Demodulation sensor with separate pixel and storage arrays

Patent metadata

Field	Value
Publication number	US-9442196-B2
Application number	US-98573711-A
Country	US
Kind code	B2
Filing date	Jan 6, 2011
Priority date	Jan 6, 2010
Publication date	Sep 13, 2016
Grant date	Sep 13, 2016

Abstract

A demodulation image sensor, such as used in time of flight (TOF) cameras, extracts all storage- and post-processing-related steps from the pixels to another array of storage and processing elements (proxels) on the chip. The pixel array has the task of photo-detection, first processing and intermediate storage, while the array of storage and processing elements provides further processing and enhanced storage capabilities for each pixel individually. The architecture can be used to address problems due to the down-scaling of the pixel size. Typically, either the photo-sensitivity or the signal storage capacitance suffers significantly. Both a lower sensitivity and smaller storage capacitances have negative influence on the image quality. The disclosed architecture allows for keeping the storage capacitance unaffected by the pixel down-scaling. In addition to that, it provides a high degree of flexibility in integrating more intelligence into the image sensor design already on the level of the pixel array. In particular, if applied to demodulation pixels, the flexibility of the architecture allows for integrating on sensor-level concepts for multi-tap sampling, mismatch compensation, background suppression and so on, without any requirement to adjust the particular demodulation pixel architecture.

First claim

What is claimed is:

1. A demodulation sensor implemented on a chip, comprising:
a pixel array comprising pixels each of which produces at least two samples of a scene, which is illuminated by modulated light from a light emitter;
a proxel array on the chip, the proxel array being physically separated from the pixel array and comprising storage elements and processing elements, each of the storage elements operable to receive the at least two samples from a corresponding one of the pixels; and
a transfer system to transfer the samples from the pixel array to the corresponding storage elements of the proxel array;
wherein the proxel array is arranged to alternate storage of the at least two samples between two different storage elements to perform in-pixel mismatch cancellation, and wherein each storage element is arranged to accumulate a plurality of phase-delay-matching sub-images for a single image.

2. A demodulation sensor as claimed in claim 1 , wherein the pixels comprise:
photosensitive regions in which incoming light generates charge carriers, and demodulators/correlators that transfer the charge carriers among multiple storage sites.

3. A demodulation sensor as claimed in claim 1 , wherein the processing elements monitor storage elements that receive the samples for saturation.

4. A demodulation sensor as claimed in claim 3 , wherein a voltage of one or more of the storage elements is continuously monitored by a comparator to determine whether the voltage has reached a predetermined saturation indicating reference voltage.

5. A demodulation sensor as claimed in claim 1 , further comprising a post processing unit for determining depth information.

6. A demodulation method, comprising:
detecting modulated light in a pixel array, which is implemented on a chip, the pixel array comprising pixels each of which produces at least two samples of the modulated light with the modulation of a light emitter;
transferring the samples from each of the pixels to a proxel array on the chip, the proxel array being physically separated from the pixel array and comprising storage elements and processing elements; and
receiving the at least two samples in storage elements of the proxel array from a corresponding one of the pixels, wherein individual ones of the storage elements accumulate signals for a plurality of phase-delay-matching sub-images corresponding to a single image.

7. The demodulation sensor of claim 1 wherein the at least two samples are acquired per period of modulating light generated by a light source.

8. The demodulation sensor of claim 1 wherein each proxel in the proxel array is associated with a particular pixel in the pixel array.

9. A demodulation sensor as claimed in claim 1 , wherein each storage element is arranged to accumulate a two phase-delay-matching sub-images for a single image.

10. A demodulation sensor as claimed in claim 1 , wherein each storage element is arranged to accumulate a four phase-delay-matching sub-images for a single image.

11. A demodulation sensor as claimed in claim 1 , wherein the storage elements include capacitive storage sites.

12. A demodulation sensor as claimed in claim 1 wherein the proxel array comprises a first group of storage elements operable to accumulate photogenerated charge for a first one of the samples and a second group of storage elements operable to accumulate photogenerated charge for a second one of the samples, wherein, for each of the first and second groups of storage elements, if an amount of charge stored on a first one of the storage elements in the group exceeds a predetermined amount, overflow charge is stored on a second one of the storage elements in the same group.

13. A demodulation sensor as claimed in claim 12 , wherein each of the first and second groups of storage elements comprises a plurality of capacitive storage sites.

14. A demodulation sensor as claimed in claim 13 , wherein, for each of the first and second groups of storage elements, if a voltage across a first one of the capacitive storage sites in the particular group exceeds a first amount, overflow charge is accumulated by a second one of the capacitive storage sites in the same group, and if a voltage across a second one of the capacitive storage sites in the particular group exceeds a second amount, overflow charge is accumulated by a third one of the capacitive storage sites in the same group.

15. A demodulation sensor as claimed in claim 14 , wherein the first, second and third capacitive storage sites in a particular one of the first or second groups is operable to accumulate a different amount of photogenerated charge from one another.

16. A demodulation sensor as claimed in claim 1 wherein the transfer system comprises analog-to digital conversion circuitry that converts the samples from analog to digital so that the samples received for processing by the proxel array are digital.

17. The demodulation method of claim 6 including:
converting the at least two samples of each of the pixels from analog signals to digital signals; and
transferring the digital signals for each of the pixels to the proxel array.

Assignees

• Buettgen Bernhard
• Oggier Thierry
• Heptagon Micro Optics Pte Ltd

Inventors

• Buettgen Bernhard
• Oggier Thierry

Classifications

• G01S7/4914 Primary

  of detector arrays, e.g. charge-transfer gates · CPC title

• G01S7/4918 Primary

  Controlling received signal intensity, gain or exposure of sensor · CPC title

• G01S17/36

  with phase comparison between the received signal and the contemporaneously transmitted signal · CPC title

• G01S17/894

  Three-dimensional [3D] imaging with simultaneous measurement of time-of-flight at a two-dimensional [2D] array of receiver pixels, e.g. time-of-flight cameras or flash lidar · CPC title

• G01S17/89 Primary

  for mapping or imaging · CPC title