Image sensor with correlated double sampling technique using switched-capacitor technology
First Claim
1. A method of processing an output signal of an image sensor pixel in readout circuitry having a first capacitor element coupled to a second capacitor element, comprising the steps of:
- a. applying a reference voltage VREF to the first and the second capacitor elements;
b. applying a first sample signal VS1 from the image sensor pixel to the first capacitor element placing a charge on the first capacitor element;
c. transferring the charge from the first capacitor element to the second capacitor element;
d. applying a second sample signal VS2 from the image sensor pixel to the first capacitor element placing a charge on the first capacitor element; and
e. transferring the charge from the second capacitor element to the first capacitor element so as to provide an output signal that is a function of the difference between the second sample signal VS2 and the first sample signal VS1.
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Accused Products
Abstract
The invention is directed to a method and apparatus for processing an output signal of an image sensor pixel in a manner that will substantially avoid fixed pattern noise contributed by the readout circuitry. The method comprises applying a reference voltage VREF to first and second capacitor elements that are coupled together at a common terminal, applying a first sample signal VS1 from the image sensor pixel to the first capacitor element placing a charge on it, transferring the charge from the first capacitor element to the second capacitor element, applying a second sample signal VS2 from the image sensor pixel to the first capacitor element placing a charge on it, and transferring the charge from the second capacitor element to the first capacitor element so as to provide an output signal that is a function of the difference between the second sample signal VS2 and the first sample signal VS1. In particular VO=VS2−VS1+VREF. The readout circuitry comprises a first capacitor element having first and second terminals, a second capacitor element having first and second terminals, an amplifier having an input terminal and an output terminal with the input terminal connected to the second terminals of the first and second capacitor elements. The readout circuitry further includes a first switch adapted to be connected between a reference voltage and the first terminal of the first capacitor element, a second switch adapted to be connected between a pixel and the first terminal of the first capacitor element, a third switch adapted to be connected between a reference voltage and the first terminal of the second capacitor element, a fourth switch connected between the amplifier input terminal and the output terminal, a fifth switch connected between the second terminal of the second capacitor element and the amplifier output terminal, and a sixth switch connected between the first terminal of the first capacitor element and the amplifier output terminal. The readout circuitry also includes a controller for controlling the first to sixth switches. The amplifier may be a CMOS operational amplifier with a reference terminal for connection to a reference voltage and all of the switches may be CMOS transistors.
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Citations
23 Claims
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1. A method of processing an output signal of an image sensor pixel in readout circuitry having a first capacitor element coupled to a second capacitor element, comprising the steps of:
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a. applying a reference voltage VREF to the first and the second capacitor elements;
b. applying a first sample signal VS1 from the image sensor pixel to the first capacitor element placing a charge on the first capacitor element;
c. transferring the charge from the first capacitor element to the second capacitor element;
d. applying a second sample signal VS2 from the image sensor pixel to the first capacitor element placing a charge on the first capacitor element; and
e. transferring the charge from the second capacitor element to the first capacitor element so as to provide an output signal that is a function of the difference between the second sample signal VS2 and the first sample signal VS1. - View Dependent Claims (2, 3)
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4. A method of processing an output signal of an image sensor pixel in readout circuitry having an operational amplifier with an input terminal, a reference terminal and an output terminal, a first capacitor element having first and second terminals with the second terminal coupled to the input terminal and a second capacitor element having first and second terminals with the second terminal coupled to the input terminal, comprising the steps of:
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a. connecting the operational amplifier reference terminal to a reference voltage VREF;
b. applying the reference voltage VREF to the first terminals of the first and the second capacitor elements;
c. applying a first sample signal VS1 from the image sensor pixel to the first terminal of the first capacitor element placing a charge on the first capacitor element;
d. transferring the charge from the first capacitor element to the second capacitor element;
e. applying a second sample signal VS2 from the image sensor pixel to the first terminal of the first capacitor element placing a charge on the first capacitor element; and
f. transferring the charge from the second capacitor element to the first capacitor element so as to provide an output signal VO on the operational amplifier output terminal that is a function of the difference between the second sample signal VS2 and the first sample signal VS1. - View Dependent Claims (5, 6)
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7. A method of processing an output signal of an image sensor pixel in readout circuitry having an operational amplifier with an input terminal, a reference terminal connected to a first reference voltage and an output terminal, a first capacitor element having first and second terminals with the second terminal coupled to the input terminal, a second capacitor element having first and second terminals with the second terminal coupled to the input terminal, first switch means adapted to be connected between a second reference voltage and the first capacitor element first terminal, second switch means adapted to be connected between a pixel and the first capacitor element first terminal, third switch means adapted to be connected between a third reference voltage and the second capacitor element first terminal;
- fourth switch means connected between the operational amplifier input terminal and the output terminal;
fifth switch means connected between the second capacitor element second terminal and the operational amplifier output terminal; and
sixth switch means connected between the first capacitor element first terminal and the operational amplifier output terminal, comprising the steps of;
a. opening all of the switch means;
b. closing the first, third and fourth switch means;
c. opening all of the switch means;
d. closing the second and fifth switch means;
e. opening the fifth switch means and closing the fourth switch means;
f. opening all of the switch means;
g. closing the third and sixth switch means;
h. reading the output voltage Vo on the operational amplifier output terminal. - View Dependent Claims (8, 9, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
- fourth switch means connected between the operational amplifier input terminal and the output terminal;
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13. Readout circuitry for image sensor pixels comprising:
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first capacitor means having first and a second terminals;
second capacitor means having first and a second terminals;
amplifier means having an input terminal and an output terminal, wherein the second terminals of the first and second capacitor means are connected to the amplifier means input terminal;
first switch means connected to the first capacitor means first terminal;
second switch means connected to the second capacitor means first terminal;
third switch means connected between the amplifier means input terminal and output terminal;
fourth switch means connected between the second capacitor means second terminal and the amplifier means output terminal; and
fifth switch means connected between the first capacitor means first terminal and the amplifier means output terminal.
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Specification