Low-noise active-pixel sensor for imaging arrays with high speed row reset
AssigneePictos Technologies, Inc.
InventorsLester J. Kozlowski, David L. Standley
Life of this patent
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Abstract
An active pixel sensor circuit including a photodetector, a first MOS transistor functioning as the driver of a source follower amplifier during signal readout, a second MOS transistor serving as a pixel readout transistor, a third MOS transistor serving as a photodetector reset transistor, and a reset noise cancellation circuit including a fourth MOS transistor, first and second capacitances, and an amplifier having a gain which is a specified multiple of the ratio of the first to the second capacitance. The first capacitance is connected in parallel to the photodector. The amplifier reduces the reset noise caused by resetting the photodector without having to implement correlated double sampling.
Claims30
An active pixel circuit having a photodetector, a source follower driver transistor, a row select transistor, a reset transistor, and a fourth transistor, the circuit comprising:
- a first capacitor connected in parallel with the photodetector;
- a second capacitor connected between the reset transistor and the fourth transistor;
- and
- a feedback amplifier connected between the row select transistor and the fourth transistor, wherein the gain of the amplifier equals a specified multiple of a reciprocal of a linear attenuation factor.
An active pixel sensor circuit comprising:
- (a) a photodetector element having a node;
- (b) a first transistor having a control leg connected to the node and second and third legs, the third leg being connected to a power supply voltage;
- (c) a second transistor having a control leg and fourth and fifth legs, the fourth leg connected to the second leg of the first transistor;
- (d) a third transistor having a control leg and sixth and seventh legs, the seventh leg being connected to a reset voltage source;
- (e) a fourth transistor having a control leg and eighth and ninth legs;
- (f) a first capacitance connected in parallel to the photodector;
- and
- (g) a second capacitance formed between the eighth leg and the sixth leg.
In an active pixel circuit including a photodetector, a source follower driver MOS transistor, a row select MOS transistor, a reset MOS transistor, a fourth MOS transistor, and first and second capacitances, the first capacitance connected in parallel to the photodetector, a method for reducing reset noise, the method comprising:
- arranging the first and second capacitances to apply a ratio of the values thereof to a voltage on one of them;
- reading out the voltage on the photodetector;
- resetting the photodetector;
- and
- canceling reset noise created by resetting the photodetector by applying a gain which is a specified multiple of the inverse of the ratio to generate a noise cancellation signal for supply to the fourth transistor.
In an imager pixel including a photodetector having a node and further having first, second, third and fourth transistors, a method of improving performance comprising:
- creating a first capacitance in parallel with the photodetector;
- creating a second capacitance in the pixel adjacent the node, the first and second capacitances having a ratio;
- and
- employing an amplifier having a gain which is a specified multiple of the ratio to cancel reset noise resulting from resetting the photodetector.
An imager pixel comprising:
- a photodetector;
- a first capacitance connected in parallel to the photodector;
- a second capacitance adjacent the photodetector and connected so as to supply a voltage on the first capacitance to the photodetector while multiplying that voltage by the ratio of the second capacitance to the first capacitance;
- a first transistor means for functioning as the driver of a source follower amplifier during signal readout;
- second transistor means for controlling signal readout;
- third transistor means for serving as a reset switch;
- and
- a fourth transistor means for transferring a voltage to the first capacitance.
Dependencies are inferred from the claim text.