Sense amplifier having a precision analog reference level for use with image sensors

• US 6,452,152 B1
• Filed: 11/15/2000
• Issued: 09/17/2002
• Est. Priority Date: 02/22/2000
• Status: Expired due to Term

• Current Assignee: Pixim, Inc. (Sony Group Corp.)
• Original Assignee: Pixim, Inc. (Sony Group Corp.)
• Inventors: Yang, David Xiao Dong
• Primary Examiner(s): Allen, Stephone
• Assistant Examiner(s): HILL, BRADFORD K
• Application Number:
  US09/714,350
• Time in Patent Office: 671 Days
• Field of Search: 250/208.1, 250/214.1, 250/214.A, 348/307, 348/308, 348/312, 348/302, 348/311
• US Class Current: 250/208.1
• 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 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array
• CPC Class Codes: H04N 25/772 comprising A/D, V/T, V/F, I/T or I/F converters
• CPC Class Codes: H04N 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

The presently preferred embodiment of the invention comprises a single ended bit-line from each pixel, small swing bit-line detection, a regenerative sense amplifier, and reference generation using precision analog references.

Claims

1. An image sensor, comprising:

a sensor array comprising a plurality of pixels arranged in rows and columns, wherein said sensor array outputs signals on associated bitlines for said pixels, which signals from said pixels collectively represent one or more images of a scene, wherein said sensor array is fabricated in an integrated circuit; and

an individual sense amplifier associated with each bitline for sensing signals from said pixels, said sense amplifier comprising a reference voltage generator for generating an analog reference voltage to compare with a voltage from said pixels on said bitline, wherein said sense amplifier is fabricated in said integrated circuit.

2. The image sensor of claim 1, wherein said reference voltage generator comprises a resistive ladder.

3. The image sensor of claim 2, wherein said resistive ladder comprises two or more resistors stacked in series between two power rails of said integrated circuit.

4. The image sensor of claim 3, wherein said resistors are made of either of polysilicon or are well devices.

5. The image sensor of claim 2, wherein said resistive ladder generates an analog reference voltage as a ratio of two resistors.

6. The image sensor of claim 1, wherein said reference voltage generator comprises a bandgap.

7. The image sensor of claim 1, wherein said analog reference voltage is set at k times the power supply voltage Vdd of said integrated circuit such that said bitline associated with each pixel has a small voltage swing.

8. The image sensor of claim 7, wherein k is 0.9.

9. The image sensor of claim 7, wherein said bitline has a voltage swing of 20 mV or less.

10. In an image sensor, comprising a sensor array comprising a plurality of pixels arranged in rows and columns, wherein said sensor array outputs signals on associated bitlines for said pixels, which signals from said pixels collectively represent one or more images of a scene, wherein said sensor array is fabricated in an integrated circuit;

and an individual sense amplifier associated with each bitline for sensing signals from said pixels, the improvement comprising;

said sense amplifier comprising a reference voltage generator for generating an analog reference voltage to compare with a voltage from said pixels on said bitline, wherein said sense amplifier is fabricated in said integrated circuit.

11. The image sensor of claim 10, wherein said reference voltage generator comprises a resistive ladder.

12. The image sensor of claim 11, wherein said resistive ladder comprises two or more resistors stacked in series between two power rails of said integrated circuit.

13. The image sensor of claim 12, wherein said resistors are made of either of polysilicon or are well devices.

14. The image sensor of claim 11, wherein said resistive ladder generates an analog reference voltages a ratio of two resistors.

15. The image sensor of claim 10, wherein said reference voltage generator comprises a bandgap.

16. The image sensor of claim 10, wherein said analog reference voltage is set at k times the power supply voltage Vdd of said integrated circuit such that said bitline associated with each pixel has a small voltage swing.

17. The image sensor of claim 16, wherein said bitline has a voltage swing of 200 mV or less.

18. A sense amplifier associated with each bitline of an image sensor for sensing signals from pixels in said image sensor, comprising:

a reference voltage generator for generating an analog reference voltage to compare with a voltage from said pixels on said bitline;

wherein said voltage generator comprises a resistive ladder.

19. The sense amplifier of claim 18, wherein said resistive ladder comprises two or more resistors stacked in series between two power rails of said integrated circuit.

20. The sense amplifier of claim 19, wherein said resistors are made of either of polysilicon or are well devices.

21. The sense amplifier of claim 18, wherein said resistive ladder generates an analog reference voltage as a ratio of two resistors.

22. The sense amplifier of claim 18, wherein said analog reference voltage is set at k times the power supply voltage Vdd of said image sensor such that said bitline associated with each pixel has a small voltage swing.

23. The sense amplifier of claim 22, wherein k is 0.9.

24. The image sensor of claim 22, wherein said bitline has a voltage swing of 200 mV or less.

25. A sense amplifier associated with each bitline of an image sensor for sensing signals from pixels in said image sensor, comprising:

a reference voltage generator for generating an analog reference voltage to compare with a voltage from said pixels on said bitline;

wherein said voltage generator comprises a bandgap.

26. The sense amplifier of claim 25, wherein said analog reference voltage is set at k times the power supply voltage Vdd of said image sensor such that said bitline associated with each pixel has a voltage swing of 200 mV or less.

27. A method for sensing a pixel of an image sensor array comprising a plurality of pixels arranged in rows and columns, wherein said sensor array outputs signals on associated bitlines for said pixels, which signals from said pixels collectively represent one or more images of a scene, wherein said sensor array is fabricated in an integrated circuit, the method comprising the steps of:

providing an individual sense amplifier associated with each bitline for sensing signals from said pixels; and

providing in each said sense amplifier a reference voltage generator for generating an analog reference voltage to compare with a voltage from said pixels on said bitline, wherein said sense amplifier is fabricated in said integrated circuit.

28. The method of claim 27, wherein said reference voltage generator comprises a resistive ladder.

29. The method of claim 28, wherein said resistive ladder comprises two or more resistors stacked in series between two power rails of said integrated circuit.

30. The method of claim 29, wherein said resistors are made of either of polysilicon or are well devices.

31. The method of claim 28, wherein said resistive ladder generates an analog reference voltage as a ratio of two resistors.

32. The method of claim 27, wherein said reference voltage generator comprises a bandgap.

33. The method of claim 27, wherein said analog reference voltage is set at k times the power supply voltage Vdd of said integrated circuit such that said bitline associated with each pixel has a voltage swing of 200 mV or less.