Selective analog-to-digital conversion for a digital pixel sensor

• US 6,498,576 B1
• Filed: 03/30/2001
• Issued: 12/24/2002
• Est. Priority Date: 05/09/2000
• Status: Expired due to Term

• Current Assignee: Pixim, Inc. (Sony Group Corp.)
• Original Assignee: Pixim, Inc. (Sony Group Corp.)
• Inventors: Tian, Hui, Yang, David Xiao Dong
• Primary Examiner(s): Wamsley, Patrick
• Assistant Examiner(s): Mai, Lam T.
• Application Number:
  US09/823,344
• Time in Patent Office: 634 Days
• Field of Search: 341/155, 341/156, 341/160
• US Class Current: 341/155
• CPC Class Codes: H04N 1/00307 with a mobile telephone apparatus constructional features of portable telephone sets H04M1/0202; mobile radio systems H04W84/00
• CPC Class Codes: H04N 2201/0068 Converting from still picture data
• CPC Class Codes: H04N 23/70 Circuitry for compensating brightness variation in the scene
• CPC Class Codes: H04N 23/741 by increasing the dynamic range of the image compared to the dynamic range of the electronic image sensors
• CPC Class Codes: H04N 25/00 Circuitry of solid-state image sensors [SSIS]; Control thereof
• CPC Class Codes: H04N 25/76 Addressed sensors, e.g. MOS or CMOS sensors
• CPC Class Codes: H04N 25/772 comprising A/D, V/T, V/F, I/T or I/F converters
• CPC Class Codes: H04N 7/142 Constructional details of the terminal equipment, e.g. arrangements of the camera and the display

Abstract

A system and method for performing low-power analog-to-digital conversion in digital imaging system utilizing a time-indexed multiple sampling technique is presented. The analog-to-digital converter is switched off when the digital image signal resulting from an exposure time selected from a plurality of exposure times satisfies a threshold value.

Claims

1. A method of analog-to-digital conversion for a pixel sensor configured to produce an analog signal for each of a plurality of exposure times within a frame, the pixel sensor being coupled to an analog-to-digital converter for converting the analog signals into digital signals, the method comprising:

determining whether the analog signals resulting from exposure times subsequent to a given exposure time should be converted; and

if the determining step indicates the analog signals resulting from exposure times subsequent to the given exposure time should not be converted, disabling the analog-to-digital converter from converting these analog signals.

2. The method of claim 1, wherein the determining step tests whether the analog signal resulting from the given exposure time exceeds a threshold.

3. The method of claim 2, further comprising:

setting a binary flag if the testing indicates the analog image signal resulting from the given exposure time exceeds the threshold value.

4. The method of claim 3, wherein the analog-to-digital converter comprises a one-bit comparator, and wherein the disabling step comprises switching off the one-bit comparator in response to the state of the binary flag.

5. The method of claim 4, wherein the one-bit comparator has a DC path to ground including a switch and the one-bit comparator is switched off by turning off the switch.

6. The method of claim 4, wherein the one-bit comparator has a DC path to a power supply including a switch and the one-bit comparator is switched off by turning off the switch.

7. The method of claim 6, wherein the switch is a PMOS transistor having a gate coupled to receive the binary flag, the binary flag being in a high voltage state when the threshold value is exceeded.

8. A pixel sensor system, comprising:

a pixel sensor configured to producing an analog image signal for each of a plurality of exposure times during a frame, and

an analog-to-digital converter for converting the analog signals into corresponding digital signals, the analog-to-digital converter having a switch for switching the analog-to-digital converter on and off,

wherein the pixel sensor system is configured to test, after each exposure time, the resulting analog signal against a threshold value, the pixel sensor system switching off the analog-to-digital converter'"'"'s switch if the threshold value is exceeded.

9. The pixel sensor system of claim 8, wherein the pixel sensor system is further configured to set a binary flag if the threshold value is exceeded during a frame, the analog-to-digital converter'"'"'s switch being responsive to the binary flag.

10. The pixel sensor system of claim 9, wherein the analog-to-digital converter includes a one-bit comparator having a DC path to ground, the DC path including the switch.

11. The pixel sensor system of claim 10, wherein the switch is a NMOS transistor, the binary flag being set to a low voltage state when the threshold value is satisfied.

12. The pixel sensor system of claim 9, wherein the analog-to-digital converter includes a one-bit comparator having a DC path to a power supply, the DC path including the switch.

13. The pixel sensor system of claim 12, wherein the witch is a PMOS transistor, the binary flag being set to a high voltage state when the threshold value is satisfied.

14. The pixel sensor system of claim 8, wherein the plurality of exposure times comprises integer multiples of a period T.

15. The pixel sensor system of claim 14, wherein the plurality of exposure times comprises T, 2T, 4T, and 8T.

16. The pixel sensor system of claim 8, wherein the threshold value is chosen such that the corresponding digital image signal exceeding the threshold is substantially saturated.

17. A method of analog-to-digital conversion for an array of pixel sensors, each pixel sensor being configured to produce an analog signal for each of a plurality of exposure times within a frame, each pixel sensor being coupled to its own analog-to-digital converter for converting the analog signals into digital signals;

the method comprising;

after each exposure time;

determining which pixel sensors whose analog signal will be converted and which pixel sensors whose analog signal will not converted;

converting the analog signals from those pixel sensors as determined in the determining step, and

for those pixel sensors whose analog signals will not be converted, disabling the analog-to-digital converters for these pixel sensors from converting their analog signals.