Method and apparatus for increasing retention time in image sensors having an electronic shutter
First Claim
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1. In a pixel having an electronic shutter, a method of increasing the retention time of the electronic shutter comprising:
- a) employing a reset signal to drive a diode node to a predetermined voltage immediately after an integration is complete and during readout, and to substantially inhibit subthreshold leakage from a storage node; and
b) employing a sample signal to control a pass gate, said sample signal having a state where said sample signal is a negative voltage.
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Abstract
In a pixel having an electronic shutter, a method of increasing the retention time of the electronic shutter is disclosed. A reset signal is employed to drive a diode node to a predetermined voltage immediately after integration is completed. A sample signal is employed to control a pass gate. The sample signal includes a state where the sample signal is a negative voltage.
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Citations
11 Claims
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1. In a pixel having an electronic shutter, a method of increasing the retention time of the electronic shutter comprising:
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a) employing a reset signal to drive a diode node to a predetermined voltage immediately after an integration is complete and during readout, and to substantially inhibit subthreshold leakage from a storage node; and
b) employing a sample signal to control a pass gate, said sample signal having a state where said sample signal is a negative voltage. - View Dependent Claims (2)
employing metal to shield a source node of the pass gate.
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3. A pixel controller comprising:
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a) a reset generator for providing a reset signal to control a first transistor and for driving the reset signal to a predetermined voltage immediately after integration is complete; and
b) a sample signal generator, for providing a sample signal to control a pass gate. - View Dependent Claims (4)
a row signal generator for generating a row signal that selectively reads out a value on the storage node and selectively provides said value to a bitline.
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5. In an image capture system including a pixel, said pixel having a first node and a second node, a method of increasing the retention time of a pixel value on the second node, said method comprising:
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a) asserting a reset signal to reset a first node to a predetermined value;
b) asserting a sample signal for a predetermined integration time to store a pixel value on the second node;
c) driving said sample signal to a negative voltage after said predetermined integration time; and
d) asserting said reset signal after said sample signal is driven to said negative voltage;
wherein asserting said reset signal and driving of said sample signal to said negative voltage continues throughout the readout period. - View Dependent Claims (6, 7, 8, 9, 10)
reading out the pixel values.
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7. The method of claim 5 further comprising:
reading out a first row of pixels.
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8. The method of claim 7 further comprising:
reading out a second row of pixels.
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9. The method of claim 5 wherein the image capture system is operating in a frame mode.
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10. The method of claim 5 wherein the image capture system is operating in a row mode.
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11. A method of frame mode operation of a pixel array, said array having a plurality of pixel cells, each pixel cell having a reset transistor for receiving a reset signal, a sample transistor for receiving a sample signal, said method comprising:
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a) asserting a reset signal;
b) asserting a sample signal;
c) deasserting the reset signal to begin integration;
d) deasserting the sample signal to stop integration and driving said sample signal to a negative voltage;
e) asserting the reset signal immediately after the sample signal is deasserted; and
f) reading out a pixel value for a first row.
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Specification