Method and system to enhance timing accuracy for time-of-flight systems

• US 7,636,150 B1
• Filed: 11/30/2007
• Issued: 12/22/2009
• Est. Priority Date: 12/01/2006
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Canesta Incorporated (Microsoft Corporation)
• Inventors: McCauley, Richard J., Snow, Dana R.
• Primary Examiner(s): Tarcza; Thomas H
• Assistant Examiner(s): Ratcliffe; Luke D
• Application Number:
  US11/998,713
• Time in Patent Office: 753 Days
• Field of Search: 356 301- 22
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4863 Detector arrays, e.g. charge-transfer gates
• CPC Class Codes: G01S 7/497 Means for monitoring or calibrating

Abstract

A method and system to enhance accuracy of measurement of distance Z in a TOF system dynamically provides tight control over the phase and/or timing relationship of clock pulses used in the TOF system. Enhanced frequency control is imposed over a high speed oscillator whose output(s) control a timing generator, whose outputs are coupled to circuitry associated with the detection array in the TOF system, and with the TOF clock timing circuitry. The timing generator is coupled to a delay locked loop (DLL) and/or phase lock loop (PLL), which loop(s) are feedback coupled to the waveform circuit that drives the source of electromagnetic energy emitted by the TOF system.

Claims

1. For use with a time-of-flight (TOF) imaging system that includes an optical energy emitter unit, and an array of optical detectors operable synchronously relative to signals from a TOF system clock governing operation of said optical energy emitter unit, said array detecting at least a fraction of emitted optical energy reflected by a target object, and further includes means for determining distance Z to the target object from detected reflected optical energy, an enhanced measurement system that improves measurement accuracy of said TOF system comprising:

a timing generator that generates at least one clock signal whose average clock frequency is controlled to better than about ±

1% of nominal frequency, said timing generator coupled to said TOF system clock; and

a feedback mechanism, operable absent coupling to said array of optical detectors, coupled to said timing generator and responsive to a signal representative of optical energy from said optical energy emitter unit;

wherein at least one temporal characteristic of optical energy emitted by said optical energy emitter unit is more precisely controlled than if said TOF imaging system operated without said enhanced measurement system.

2. The enhanced measurement system of claim 1, wherein said TOF imaging system determines said distance Z using at least one of (i) knowledge of when in time said optical energy emitter unit begins to emit optical energy, (ii) knowledge of when in time said optical energy emitter unit ceases to emit optical energy, and (iii) relative shift in phase between emitted optical energy and reflected detected optical energy.

3. The enhanced measurement system of claim 1, wherein said timing generator includes at least one of (i) an oscillator operable over a frequency range of at least about 0.5 GHz to about 1.0 GHz coupled to said timing generator, (ii) an oscillator operable over a frequency range of at least about 0.5 GHz to about 1.0 GHz and input to said timing generator, and (iii) an oscillator operable over a frequency range of at least about 0.5 GHz to about 1.0 GHz embedded within said timing generator.

4. The enhanced measurement system of claim 1, wherein frequency control is implemented using at least one of (i) a digital hardware closed loop, (ii) a software controlled loop (SCCL) unit, and (iii) a phase lock loop (PLL) unit.

5. The enhanced measurement system of claim 1, wherein, relative to a reference clock, a clock signal generated by said timing generator has a clock signal phase and a clock signal width that are controllable independently of each other.

6. The enhanced measurement system of claim 1, wherein said feedback mechanism includes at least one of (i) a digital delay line loop (DLL) unit, (ii) a phase lock loop (PLL) unit, and (iii) a software controlled closed loop (SCCL) unit.

7. The enhanced measurement system of claim 1, wherein at least one temporal characteristic of emitted optical energy emitted by said optical energy emitter unit is controlled and selected from a group consisting of (i) zero-to-active state transition time of emitted said optical energy, (ii) active state-to-zero transition time of emitted said optical energy, and (iii) phase shift of emitted said optical energy relative to phase shift of a signal controlled said timing generator.

8. The enhanced measurement system of claim 1, further including means for optical energy sensing, coupled to said optical energy emitter unit, to sense actual emitted optical energy.

9. The enhanced measurement system of claim 1, wherein said timing generator controls at least one characteristic of an optical energy waveform emitted by said TOF system, said characteristic selected from a group consisting of (i) shape of rise time, (ii) shape of fall time, (iii) effective pulse width, (iv) initial offset phase, and (e) repetition frequency.

