Increasing readout speed in CMOS aps sensors through block readout

• US 8,054,361 B2
• Filed: 09/25/2009
• Issued: 11/08/2011
• Est. Priority Date: 03/23/1998
• Status: Expired due to Fees

• Current Assignee: Round Rock Research LLC
• Original Assignee: Round Rock Research LLC
• Inventors: Ang, Lin-Ping
• Primary Examiner(s): Ometz; David L
• Assistant Examiner(s): Spinks; Antoinette T
• Application Number:
  US12/566,814
• Publication Number:
  US 20100103301A1
• Time in Patent Office: 774 Days
• Field of Search: 348/308, 348/302, 348/304, 348/307, 348/241, 348/248, 348/294, 250/208.1
• US Class Current: 348/308
• CPC Class Codes: H04N 25/70 SSIS architectures; Circuits associated therewith
• CPC Class Codes: H04N 25/75 Circuitry for providing, modifying or processing image signals from the pixel array

Abstract

A method and associated architecture for dividing column readout circuitry in an active pixel sensor in a manner which reduces the parasitic capacitance on the readout line. In a preferred implementation, column readout circuits are grouped in blocks and provided with block signaling. Accordingly, only column output circuits in a selected block significantly impart a parasitic capacitance effect on shared column readout lines. Block signaling allows increasing pixel readout rate while maintaining a constant frame rate for utility in large format high-speed imaging applications.

Claims

1. An image sensor, comprising:

a pixel array comprising a plurality of pixels, organized into N selectable rows and M columns, wherein N and M are positive integers;

M column output circuits, each of which can be actively coupled to pixels in the N rows in a respective column, each of said M column output circuits for respectively outputting a respective signal corresponding to a respective pixel of a selected row, said M column output circuits being organized into B blocks, B being a positive integer greater than 1, each of said B blocks comprising k of said M column output circuits, wherein k is a positive integer greater than 1 and k=M/B;

B block output lines each for receiving signals from said k column output circuits of a respective block; and

selection circuitry between said B block output lines and a master output line for actively coupling a single one of said B block output lines to said master output line at a time and thereby allow said k column output circuits associated with an actively coupled block output line to be actively coupled to said master output line through said selection circuitry.

2. The image sensor of claim 1, wherein in each block, said k column output circuits are associated with consecutive pixels in said selected row, k is greater than two, and B is greater than two.

3. An image sensor, comprising:

a pixel array comprising a plurality of pixels, organized into N rows and M columns, wherein N and M are positive integers;

M output circuits, each of said M output circuits for respectively outputting a respective signal associated with a respective one of M pixels of a selected row, wherein said M output circuits are organized into B blocks, B being a positive integer greater than two, each of said B blocks comprising k of said M output circuits, wherein k is a positive integer such that k=M/B;

B block output lines each coupled to said k output circuits of a respective block;

a master output line; and

a selection circuit, for actively coupling a single one of said B block output lines to said master output line at a time.

4. The image sensor of claim 3, wherein M is at least 1024 and k is at least 32.

5. The image sensor of claim 3, wherein said image sensor is configured to control said selection circuit to sequentially select each of said B blocks by actively coupling a respective one of said block output lines of a respective selected block to said master output line.

6. The image sensor of claim 5, wherein said image sensor is further configured to sequentially cause each of said k output circuits of said respective selected block to be actively coupled to said master output line via said respective one of said block output lines of said respective selected block.

7. The image sensor of claim 3, wherein said selection circuit comprises:

B switches, each of said B switches respectively associated with one of said B blocks to couple a respective one of the B block output lines with the master output line.

8. The image sensor of claim 7, wherein each of said B switches is a respective N-channel transistor having one source/drain connected to a respective one of said B block output lines of an associated one of said B blocks and another source/drain connected to the master output line.

9. The imager of claim 8, wherein in each block, said k column output circuits are associated with consecutive pixels in said selected row.

