Low-noise active pixel sensor for imaging arrays with global reset
First Claim
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1. An active-pixel sensor including a radiation detector in a plurality of active-pixel sensors organized into a sensor array, said active-pixel sensor comprising:
- a transistor amplifier having an input and an output, its input connected to said radiation detector for generating an electrical signal output having a magnitude that is a function of the charge input from the radiation detector;
a first switch connected to said transistor amplifier for impressing the electrical signal from said transistor amplifier onto an output line;
a variable resistance connected between said transistor amplifier and said radiation detector for resetting the charge input of said transistor amplifier to a predetermined signal level; and
a second switch connected to said transistor amplifier and said variable resistance for providing a current source to said transistor amplifier during reset.
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Abstract
An imaging array of active pixel sensors uses a reset amplifier in each pixel in a four transistor CMOS implementation. The reset amplifier acts as a variable resistance in the source-follower amplifier feedback circuit. The variable resistance is controlled by a range reset voltage applied to the reset amplifier thereby nulling the photodiode reset noise. The ramp reset voltage is applied to all reset amplifiers of all pixels at the same time, thereby providing for reset of the entire array at the same time, i.e., global reset.
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Citations
20 Claims
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1. An active-pixel sensor including a radiation detector in a plurality of active-pixel sensors organized into a sensor array, said active-pixel sensor comprising:
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a transistor amplifier having an input and an output, its input connected to said radiation detector for generating an electrical signal output having a magnitude that is a function of the charge input from the radiation detector;
a first switch connected to said transistor amplifier for impressing the electrical signal from said transistor amplifier onto an output line;
a variable resistance connected between said transistor amplifier and said radiation detector for resetting the charge input of said transistor amplifier to a predetermined signal level; and
a second switch connected to said transistor amplifier and said variable resistance for providing a current source to said transistor amplifier during reset. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. An active-pixel sensor including a radiation detector in a two-dimensional array of active-pixel sensors organized into rows and columns of sensors, comprising:
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a transistor amplifier having an input and an output, its input connected to said radiation detector for generating an electrical signal output having a magnitude that is a function of the charge at its input generated by the radiation detector;
a first switch connected to said transistor amplifier for impressing the electrical signal of its output onto a column output line;
a variable resistance connected between said transistor amplifier and said radiation detector for resetting the charge at said transistor amplifier input to a predetermined signal level; and
a second switch connected to said transistor amplifier and said variable resistance for providing a current source to said transistor amplifier during reset. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20)
a voltage source VSRC;
a current source ISRC; and
means for connecting the voltage source VSRC to said column output line during reset of the sensor, and connecting said current source ISRC to said column output line during readout of the sensor.
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19. The active-pixel sensor of claim 16 wherein said second switch comprises a transistor with a first leg, a second leg and a gate, the transistor being connected to said transistor amplifier and said variable resistance by the first leg and to a row output line by the second leg.
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20. The active-pixel sensor of claim 19 wherein the second switch transistor connects a current source to said row output line during reset of the sensors, and a voltage source to said row output line during readout of the sensors.
Specification