CMOS-compatible three-dimensional image sensing using reduced peak energy

• US 6,587,186 B2
• Filed: 06/06/2001
• Issued: 07/01/2003
• Est. Priority Date: 06/06/2000
• 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:
  US09/876,373
• Publication Number:
  US 20010048519A1
• Time in Patent Office: 755 Days
• Field of Search: 356/5-9-, 356/28.5, 356/4.09, 356/4.1
• US Class Current: 356/5.01
• CPC Class Codes: G01C 3/04 Adaptation of rangefinders for combination with telescopes or binoculars
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• 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 7/491 Details of non-pulse systems

Abstract

A three-dimensional time-of-flight (TOF) system includes a low power optical emitter whose idealized output S₁=cos(ω·t) is reflected by a target distance z away as S₂=A·cos(ω·t+Φ), for detection by a two-dimensional array of pixel detectors and associated narrow bandwidth detector electronics and processing circuitry preferably fabricated on a common CMOS IC. Phase shift Φ is proportional to TOF or z, z=Φ·C/2·ω=Φ·C/{2·(2·π·f)}, and A is brightness. Φ, z, and A are determined by homodyne-mixing S₂ with an internally generated phase-delayed version of S₁, whose phase is dynamically forced to match the phase of S₂ by closed-loop feedback. Idealized mixer output per each pixel detector is 0.5·A·{cos(2ω·t+Φ)+cos(Φ)}. On-chip circuitry can use TOE data to simultaneously measure distance, object point velocity, object contours, including user interface with virtual input devices.

Claims

1. A method to determine distance z between a pixel detector and a target, the method comprising the following steps:

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

·

t);

(b) disposing said pixel detector so as to detect an optical energy signal having a high frequency component S₂(ω

·

t)=A·

S₁(ω

·

t−

Φ

) reflected from said target, where A is a coefficient proportional to brightness of said target, and Φ

is phase shift proportional to time-of-flight of light over said distance z; and

(c) homodyne signal-processing said signal S₂(ω

·

t) to generate a phase signal Φ

proportional to said distance z and to preserve said coefficient A;

wherein homodyne signal-processing at step (c) is carried out using an internally generated signal whose frequency is derived from said S₁(ω

·

t) and whose phase is dynamically forced by closed loop feedback to track said high frequency component S₂(ω

·

t).

2. The method of claim 1, wherein at step (a), said high frequency component S₁(ω

·

t) is approximated by S₁(ω

·

t)=cos(ω

·

t).

3. The method of claim 1, wherein:

step (b) includes providing an array of pixel detectors; and

step (c) includes generating said phase signal Φ

for a detected said signal output by each of said pixel detectors.

4. The method of claim 1, wherein step (c) includes homodyne-mixing said signal S₂(ω

·

t) with a signal proportional to S₁(ω

·

t+ψ

),

where ψ

is a variable time delay representing an offset phase angle.

6. The method of claim 4, wherein at steady-state, ψ

=Φ

±

90°

.

7. The method of claim 4, wherein step (c) further includes varying said ψ

to find zero average value for a homodyne product S₁·

S₂.

8. The method of claim 4, wherein step (c) further includes reducing high frequency components in S₁·

S₂ to yield an average value for a homodyne product S₁·

S₂.

9. The method of claim 4, wherein step (c) further includes integrating an average value for said homodyne product S₁·

S₂ to produce said ψ

.

10. The method of claim 1, further including estimating magnitude of said co-efficient A.

11. The method of claim 1, further including a step of estimating magnitude of said co-efficient A by homodyne mixing S₂ with S₁(ω

·

t+ψ

+π

/2),

where ψ

is a variable time delay representing an offset phase angle.

12. The method of claim 4, wherein step (c) includes homodyne-mixing said S₂ with a signal of close frequency that is phase locked onto S₁ to yield an intermediate frequency signal ω

_c, and at least one step selected from a group consisting of (i) homodyne-mixing a resulting intermediate signal again with said ω

_c, and (ii) directly digitizing said intermediate frequency signal ω

_c and extracting Φ

using digital signal processing.

13. The method of claim 1, wherein step (a) includes generating a plurality of discrete frequencies ω

_i selected to reduce aliasing.

14. The method of claim 1, wherein each said step is carried out by circuitry fabricated on a CMOS integrated circuit, said integrated circuit including an array of pixel detectors each identical to said pixel detector.

15. The method of claim 14, wherein said integrated circuit includes a microprocessor, and at least step (c) is executed by said microprocessor.

5. The method of 4, wherein step (c) includes subjecting said input signal S₁(ω

t) to a variable phase delay to generate said S₁(ω

·

t+ψ

).

16. A CMOS-implementable integrated circuit (IC) time of flight (TOE) measurement system used with an optical emitter to determine distance z between said IC and a target, the IC including:

a generator coupleable to said optical emitter to cause said optical emitter to output a signal having a high frequency component S₁(ω

·

t);

an array of pixel detectors to detect an optical energy signal having a high frequency component representable as S_2i(ω

·

t)=A_i·

S₁(ω

·

t−

Φ

) reflected from said target, where i is an integer representing an i-th one of said pixel detectors, A_i is a coefficient proportional to brightness of said target as perceived by the i-th one of said pixel detectors, and Φ

, is phase shift proportional to time-of-flight of light over said distance z;

for each of said pixel detectors, an associated electronic circuit coupled to receive and homodyne signal-process said signal S_2i(Φ

·

t) and to generate a phase signal Φ

_i proportional to said distance z and to preserve said coefficient A_i;

wherein homodyne signal-processing is carried out using a signal, internally generated by said circuit, whose frequency is derived from said S₁(ω

·

t) and whose phase is dynamically forced by closed loop feedback to track said high frequency component S₂(ω

·

t).

17. The IC of claim 16, wherein said high frequency component S₁(ω

·

t) is approximated by S₁(ω

·

t)=cos(ω

·

t).

18. The IC of claim 16, wherein said electronic circuit signal processes by homodyne-mixing said signal S_2i(ω

·

t) with a signal proportional to S₁(ω

·

t+ψ

_i), where ω

_i is a variable time delay representing an offset phase angle that at steady-state is Φ

_i±

90°

.

19. The IC of claim 18, wherein said electronic circuit signal processes by subjecting said signal S₁(ω

t) to a variable phase delay to generate said S₁(ω

·

t+ψ

).

20. The IC of claim 18, wherein said electronic circuit further signal processes by carrying out at least one function selecting from a group consisting of (a) varying said ψ

_i to find zero average value for a homodyne product S₁·

S_2i, (b) reducing high frequency components in S₁·

S_2i to yield an average value for a homodyne product S₁·

S_2i, (c) integrating an average value for said homodyne product S₁·

S_2i to produce said ψ

_i, and (d) estimating magnitude of said co-efficient A_i.