10. A CMOS imager, comprising:

a pixel array comprising a plurality of pixels, organized into N rows and M columns, wherein N and M are positive integers;

M column output circuits, each of which can be actively coupled to the N rows in a column, each of said M output circuits to output a respective signal associated with a respective pixel of a selected row, wherein said M column output circuits are organized into B blocks, B being a positive integer greater than two, each of said B blocks comprising k of said M column output circuits, wherein k is a positive integer greater than 1 and k=M/B;

B block output lines each connected to said k column output circuits of a respective block; and

a selection circuit configured to actively couple a single one of said B block output lines to a master output line at a time and thereby allow said k column output circuits associated with an actively coupled block output line to be actively connected to said master output line through said selection circuit.

11. The imager of claim 10, wherein said system is configured to control said selection circuit to sequentially select each of said B blocks by actively coupling said single one of said B block output lines of a selected block to said master output line.

12. The imager of claim 11, wherein said imager is further configured to sequentially cause each of said k column output circuits of said selected block to be actively coupled to said master output line via said single one of said B block output lines of said selected block.

13. The imager of claim 10, wherein said selection circuit comprises:

B switches, each of said B switches respectively associated with one of said B blocks to couple a respective one of the B block output lines with the master output line.

14. The imager of claim 13, wherein each of said B switches is a respective N-channel transistor having one source/drain connected to a respective one of said block output lines of an associated block and another source/drain connected to the master output line.

15. A CMOS imager, comprising:

a pixel array comprising a plurality of pixels, organized into N rows and M columns, wherein N and M are positive integers; and

M output circuits, each of said M output circuits for respectively outputting signals from M pixels of a selected row;

wherein said M output circuits are organized into B blocks, B being a positive integer, each of said B blocks comprisingk of said M output circuits, wherein k is a positive integer such that k=M/B;

B block output lines each coupled to said k output circuits of a respective block;

a master output line; and

a selection circuit, for actively coupling a single one of said B block output lines to said master output line at a time.

16. The imager of claim 15, wherein M is at least 1024 and M and k are greater than two.

17. A method of reading out signals of a selected row in an imager having pixels arranged in N rows by M columns through M column output circuits, the method comprising:

(a) operating said M column output circuits in B groups each having k column output circuits and a respective common group output line, each of said M column output circuits coupled to the N rows of a respective column;

(b) actively coupling only said respective common group output line of a selected one of said B groups to a master output node to receive said signals; and

(c) reading out said signals from each of said k column output circuits in the selected one of said B groups;

wherein M, B, and k are integers greater than two.

18. The method of claim 17, further comprising:

repeating steps (b) and (c) until said signals of all pixels of the selected row have been read out to said common output mode.

19. The method of claim 18, wherein in step (b) groups are selected in sequential order and in step (c) pixels of the selected group are read out in sequential order.

20. A method of reading out pixel signals of a selected row in an imager having pixels arranged in N rows by M columns through M output circuits, the method comprising:

(a) operating said M output circuits in B groups each having k output circuits and a common group output line;

(b) selecting only one at a time of said B groups by actively coupling said common group output line of a selected group to a master output node;

(c) reading out pixel signals from each of said k output circuits in the selected group; and

wherein M, B, and k are integers.

21. The method of claim 20, wherein M is greater than 1024 and k is more than two.

22. An imaging device, comprising:

an array of pixels, including source follower transistors, wherein a first set of adjacent columns of pixels of the array are connected to a first set of column output lines, and a second set of adjacent columns of pixels of the array are connected to a second set of column output lines;

a first set of greater than two column output circuits connected to the first set of column output lines to provide a first set of signals associated with a first set of pixels in a selected row and in the first set of adjacent columns, and a second set of greater than two column output circuits connected to the second set of column output lines to provide a second set of signals associated with a second set of pixels in the selected row and in the second set of adjacent columns; and

a first block select switch connected between the first set of column output circuits and a first array readout line and a second block select switch connected between the second set of column output circuits and the first array readout line, wherein the first block select switch, when enabled, allows the first set of signals to be driven onto the first array readout line, the second block select switch, when enabled, allows the second set of signals to be driven onto the first array readout line, and the first and second block select switches are to be enabled one-at-a-time.

