CMOS image sensor with active reset and 4-transistor pixels
AssigneeMicron Technology, Inc.
InventorRay A. Mentzer
Life of this patent
Estimating the term…
Abstract
A CMOS image sensor implementing a low noise active reset operation uses control circuitry outside a pixel sensor array and transistors in a pixel sensor as parts of an amplifier that charges a photodiode node. In one configuration, a reference transistor in the control circuit controls a current mirrored to a column line, and each pixel sensor in the corresponding column contains a transistor that acts as half of a differential pair when the row containing the pixel sensor is selected. A 4-transistor pixel sensor can be implemented using only NMOS transistors with PMOS transistors in the control circuitry used to complete an amplifier circuit.
Claims14
An image sensor comprising:
- an array of pixel sensors;
- and
- a control circuit outside the array, wherein the control circuit comprises a first transistor having a gate under control of a reference signal and a current mirror circuit coupled to drive a control line of the array with a mirrored current that mirrors a current through the first transistor, wherein
- each of the pixel sensors that are coupled to the control line comprises:
- a photodiode;
- a second transistor having a gate coupled to a node of the photodiode;
- and
- a third transistor having a terminal coupled to the node of the photodiode and a gate coupled to a terminal of the second transistor.
A reset method for an image sensor, comprising:
- connecting a selected pixel sensor from an array of pixel sensors to a current mirror circuit in a control circuit outside the array;
- applying a reference signal to a gate of a first transistor in the control circuit, wherein the first transistor controls a mirrored current that the current mirror circuit drives through a second transistor, the second transistor having a gate coupled to a node of a photodiode in the selected pixel sensor;
- and
- applying a voltage to a first terminal of a third transistor, wherein the third transistor has a second terminal coupled to the node of the photodiode in the selected pixel sensor and a gate coupled to a terminal of the second transistor, wherein the third transistor drives a voltage on the node to follow the reference signal.
Dependencies are inferred from the claim text.