Image sensor array with picture element sensor testability
First Claim
1. In a two dimensional, image scanner array having pixel sensor circuits arranged in rows and columns, apparatus for testing said pixel sensor circuits comprising:
- a reset supply providing a source of selectable test voltages;
a reset device for resetting a voltage of a photo-sensitive device in a pixel sensor circuit to a test voltage from the reset supply; and
a sensing circuit for sensing an output of the pixel sensor circuit in response to an application of the test voltage to the photo-sensitive device.
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Accused Products
Abstract
A picture element sensor circuit in an image array scanner is tested by driving a reset FET with a controllable voltage to set the reverse-bias voltage across the photo-diode at any selectable level of test voltage. In this way each pixel sensor circuit in the array may be tested as if it had received a desired amount of illumination. Alternatively, the drive voltage for the reset transistor is provided over the column output line. The controllable test voltage can be applied to the column line when no row access enable signal is applied to the array. In this situation the column line source follower circuit is inhibited by the row access FETs. Thus, a separate test voltage can be driven onto the column line, through a reset switch, and connected through the pixel sensor reset transistor to the pixel sensor photo-diode. The variable reset voltage, that is driven onto the column line, can be varied between ground and the normal bias voltage VDD for the pixel sensor by use of parallel connected P-channel FET and N-channel FET.
57 Citations
16 Claims
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1. In a two dimensional, image scanner array having pixel sensor circuits arranged in rows and columns, apparatus for testing said pixel sensor circuits comprising:
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a reset supply providing a source of selectable test voltages; a reset device for resetting a voltage of a photo-sensitive device in a pixel sensor circuit to a test voltage from the reset supply; and a sensing circuit for sensing an output of the pixel sensor circuit in response to an application of the test voltage to the photo-sensitive device. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A method for testing a focal plane image scanner array comprising the steps of:
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a) providing a reset supply for a pixel sensor circuit for applying a selectable test voltage; b) resetting a voltage across a photo-sensitive device in the pixel sensor circuit to the selectable test voltage; c) driving the voltage across the photo-sensitive device onto an output line after the voltage across the photo-sensitive device has been reset to the selectable test voltage by said resetting step; and d) providing from the output line an output test signal proportional to the voltage across the photo-sensitive device. - View Dependent Claims (8, 9, 10)
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11. An image scanner array having a plurality of pixel sensing circuits, each pixel sensing circuit comprising:
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a photo-diode back biased by a reset voltage; a source follower field effect transistor circuit for driving an output signal proportional to an operative signal corresponding to the voltage across the photo-diode; a reset voltage source for supplying as the reset voltage a test voltage; a reset field effect transistor for applying the reset voltage to back-bias the photo-diode; and a timer for enabling first the reset field effect transistor to apply the test voltage as an operative voltage across the photodiode and thereafter for enabling the source follower circuit to drive an output signal proportional to the operative voltage. - View Dependent Claims (12, 13, 14, 15, 16)
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Specification