23. The imaging device of claim 22, wherein the pixels include row select transistors.

24. The imaging device of claim 22, further comprising a first set of greater than two column output select switches connected to the first block select switch, and a second set of greater than two column output select switches connected to the second block select switch, wherein the first set of column output select switches are to be enabled one-at-a-time to allow the first set of signals to be driven to the first block select switch, and the second set of column output select switches are to be enabled one-at-a-time to allow the second set of signals to be driven to the second block select switch.

25. The imaging device of claim 24, wherein the first and second sets of column output select switches comprise n-channel transistors having first source/drain electrodes connected to receive the first and second sets of signals, respectively, second source/drain electrodes connected to provide the first and second sets of signals to the first and second block select switches, respectively, and gate electrodes connected to receive column output select signals.

26. The imaging device of claim 24, wherein the first set of column output select switches are to be enabled successively, and the second set of column output select switches are to be enabled successively.

27. The imaging device of claim 24, wherein the first set of column output select switches are to be enabled only while the first block select switch is enabled, and the second set of column output select switches are to be enabled only while the second block select switch is enabled.

28. The imaging device of claim 24, further comprising a first set of greater than two column output buffers connected to the first set of column output select switches to allow the first set of signals to be driven to the first set of column output select switches, and a second set of greater than two column output buffers connected to the second set of column output select switches to allow the second set of signals to be driven to the second set of column output select switches, wherein the first set of column output buffers comprises transistors having gate electrodes connected to receive the first set of signals and source/drain electrodes connected to provide the first set of signals to the first set of column output select switches, and the second set of column output buffers comprises transistors having gate electrodes connected to receive the second set of signals and source/drain electrodes connected to provide the second set of signals to the second set of column output select switches.

29. The imaging device of claim 22, wherein the first set of column output circuits is to further provide a third set of signals associated with the first set of pixels in the selected row and in the first set of adjacent columns, and the second set of column output circuits is to further provide a fourth set of signals associated with the second set of pixels in the selected row and in the second set of adjacent columns, and further comprising:

a third block select switch connected between the first set of column output circuits and a second array readout line, and a fourth block select switch connected between the second set of column output circuits and the second array readout line, wherein the third block select switch, when enabled, allows the third set of signals to be driven onto the second array readout line, the fourth block select switch, when enabled, allows the fourth set of signals to be driven onto the second array readout line, and the third and fourth block select switches are to be enabled one-at-a-time.

30. The imaging device of claim 29, wherein at least the first and third sets of signals together indicate an amount of charge collected by the first set of pixels, and at least the second and fourth sets of signals together indicate an amount of charge collected by the second set of pixels.

31. The imaging device of claim 30, wherein a difference between the first and third sets of signals indicates the amount of charge collected by the first set of pixels.

32. The imaging device of claim 29, further comprising a first set of greater than two column output select switches connected to the first block select switch, a second set of greater than two column output select switches connected to the second block select switch, a third set of greater than two column output select switches connected to the third block select switch, and a fourth set of greater than two column output select switches connected to the fourth block select switch, wherein the first set of column output select switches are to be enabled successively to allow the first set of signals to be driven to the first block select switch, the second set of column output select switches are to be enabled successively to allow the second set of signals to be driven to the second block select switch, the third set of column output select switches are to be enabled successively to allow the third set of signals to be driven to the third block select switch, and the fourth set of column output select switches are to be enabled successively to allow the fourth set of signals to be driven to the fourth block select switch.

33. The imaging device of claim 32, wherein the first set of column output select switches are to be enabled only while the first block select switch is enabled, the second set of column output select switches are to be enabled only while the second block select switch is enabled, the third set of column output select switches are to be enabled only while the third block select switch is enabled, and the fourth set of column output select switches are to be enabled only while the fourth block select switch is enabled.

34. The imaging device of claim 32, wherein the first set of column output select switches are to be enabled one-at-a-time, the second set of column output select switches are to be enabled one-at-a-time, the third set of column output select switches are to be enabled one-at-a-time, and the fourth set of column output select switches are to be enabled one-at-a-time.

