Method and apparatus for processing a photocurrent in both discrete and continuous time

• US 6,741,282 B1
• Filed: 05/05/1998
• Issued: 05/25/2004
• Est. Priority Date: 05/05/1998
• Status: Expired due to Fees

• Current Assignee: Intel Corporation
• Original Assignee: Intel Corporation
• Inventors: Morris, Tonia G.
• Primary Examiner(s): MOE, AUNG SOE
• Application Number:
  US09/072,758
• Time in Patent Office: 2,212 Days
• Field of Search: 348/362, 348/308, 348/300, 348/301, 348/307, 348/309, 348/310, 348/222, 348/302, 348/306, 348/222.1, 250/208.1, 257/291, 257/292, 257/293
• US Class Current: 348/308
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/47 Image sensors with pixel address output; Event-driven image sensors; Selection of pixels to be read out based on image data
• CPC Class Codes: H04N 25/573 the logarithmic type
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

An image sensing array having discrete and continuous time processing capabilities. Integration of a photocurrent is used to produce a high resolution digital image. By also employing continuous time processing of the photocurrent within the image sensing array, the robustness of the imaging system is enhanced. The continuous time processing permits a number of low precision calculations that may be performed within the focal plane or on the edge of the focal plane without the addition of significant circuit complexity. In one embodiment, motion representation is improved through optical flow determination based on the continuous photocurrent. These same determinations may facilitate compression of image data by reducing a search area for moving objects within the image.

Claims

1. An apparatus comprising:

a light sensitive element that generates a photocurrent related to an incident light level;

an integration circuit coupled to the light sensitive element to compute an average of the photocurrent during a sampling period to permit creation of a digital image; and

a continuous time processing circuit coupled to the light sensitive element to receive and process the photocurrent during at least a continuous segment of time, the continuous time processing interpreting an aspect of the digital image.

2. The apparatus of claim 1 wherein the continuous time processing circuit is integrated as part of a focal plane.

3. The apparatus of claim 1 wherein the continuous time processing circuit performs one of:

centroid determination, orientation determination;

temporal derivative calculations;

spatial derivative calculations, optical flow calculations, edge detection;

silicon retina function;

feature detection, and segmentation.

4. The apparatus of claim 1 further comprising:

a current mirror coupled between the light sensitive element and both of the continuous processing circuit and the integration circuit.

5. The apparatus of claim 1 further comprising:

a reset circuit including a current measuring circuit that maintains a constant reset voltage; and

a control switch to control which of the continuous time processing circuit and the integration circuit receives the photocurrent.

6. The apparatus of claim 5 wherein the control switch is activated by a reset signal to direct the photocurrent to the continuous time processing circuit when the reset signal is asserted.

7. The apparatus of claim 5 wherein the current measuring circuit comprises a transconductance amplifier.

8. The apparatus of claim 1 further comprising:

a plurality of additional light sensitive elements subsets of which are coupled together such that an aggregate photocurrent is generated for input into the continuous time processing circuit.

9. The apparatus of claim 1 wherein subsets of pixels are coupled together such that a photocurrent corresponding to each pixel in the subset form an aggregate photocurrent for continuous time processing.

10. The apparatus of claim 9 wherein a subset is one of a row, a column, and a two-dimensional subsection of the surface.

11. The apparatus of claim 9 wherein each pixel comprises a current mirror to copy the photocurrent.

12. A method comprising the steps of:

generating a plurality of photocurrents by exposing a plurality of light sensitive elements to incident light;

integrating the plurality of photocurrents to produce an image corresponding to average light levels at the plurality of light sensitive element during a sampling period; and

performing continuous time processing on the plurality of photocurrents within an image sensing array, the continuous time processing interpreting an aspect of the image.

13. The method of claim 12 further comprising the step of:

copying the plurality of photocurrents to permit concurrent continuous time processing and integration.

14. The method of claim 12 wherein the step of continuous time processing comprises:

accumulating photocurrents of a predefined subset of the light sensitive elements into an aggregate photocurrent.

15. The method of claim 12 wherein the continuous time processing occurs within a focal plane.

16. The method of claim 12 wherein the continuous time processing determines at least one of:

a spatial derivative, a temporal derivative, a photocurrent variance, an object identification, an object centroid, an object orientation, an overall light intensity, and an optical flow.