Noise reduction techniques suitable for three-dimensional information acquirable with CMOS-compatible image sensor ICS

• US 6,522,395 B1
• Filed: 11/28/2000
• Issued: 02/18/2003
• Est. Priority Date: 04/30/1999
• Status: Expired due to Term

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Canesta Incorporated (Microsoft Corporation)
• Inventors: Charbon, Edoardo, Bamji, Cyrus, Shivji, Shiraz
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US09/727,529
• Time in Patent Office: 812 Days
• Field of Search: 356/141.1, 356/5-1-
• US Class Current: 356/5.01
• CPC Class Codes: G01C 3/08 Use of electric radiation detectors
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/14 wherein a voltage or current pulse is initiated and terminated in accordance with the pulse transmission and echo reception respectively, e.g. using counters
• CPC Class Codes: G01S 17/46 Indirect determination of position data
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4802 using analysis of echo signal for target characterisation; Target signature; Target cross-section
• CPC Class Codes: G01S 7/486 Receivers
• CPC Class Codes: G01S 7/4865 Time delay measurement, e.g. time-of-flight measurement, time of arrival measurement or determining the exact position of a peak peak detection in noise, signal conditioning G01S7/487
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating
• CPC Class Codes: G06F 1/1626 with a single-body enclosure integrating a flat display, e.g. Personal Digital Assistants [PDAs]
• CPC Class Codes: G06F 1/1632 External expansion units, e.g. docking stations
• CPC Class Codes: G06F 3/011 Arrangements for interaction with the human body, e.g. for user immersion in virtual reality blind teaching G09B21/00
• CPC Class Codes: G06F 3/0221 Arrangements for reducing keyboard size for transport or storage, e.g. foldable keyboards, keyboards with collapsible keys G06F3/0216 takes precedence; for keyboards integrated in a laptop computer G06F1/1666
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen
• CPC Class Codes: G06V 30/228 of three-dimensional handwriting, e.g. writing in the air
• CPC Class Codes: H04N 25/53 Control of the integration time
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

A three-dimensional imaging system is fabricated on a single IC. The system includes a two-dimensional array of pixel light sensing detectors and dedicated electronics and associated processing circuitry, all preferably fabricated on a single IC using CMOS fabrication techniques. The system includes a detector array comprising a plurality of pixel photodiodes and photodiode circuits, wherein each pixel photodiode acquires delay time data and pulse brightness data simultaneously. The system emits an energy pulse at time t0 and a fraction of the energy is returned to the array by a target object. Photodiodes in the array output a brightness signal B(t) that is integrated. An elapsed time ET from t0 to when said B(t) attains a predetermined threshold value is determined, where the slope of B(t) is B/PW, where B is B(t) after integrating over a time equal to the emitted pulse width PW. Time-of-flight TOF representing time from t0 to when a photodiode begins to detect energy is determined, where TOF=ET−IT, where IT is proportional to PW/B. A system processor determines distance from the system to the target object, from TOF and the velocity of light, and can translate TOF into commands to control electronic devices.

Claims

1. A method to determine distance Z within resolution Δ

Z between at least one pixel photodiode detector and a target less than about 100 m distant, the method comprising the following steps;

(a) at time t0 emitting toward said target at least a first pulse of optical energy having a pulse width PW from an optical energy source;

(b) disposing at least one pixel photodiode detector so as to detect optical energy reflected from said target, where each said pixel photodiode detector has an associated pixel photodiode detector circuit, each said pixel photodiode detector having an integration delay time exceeding 2·

Δ

Z/C, where C is speed of light;

(c) integrating a detected brightness signal B(t) output from each said pixel photodiode detector responsive to detection of at least some reflected said optical energy and determining an elapsed time ET from t0 to when said B(t) attains a predetermined threshold value, wherein slope of B(t) is B/PW, where B is magnitude of B(t) after integrating over a time equal to PW;

(d) determining time-of-flight TOF representing time from t0 to when said photodiode begins to detect at least some reflected said optical energy, where TOF=ET−

IT, where IT is integration time and is proportional to PW/B; and

(e) determining from said TOF and from C a distance from each said pixel photodiode detector to a portion of said target reflecting said optical energy;

wherein said pixel photodiode detector acquires delay time data and pulse brightness data simultaneously.

