b) includes measuring a change in phase between optical energy emitted at step (a) and a signal detected at step (b);

further including;

defining banks of said photodetectors; and

enhancing efficiency of said quantum efficiency modulation by modulating banks of said photodetectors with different phases.

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

and

step (c) includes 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 method of claim 1, wherein said photodetectors are formed on a semiconductor substrate including an epitaxial region;

and

step (c) includes using a substrate whose said epitaxial region 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 method of claim 1, further including coupling an inductor so as to detune at least some capacitance coupled to a voltage node of said detector controlling quantum efficiency modulation thereof;

wherein power dissipation of said capacitance is reduced.

14. The method of claim 1, further including:

defining at least a first bank of said photodetectors and a second bank of said photodetectors, each said bank being quantum efficiency modulated with a constant phase;

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

wherein step (c) includes processing an output from one said photodetector for use by more than one said pixel.

15. The method of claim 1, wherein:

distance z in determined over multiple time frames; and

claim (c) further includes;

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

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

16. The method of claim 1, further including:

digitizing an analog output from each said photodetector.

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

is at least 100 MHz.

18. The method of claim 1, further including providing an integrated circuit that includes electronic circuitry that carries out at least one of step (b) and step (c).

19. The method of claim 1, wherein step (a) includes illuminating said target with optical energy having wavelength of about 850 nm.

20. A method to determine amplitude of a fraction of emitted optical energy that is reflected from a target, the method comprising the following steps:

(a) illuminating said target with optical energy that has a modulated periodic waveform that includes a high frequency component S₁(ω

·

t);

(b) providing at least one photodetector to detect said fraction of optical energy reflected by said target;

(c) detecting with said photodetector said fraction of said optical energy reflected from said target; and

(d) modulating quantum efficiency of said photodetector to process signals detected at step (c) to yield data proportional to amplitude.

21. The method of claim 20, wherein said frequency ω

is at least 100 Hz.

22. The method of claim 20, wherein step (a) includes illuminating said target with optical energy having wavelength of about 850 nm.