10. For use with a time-of-flight (TOF) imaging system that includes an optical energy emitter unit, and an array of optical detectors operable synchronously relative to signals from a TOF system clock governing operation of said optical energy emitter unit, said array detecting at least a fraction of emitted said optical energy reflected by a target object, and further includes means for determining distance Z to the target object from detected reflected optical energy, a method to enhance accuracy of measurements made by said TOF imaging system, the method comprising the following steps:

(a) providing a timing generator generating at least one clock signal whose average clock frequency is controlled to better than about ±

1% of nominal frequency, which clock signal is coupled to said TOF system clock; and

(b) employing feedback, operable absent coupling to said array of optical detectors, coupled between said timing generator, which feedback is responsive, to a signal representative of optical energy from said optical energy emitter unit;

wherein at least one temporal characteristic of optical energy emitted by said optical energy emitter unit is more precisely controlled than if said TOF imaging system operated without carrying out the method of step (a) and step (b).

11. The method of claim 10, wherein said TOF imaging system determines said distance Z using at least one of (i) knowledge of when in time said optical energy emitter unit begins to emit optical energy, (ii) knowledge of when in time said optical energy emitter unit ceases to emit optical energy, and (iii) relative shift in phase between emitted optical energy and reflected detected optical energy.

12. The method of claim 10, wherein said timing generator provided at step (a) includes at least one of (i) an oscillator operable over a frequency range of at least about 0.5 GHz to about 1.0 GHz coupled to said timing generator, (ii) an oscillator operable over a frequency range of at least about 0.5 GHz to about 1.0 GHz and input to said timing generator, and (iii) an oscillator operable over a frequency range of at least about 0.5 GHz to about 1.0 GHz embedded within said timing generator.

13. The method of claim 10, wherein frequency control is implemented using at least one of (i) a digital hardware closed loop, (ii) a software controlled loop (SCCL) unit, and (iii) a phase lock loop (PLL) unit.

14. The method of claim 10, wherein, relative to a reference clock, a clock signal generated by said timing generator has a clock signal phase and a clock signal width that are controllable independently of each other.

15. The method of claim 10, wherein step (b) includes at least one of (i) a digital delay line loop (DLL) unit, (ii) a phase lock loop (PLL) unit, and (iii) a software controlled closed loop (SCCL) unit.

16. The method of claim 10, wherein at least one temporal characteristic of emitted optical energy from said optical energy emitter unit is controlled and selected from a group consisting of (i) zero-to-active state transition time of emitted said optical energy, (ii) active state-to-zero transition time of emitted said optical energy, and (iii) phase shift of emitted said optical energy relative to phase shift of a signal controlled said timing generator.

17. The method of claim 10, further including coupling means for optical energy sensing to said optical energy emitter unit to sense actual emitted optical energy.

18. The method of claim 10, wherein said timing generator provided at step (a) controls at least one characteristic of an optical energy waveform emitted by said TOF system, said characteristic selected from a group consisting of (i) shape of rise time, (ii) shape of fall time, (iii) effective pulse width, (iv) initial offset phase, and (e) repetition frequency.

19. For use with a time-of-flight (TOF) imaging system that includes an optical energy emitter unit, and an array of optical detectors operable synchronously relative to signals from a TOF system clock governing operation of said optical energy emitter unit, said array detecting at least a fraction of emitted said optical energy reflected by a target object, and further includes means for determining from detected reflected optical energy distance Z to the target object, a method to enhance accuracy of measurements made by said TOF imaging system, the method comprising the following steps:

(a) providing a frequency controller outputting at least one oscillator frequency control signal whose average clock frequency is controlled to better than about ±

1% of nominal frequency;

(b) providing an oscillator operating at a frequency higher than said TOF system clock, coupled to said frequency controller, and having at least one output frequency controlled by said oscillator frequency control signal;

(c) providing a timing generator, coupled to receive at least one output from said oscillator, generating at least one clock signal coupled to said TOF system clock;

(d) coupling a feedback mechanism to said timing generator and responsive to optical energy sensed directly at said optical energy emitter; and

(e) coupling an emission source unit to an output from said feedback mechanism and to an input of said optical energy emitter;

wherein at least one temporal characteristic of optical energy emitted by said optical energy emitter is more precisely controlled than if said TOF system operated without said time measurement method.

20. The method of claim 19, wherein said feedback mechanism includes at least one of (i) a digital delay line loop (DLL) unit, (ii) a phase lock loop (PLL) unit, and (iii) a software controlled closed loop (SCCL) unit.