35. The imaging device of claim 22, wherein the first block select switch comprises an n-channel transistor connected to the first set of column output circuits.

36. The imaging device of claim 35, wherein a source/drain electrode of the transistor is connected to the first set of column output circuits.

37. The imaging device of claim 22, wherein the first set of adjacent columns of pixels is adjacent to the second set of adjacent columns of pixels, and the first and second block select switches are to be activated successively.

38. The imaging device of claim 22, wherein each column output circuit of the first set of column output circuits produces at least two respective signals associated with a respective voltage indicative of charge collected by a respective pixel in the selected row of the array during a row readout.

39. The imaging device of claim 38, wherein at least one of the at least two respective signals associated with the respective voltage is an analog signal.

40. The imaging device of claim 22, wherein a third set of adjacent columns of pixels of the array are connected to a third set of column output lines, and further comprising a third set of greater than two column output circuits connected to the third set of column output lines to provide a third set of signals associated with a third set of pixels in the selected row and in the third set of adjacent columns, and a third block select switch connected between the third set of column output circuits and the first array readout line, wherein the third block select switch, when enabled, allows the third set of signals to be driven onto the first array readout line, and the first, second, and third block select switches are to be enabled one-at-a-time.

41. The imaging device of claim 40, wherein each of the first and second sets of column output circuits comprise at least 32 respective column output circuits.

42. A method, comprising:

generating first signals associated with a first row of pixels of an array of pixels of a CMOS imager during a frame readout;

transferring each of at least eight groups of signals selected from the first signals to a respective one of at least eight block output busses, wherein each of the groups of signals selected from the first signals are associated with adjacent pixels in the first row of pixels of the array; and

transferring only a single one of the groups of signals selected from the first signals from a respective one of the block output busses to a master readout bus at a time.

43. The method of claim 42, wherein transferring the groups of signals to the block output busses comprises transferring only a single one of the first signals of a corresponding one of the groups to the respective one of the block output buses at a time.

44. The method of claim 43, wherein in accordance with reading out the array from the array readout bus the column output circuits are to be enabled successively.

45. The method of claim 42, further comprising:

generating second signals associated with the first row of pixels of the array during the frame readout;

transferring each of at least eight groups of signals selected from the second signals to a respective one of the at least eight block output busses, wherein each of the groups of signals selected from the second signals are associated with adjacent pixels in the first row of pixels of the array; and

transferring only a single one of the groups of signals selected from the second signals from a respective one of the block output busses to the master readout bus at a time.

46. The method of claim 42, wherein generating the first signals and generating the second signals is completed at different times.

47. The method of claim 43, wherein generating the first signals and generating the second signals is begun at different times.

48. The method of claim 42, wherein generating the first signals and generating the second signals comprises storing the first and second signals in column output circuits during a same period of time.

49. The method of claim 48, wherein each pixel of the first row of pixels has a respective pixel value indicated by at least each respective corresponding one of the first signals and each respective corresponding one of the second signals.

50. The method of claim 49, further comprising determining a difference between said each respective corresponding one of the first signals and said each respective corresponding one of the second signals.

51. The method of claim 49, wherein each of the groups of signals selected from the first signals comprises more than two of the first signals.

52. The method of claim 46, wherein transferring the groups of signals selected from the first signals to the master readout bus and transferring the groups of signals selected from the second signals to the master readout bus comprise transferring the groups of signals selected from the first signals and transferring the groups of signals selected from the second signals to different lines of the master readout bus.

53. The method of claim 42, wherein each of the groups of signals selected from the first signals comprises more than two of the first signals.

54. The method of claim 42, wherein transferring the groups of signals to the master readout bus comprises passing at least one of the first signals through at least one transistor channel.

55. The method of claim 54, wherein transferring the groups of signals to the block output busses comprises passing at least one of the first signals through at least one transistor channel.

56. The method of claim 42, wherein transferring the groups of signals to the master readout bus comprises successively transferring each of the groups of signals and successively transferring the respective signals within each of the groups.