Method and circuit for determining the response curve knee point in active pixel image sensors with extended dynamic range
First Claim
1. A method of operating a pixel of a pixel array, said pixel including a reset transistor having a gate, said method comprising:
- applying a first reset voltage to said gate of said reset transistor, said reset transistor affecting a charge at a charge storage area of said pixel, said first reset voltage having an amplitude sufficient to cause conduction of said reset transistor;
sampling a first voltage signal at said charge storage area of said pixel after said first reset voltage is applied;
applying a second reset voltage to said gate of said reset transistor, said second reset voltage having an amplitude sufficient to cause conduction of said reset transistor, wherein one of said first and second reset voltages has a larger amplitude than the other;
sampling a second voltage signal at said charge storage area after said second reset voltage; and
determining a difference between said first and second sampled voltage signals.
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Accused Products
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.
13 Citations
27 Claims
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1. A method of operating a pixel of a pixel array, said pixel including a reset transistor having a gate, said method comprising:
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applying a first reset voltage to said gate of said reset transistor, said reset transistor affecting a charge at a charge storage area of said pixel, said first reset voltage having an amplitude sufficient to cause conduction of said reset transistor; sampling a first voltage signal at said charge storage area of said pixel after said first reset voltage is applied; applying a second reset voltage to said gate of said reset transistor, said second reset voltage having an amplitude sufficient to cause conduction of said reset transistor, wherein one of said first and second reset voltages has a larger amplitude than the other; sampling a second voltage signal at said charge storage area after said second reset voltage; and determining a difference between said first and second sampled voltage signals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. An imager comprising:
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a pixel array including a pixel having a reset transistor with a gate; 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; apply a first reset voltage to said gate of said reset transistor to affect a charge at a charge storage area of said pixel, said first reset voltage having an amplitude sufficient to cause conduction of said reset transistor; apply a first sampling signal to sample a first voltage signal at said charge storage area of said pixel after said first reset voltage is applied; apply a second reset voltage to said gate of said reset transistor to affect a charge at said charge storage area of said pixel, said second reset voltage having an amplitude sufficient to cause conduction of said reset transistor, wherein one of said first and second reset voltages has a larger amplitude than the other; apply a second sampling signal to sample a second voltage signal at said charge storage area after said second reset voltage is applied; and determine a difference between said first and second sampled voltage signals. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. An imager comprising:
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a pixel array; a flood circuit for flooding said pixel, said flood circuit being selectively coupled to said pixel, wherein said flood circuit is configured to connect said pixel to ground; and a reset circuit for resetting said pixel, said reset circuit configured to selectively couple said pixel to said flood circuit, wherein said reset circuit is configured to provide the ground and first and second non-zero voltages to said pixel. - View Dependent Claims (27)
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Specification