Method and system to enhance dynamic range conversion useable with CMOS three-dimensional imaging

• US 20020176067A1
• Filed: 05/23/2002
• Published: 11/28/2002
• Est. Priority Date: 05/23/2001
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Canesta Incorporated (Microsoft Corporation)
• Inventors: Charbon, Edoardo
• Granted Patent: US 6,678,039 B2
• Time in Patent Office: Days
• US Class Current: 356/4.01
• CPC Class Codes: G01S 17/08 for measuring distance only indirect measurement G01S17/46; active triangulation systems G01S17/48
• CPC Class Codes: G01S 17/894 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 7/4863 Detector arrays, e.g. charge-transfer gates
• CPC Class Codes: G01S 7/4868 Controlling received signal intensity or exposure of sensor
• CPC Class Codes: G01S 7/487 Extracting wanted echo signals , e.g. pulse detection
• CPC Class Codes: H04N 23/76 by influencing the image signals
• CPC Class Codes: H04N 25/57 Control of the dynamic range
• CPC Class Codes: H04N 25/65 applied to reset noise, e.g. KTC noise related to CMOS structures by techniques other than CDS

Abstract

High dynamic range brightness information is acquired by inputting detection current to a high (adjustable) gain resettable integrator whose output V(t) is compared to a Vth threshold by a comparator whose output is counted by a reset counter as V(t)≧Vth. When a desired count is attained, data acquisition ends, the counter is read, and the entire circuit is reset. A TOF data acquisition circuit includes first and second sequences of series-coupled delay units, and a like number of latch units coupled between respective delay units. A phase discriminator compares output from each chain and feedback a signal to one of the chains and to a comparator and can equalize delay through each chain. A control voltage is coupled to the remaining chain to affect through-propagation delay time. The latch units can capture the precise time when V(t)≧Vth. Successive measurement approximation can enhance TOF resolution.

Claims

1. A high dynamic range circuit useable with a range finding system that detects reflected energy to determine time-of-flight to a target object reflecting said energy, the circuit comprising:

at least one detector to detect reflected said energy and to output a detection signal;

for each said detector, a resettable integrator coupled to integrate said detection signal and output an integration signal, said resettable integrator having a gain G that is dynamically variable;

for each said detector, a comparator coupled to receive and to compare said integration signal against a threshold level and to output a pulse when said integration signal exceeds said threshold level, an output of said comparator fed-back to reset said detector; and

for each said detector, a resettable logic counter coupled to count each said pulse output by said comparator;

means for providing a RESET signal to said integrator and to said logic counter;

wherein when said resettable logic counter attains a given count, a count value within said logic counter is readout, and said RESET signal is provided to reset at least two of said detector, said comparator, and said logic counter.

2. The circuit of claim 1, wherein said system is a three-dimensional range finding system, and wherein said detector is a photodiode.

3. The circuit of claim 1, wherein said detector is a photodiode, and said resettable integrator is a capacitor selected from a group consisting of (a) a parasitic shunt capacitance of said photodiode, and (b) a physical capacitor.

4. The circuit of claim 1, wherein said detector is a photodiode coupled to a bias source, and an output of said comparator is fed-back to said bias source to reset said photodiode.

5. The circuit of claim 1, wherein said logic counter is implemented using a circuit selected from a group consisting of (a) a series-coupled group of latch circuits, (b) an asynchronous ripple counter, (c) a synchronous counter, and (d) a pseudo-random generator counter.

6. The circuit of claim 1, wherein:

said detector is a photodiode in an array of photodiodes;

one said circuit is provided for each said photodiode; and

said array and each said circuit are fabricated on a single integrated circuit.

7. The circuit of claim 1, wherein:

said detector is a photodiode in an array of photodiodes;

one said circuit is multiplex-provided for at least two of said photodiode; and

said array and each said circuit are fabricated on a single integrated circuit.

8. A method to enhance dynamic range of brightness data acquired by a range finding system that emits energy and employs at least one detector to detect target object reflected said energy and to output a detection signal for use in determining time-of-flight to said target object, the method including the following steps:

(a) providing for each said detector a resettable integrator having dynamically variable gain that is coupled to integrate said detection signal and to output an integration signal;

(b) providing for each said detector a comparator coupled to receive and to compare said integration signal against a threshold level and to output a pulse when said integration signal exceeds said threshold level, an output of said comparator being fed-back to said detector;

(c) for each said detector, providing a resettable logic counter coupled to count each said pulse output by said comparator;

(d) reading out a count value from said logic counter when said logic counter attains a given count; and

(e) resetting at least two of said detector, said integrator, and said logic counter.

9. The method of claim 8, wherein step (a) includes providing a capacitor for use as said resettable integrator.

10. The method of claim 8, wherein:

said detector is a photodiode coupled to a bias device;

further including;

feeding back an output of said comparator to said bias device.

11. The method of claim 8, wherein:

said system is a three-dimensional time-of-flight range finding system; and

said detector is a photodiode.

13. The circuit of claim 12, wherein at least one of said first means for propagating and said second means for propagating includes a series-coupled of delay elements, each delay element contributing a known time delay.

14. The circuit of claim 12, wherein at least one of said first means for propagating and said second means for propagating includes a series-coupled of delay elements, each delay element contributing a common time delay.

15. The circuit of claim 12, further including:

means for calibrating said circuit such that propagation time through said first means for propagating is made substantially but not precisely equal to propagation time through said second means for propagating.

16. The circuit of claim 12, wherein:

said first means for propagating includes a number N of series-coupled delay elements, where N is an integer greater than one;

said second means for propagating includes N series-coupled delay elements;

said means for determining includes N latch units;

each of said latch units having a clock input coupled to an output of an associated one of said delay elements in said first means for propagating, and having a data input coupled to an input of an associated one of said delay elements in said second means for propagating;

wherein coincidence is determined by identifying a state change for each of said latch units.

