Pixel circuit with constant voltage biased photodiode and related imaging method
AssigneeVarex Imaging Corporation
InventorsArundhuti Ganguly, Pieter Gerhard Roos
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Abstract
An imaging system includes a plurality of pixel circuits each having a photodiode, a biasing circuit and a charge-to-voltage converter. The photodiode is configured to generate charges in response to light or radiation. The biasing circuit is configured to provide a constant bias voltage across the photodiode so as to drain the charges generated by the photodiode. The charge-to-voltage converter is configured to accumulate the charges drained by the biasing circuit and convert the accumulated charges into a corresponding output voltage.
Claims16
An imaging system having a pixel array that includes a plurality of pixel circuits, each pixel circuit comprising:
- a photodiode configured to generate charges in response to light or radiation;
- a biasing circuit configured to provide a constant bias voltage across the photodiode to drain the charges generated by the photodiode;
- a first charge-to-voltage converter configured to accumulate the charges drained by the biasing circuit and convert the accumulated charges into a corresponding output voltage;
- a second charge-to-voltage converter;
- and
- a gain-switching circuit configured to select the second charge-to-voltage converter to accumulate the charges generated by the photodiode in response to detection of the output voltage exceeding a threshold voltage.
An imaging method, comprising:
- maintaining a voltage established across a photodiode at a constant value to drain charges generated by the photodiode in response to light or radiation;
- accumulating the charges drained from the photodiode in a first charge-to-voltage converter and converting the accumulated charges into a corresponding output voltage during an image acquisition period;
- and
- acquiring a signal sample by reading the output voltage during a readout period subsequent to the image acquisition period.
Dependencies are inferred from the claim text.