Method for operating a high sensitivity active pixel
First Claim
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1. A method comprising:
- allowing light to be incident upon a photodetector circuit to thereby generate an input signal representing the light, the input signal being applied to a gate of a first field effect transistor (FET);
applying a first control signal to a drain of the first FET and thereby generating an output current at a source of the first FET; and
accumulating charge in a capacitor coupled to the source of the first FET.
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Abstract
A method of operating a high sensitivity active pixel for use in metal oxide semiconductor (MOS) image sensor circuits. Light is allowed to be incident upon a photodetector circuit to thereby generate an input signal that represents the light. The input signal is applied to a gate of a first field effect transistor (FET). A control signal is applied to a drain of the FET and thereby generates an output current at a source of the FET. Charge is accumulated in a capacitor that is coupled to the source of the FET, where a voltage across the capacitor represents the detected incident light.
26 Citations
9 Claims
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1. A method comprising:
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allowing light to be incident upon a photodetector circuit to thereby generate an input signal representing the light, the input signal being applied to a gate of a first field effect transistor (FET);
applying a first control signal to a drain of the first FET and thereby generating an output current at a source of the first FET; and
accumulating charge in a capacitor coupled to the source of the first FET. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
capturing a signal value related to a voltage across the capacitor while the digital pulse is asserted.
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4. The method of claim 1 further comprising:
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asserting a second control signal, that is the complement of the first control signal, to reset the photodetector circuit; and
capturing a reset value related to a voltage across the capacitor immediately after deasserting the second control signal.
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5. The method of claim 4 wherein the second control signal is applied to a drain of a reset FET coupled to a photodiode in the photodetector circuit.
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6. The method of claim 3 further comprising:
asserting a select signal at a gate of a second FET having a drain coupled to the capacitor through a source follower, to provide a current representative of the voltage across the capacitor.
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7. The method of claim 6 further comprising:
raising the voltage at a gate of the source follower in response to the select signal being asserted.
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8. The method of claim 7 wherein the voltage at the gate of the source follower is raised by at least one threshold voltage (Vt) in response to the select signal being asserted.
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9. The method of claim 3 further comprising:
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converting the captured signal value into digital format representing part of a digital image; and
transferring the digital captured signal value to a personal computer.
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Specification