2. The method of claim 1, wherein said delay time data is time for light to travel from said optical energy source to said target and be reflected to said pixel photodiode detector and to build-up detectable signal strength at said pixel photodiode detector.

3. The method of claim 1, wherein said pulse brightness data is total signal detected from at least one said pulse of optical energy detected by said pixel photodiode detector.

4. The method of claim 1, wherein:

step (b) includes disposing an array of pixel photodiode detectors so as to detect optical energy reflected from said target, each of said pixel photodiode detectors having an associated pixel photodiode detector circuit; and

providing means for accumulating overtime a number N of signal samples from each said pixel photodiode detectors;

wherein measurement accuracy is enhanced proportional to N.

5. The method of claim 1, wherein:

step (b) includes disposing an array of pixel photodiode detectors so as to detect optical energy reflected from said target, each of said pixel photodiode detectors having an associated pixel photodiode detector circuit; and

said array comprises Y·

Y pixel photodiode detectors and Y·

Y pixel photodiode detector circuits, where Y is an integer greater than ten.

6. The method of claim 1, wherein step (c) includes integrating by coupling an output from said pixel photodiode detector to a first capacitor.

7. The method of claim 6, wherein step (c) includes integrating differentially using a second voltage-tunable capacitor matched within a tolerance of about ±

2% to said first capacitor.

8. The method of claim 1, wherein:

integration at step (c) is carried out by said pixel photodiode detector circuit, said pixel photodiode detector circuit including KT/C offset reduction architecture.

9. A CMOS-implementable integrated circuit (IC) time of flight (TOF) measurement system used with an optical pulse source to determine distance Z within resolution Δ

Z between said IC and a target, the IC including;

an array of pixel photodiode detectors to detect reflected optical pulse energy returned from said target, said pixel photodiode detectors able to acquire delay time data and pulse brightness data simultaneously and having an integration delay time exceeding 2·

Δ

Z/C, where C is speed of light;

for each of said pixel photodiode detectors, an associated pixel photodiode detector circuit that includes;

means for integrating a detected brightness signal B(t) output from each said pixel photodiode detector responsive to detection of at least some reflected said optical energy, where said IC causes a pulse of optical energy to be emitted at time t0;

means for determining an elapsed time ET from t0 to when said B(t) attains a predetermined threshold value, wherein slope of B(t) is B/PW, where B is magnitude B(t) after integrating over a time equal to PW;

means for determining time-of-flight TOF representing time from t0 to when said pixel photodiode detector begins to detect at least some reflected said optical energy, where TOF=ET−

IT, where IT is integration time and is proportional to PW/B;

said IC further including a processor unit to determine from said TOF and from C a distance from each said pixel photodiode detector to a portion of said target reflecting said optical energy.

10. The IC of claim 9, wherein said delay time data is time for light to travel from said optical pulse source to said target and be reflected to said pixel photodiode detector and to build-up detectable signal strength at said pixel photodiode detector.

11. The IC of claim 9, wherein said pulse brightness data is total signal detected from at least one said pulse of optical energy detected by one said pixel photodiode detector.

12. The IC of claim 9, further including means for accumulating over time a number N of signal samples from each of said pixel photodiode detectors;

wherein measurement accuracy is enhanced proportional to N.

13. The IC of claim 9, wherein said IC includes a detector array comprising Y·

Y pixel photodiode detectors and Y·

Y pixel photodiode detector circuits, where Y is an integer greater than ten.

14. The IC of claim 9, wherein said means for integrating includes coupling an output from each said pixel photodiode detector to a first capacitor in an associated said photodiode detector circuit.

15. The IC of claim 14, wherein said means for integrating includes a differential integrator comprising a second voltage-tunable capacitor matched within a tolerance of about ±

2% to said first capacitor.

16. The IC of claim 9, wherein each said pixel photodiode detector circuit includes means for reducing KT/C offset.