Method and circuit for determining the response curve knee point in active pixel image sensors with extended dynamic range

• US 20070195183A1
• Filed: 04/18/2007
• Published: 08/23/2007
• Est. Priority Date: 08/05/2003
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Ovsiannikov, Ilia, Kaplinsky, Michael, Cho, Kwang-Bo
• Granted Patent: US 7,768,563 B2
• Time in Patent Office: Days
• US Class Current: 348/308
• CPC Class Codes: H04N 25/571 involving a non-linear response
• CPC Class Codes: H04N 25/575 with a response composed of multiple slopes

Abstract

An apparatus and method for measuring the breakpoint of a response curve representing the voltage output of an image array having an extended dynamic range. By flooding a light-opaque pixel with a charge and then applying an intermediate reset voltage to the pixel, the signal is read from the pixel and stored. The full reset voltage is applied to the pixel, and then the signal in the pixel is read and stored. The voltage output difference is the difference between the first and second stored signal. The voltage output difference is then used to determine the voltage of the knee point. Further, a conventional saturated pixel can be reset with an intermediate reset just prior to readout. The resulting signal can then be used to determine the voltage of the knee point.

Claims

1-32. -32. (canceled)

33. A method of operating pixel of pixel array, said method comprising:

flooding a pixel in said array to clear any stored signal;

applying a first reset voltage to a charge storage area of said pixel;

sampling a first voltage signal from said charge storage area;

applying a second reset voltage to said charge storage area;

sampling a second voltage signal from said charge storage area; and

determining a difference between said first and second sampled voltage signals.

34. The method of claim 33, wherein said first reset voltage is an intermediate reset voltage, which is less than a full reset voltage.

35. The method of claim 34, wherein said second reset voltage said full reset voltage.

36. The method of claim 33, wherein said first reset voltage is a higher voltage than said second reset voltage.

37. The method of claim 36, wherein said determining further comprises:

determining said difference in a differential amplifier.

38. The method of claim 37, further comprising:

converting said difference into a digital form.

39-70. -70. (canceled)

71. An imager array comprising:

a pixel array;

a readout circuit for reading signals from said array; and

a control circuit for operating said pixel array and said readout circuit, said control circuit being configured to flood a pixel in said array to clear any stored signal in a charge storage area, apply a first reset voltage to said charge storage area of said pixel, sample a first voltage signal from said charge storage area, apply a second reset voltage to said charge storage area, sample a second voltage signal from said charge storage area, and determine a difference between said first and second sampled voltage signals.

72. The imager of claim 71, wherein said first reset voltage is an intermediate reset voltage, which is less than a full reset voltage.

73. The imager of claim 72, wherein said second reset voltage said full reset voltage.

74. The imager of claim 73, wherein said first reset voltage is a higher voltage than said second reset voltage.

75. An imager array, comprising:

a pixel array

a flood circuit for flooding said pixel, said flood circuit being selectively coupled to said pixel; and

a reset circuit for resetting said pixel, said reset circuit being selectively coupled to said pixel.

76. The imager of claim 75, wherein said reset circuit is configured to provide first and second non-zero voltages to said pixel.

77. The imager of claim 76, wherein said flood circuit is configured to said pixel to ground.