Reset-marking pixel sensor
AssigneeRambus Inc.
InventorsJie Shen, Yueyong Wang, James E. Harris
Life of this patent
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Abstract
A self-resetting pixel having a memory element to record occurrence of an asynchronous pixel reset and circuitry to enable the memory element to be digitally sampled and cleared is disclosed, together with embodiments of digital image sensors formed by arrays or other collections of such pixels. By marking occurrence of asynchronous reset events within an in-pixel memory element that may be digitally oversampled during an exposure interval (i.e., repeatedly read-out in the form of, for example, a single-bit), it becomes possible to check for and detect asynchronous pixel reset events frequently and efficiently.
Claims21
A pixel for use in a digital image sensor, the pixel comprising:
- a photosensitive element that exhibits an output signal in response to incident light;
- a comparator to receive the output signal from the photosensitive element and to assert an asynchronous-reset signal upon detecting that the output signal exceeds a threshold;
- a reset circuit to reset the photosensitive element to an initial condition in response to assertion of the asynchronous-reset signal;
- a memory element to store, in response to assertion of the asynchronous-reset signal, a digital value indicating that the photosensitive element has been reset;
- and
- output circuitry to output from the pixel onto a multiplexed read-out line of the digital image sensor at respective times (i) a digital signal representative of the digital value stored within the memory element in a digital sampling operation, and (ii) an analog signal representative of the output signal of the photosensitive element in an analog sampling operation.
A method of operation within a pixel for use in a digital image sensor, the method comprising:
- generating, within a photosensitive element, an output signal that changes in response to incident light;
- asynchronously determining whether the output signal exceeds a threshold;
- in response to determining that the output signal exceeds the threshold, resetting the output signal to a level that does not exceed the threshold and storing a digital value within the pixel to indicate that the output signal has been reset;
- and
- outputting from the pixel onto a multiplexed read-out line of the digital image sensor at respective times (i) a digital signal representative of the digital value stored within the pixel, and (ii) an analog signal representative of the output signal of the photosensitive element.
A pixel for use in a digital image sensor, the pixel comprising:
- a photosensitive element to generate an output signal that changes in response to incident light;
- a comparator to receive the output signal from the photosensitive element and to assert an asynchronous-reset signal when the output signal exceeds a threshold;
- a capacitive node having a capacitance sufficient to hold a charge level indicative of a first logic state for at least a predetermined duration;
- a first switching element coupled between a first supply voltage node and the capacitive node, the first switching element having a control input coupled to receive the asynchronous-reset signal from the comparator;
- and
- a second switching element coupled between the first supply voltage node and the photosensitive element, the second switching element having a control input coupled to receive the asynchronous-reset signal from the comparator;
- and
- a third switching element coupled between the capacitive node and a second supply voltage node.
Dependencies are inferred from the claim text.