17. The circuit of claim 16, further including:

a phase discriminator having a first input coupled to receive an output propagated through said first means for propagation, and having a second input coupled to receive an output propagated through said second means for propagation, and having an output coupled to vary time delay through said delay elements in said first means for propagation;

wherein in a calibration mode, propagation time through said first means for propagating is made substantially but not precisely equal to propagation time through said second means for propagating.

18. The circuit of claim 16, further including:

means for varying time delay through each of said delay elements.

20. The circuit of claim 19, further including means for calibrating said circuit such that propagation time through said first means for propagating is made substantially but not precisely equal to propagation time through said second means for propagating.

21. The circuit of claim 19, wherein said circuit is fabricated on a common integrated circuit with at least some of said range finding system.

12. A circuit to resolve time-of flight (TOF) useable with a three-dimensional range finding system that emits energy and detects reflected said energy to determine TOF to a target object reflecting said energy, the circuit comprising:

first means for propagating a copy of emitted said energy;

second means for propagating a copy of detected reflected said energy; and

means for determining when in time the propagated copy of emitted said energy coincides with the propagated copy of detected reflected said energy;

wherein a time interval within said means for determining at which coincidence is determined is used to resolve said TOF.

19. A circuit to resolve time-of flight (TOF) useable with a three-dimensional range finding system that emits energy and detects reflected said energy to determine TOF to a target object reflecting said energy, the circuit comprising:

a first series-coupled group of N delay elements through which a copy of emitted said energy is propagated, where N is an integer greater than one;

a second series-coupled group of N delay elements through which a copy of detected said energy is propagated;

second means for propagating a copy of detected reflected said energy; and

a series-coupled group of N latch elements, each of said elements having a first input coupled to an input of an associated one of said first series-coupled group of N delay elements, and having a second input coupled to an output of one of said second series-coupled group of N delay elements;

a phase discriminator coupled to receive an output from said first and from said second series-coupled group of N delay elements, and generating an output signal therefrom that is coupled to vary delay through said first series-coupled group of N delay elements;

wherein a time interval within said N latch elements at which coincidence is determined is used to resolve said TOF.

22. A method to resolve time-of flight (TOF) useable with a three-dimensional range finding system that emits energy and detects reflected said energy to determine TOF to a target object reflecting said energy, the method including the following steps:

(a) propagating a copy of emitted said energy through a first delay system that permits observing incrementally delayed versions of the propagated said copy;

(b) propagating a copy of detected reflected said energy through a second delay system that permits observing incrementally delayed version of the propagated said copy;

(c) comparing signals incrementally delayed through said first delay system with signals incrementally delayed through said second delay system to determine closest coincidence of propagated said signals;

wherein determination of closest said coincidence is used to resolve said TOF.

23. The method of claim 22, further including applying successive approximation to enhance resolution of said TOF.

24. The method of claim 22, further including, in a calibration mode, inputting an output from said first delay system and from said second delay system to a phase discriminator whose output is fed-back to control delay through said first delay system.

25. The method of claim 22, further including, in a calibration mode, forcing substantial but not perfect equalization of total delay through said first delay system with total delay through said second delay system;

wherein TOF resolution is approximated by differential total delay through said first delay system and said second delay system.

26. The method of claim 25, further including repeatingsaid calibration mode such that substantial but not perfect equalization of total delay is achieved for a different time region that is a subset of a time region in which a previous said calibration mode was carried out;

wherein successive approximation enhances resolution of said TOF.

28. The IC of claim 27, further including:

means for uniquely identifying a pattern of energy emitted by said generator; and

means for enabling said photodiode detectors to discern reflected energy emitted by said generator from energy emitted by other generators.

29. The IC of claim 28, wherein:

said generator emits energy in a pattern governed by a sub-system selected from a group consisting of (a) an amplitude modulation pattern, (b) a frequency modulation pattern, (c) a phase-amplitude modulated pattern, (d) a pulse phase modulation pattern, (e) a phase shift keying pattern, and (f) a pulse position modulation pattern.

30. The IC of claim 29, further including:

means enabling said photodiode detectors to recognized a pattern of energy emitted by said generator, said pattern selected from a group consisting of (a) amplitude demodulation, (b) frequency demodulation, (c) phase-amplitude demodulation, (d) pulse phase demodulation, (e) a phase shift de-keying, and (f) pulse position demodulation.

27. A CMOS-implementable integrated circuit (IC) time-of-flight (TOF) measurement system used with a generator emitting energy a portion of which is reflected by a target object a distance Z from said IC, the IC comprising:

for each of said photodiode detectors, at least one of a first circuit and a second circuit;

said first circuit comprising;

a resettable integrator coupled to integrate a detection signal output by the photodiode detector, said resettable integrator having a dynamically variable gain G;

a comparator coupled to receive and to compare an integration signal output by said integrator against a threshold level and to output a pulse when said integration signal exceeds said threshold level, an output of said comparator fed-back to reset said photodiode detector; and

a resettable logic counter coupled to count each said pulse output by said comparator;

means for providing a RESET signal to said integrator and to said logic counter;

wherein when said resettable logic counter attains a given count, a count value within said logic counter is readout, and said RESET signal is provided to reset at least two of said detector, said comparator, and said logic counter;

said second circuit comprising;

first means for propagating a copy of emitted said energy;

second means for propagating a copy of detected reflected said energy; and

means for determining when in time the propagated copy of emitted said energy coincides with the propagated copy of detected reflected said energy;

wherein a time interval within said means for determining at which coincidence is determined is used to resolve said TOF.