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US 8,009,212 B2Granted
Image processing system with a 4-T pixel and method thereof capable of reducing fixed pattern noise
AssigneeUnited Microelectronics Corp.
InventorsYuan-Che Lee, Jhy-Jyi Sze, Chiao-Fu Chang
Life of this patent
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Abstract
Circuitry for reducing fixed pattern noise in an image processing system with a 4-T (4 transistors) pixel and a method thereof is proposed. The image processing system includes two voltage sources, two current sources, a 4-T pixel, a second portion of a linearized source follower, a ping pong memory, a PGA, and auto-zero circuitry. By coupling the auto-zero circuitry to the PGA, an open loop is formed to clamp the output of an op amp of the PGA to a stable reference when resetting the PGA so as to remove DC offsets at the output terminal of the op amp.
Claims18
An image processing system comprising:
- a photodiode (for generating data according to received light);
- a 4-T (4-transistor) pixel coupled to the photodiode for transferring the data received from the photodiode, the 4-T transistor including a first portion of a linearized source follower;
- a second portion of the linearized source follower coupled to the first portion of the linearized source follower;
- a ping pong memory coupled to an output terminal of the second portion of the linearized source follower for transferring the data received from the photodiode through the 4-T pixel;
- a PGA (programmable gain amplifier) coupled to an output terminal of the ping pong memory for amplifying the data transferred from the output terminal of the ping pong memory;
- and
- auto-zero circuitry coupled to the PGA for eliminating a dc offset and noise of the PGA.
4 more elements
An image processing method comprising:
- resetting a 4-T pixel and a first portion of a ping pong memory;
- writing data from a photodiode to the first portion of the ping pong memory through the 4-T pixel;
- auto-zero circuitry resetting an output of a PGA (programmable gain amplifier) to generate a stable reference;
- and
- writing the data from the first portion of the ping pong memory to the PGA.
2 more elements
An image processing method comprising:
- switching on a first switch of a first portion of a ping pong memory;
- changing a first reset signal from a first potential to a second potential to switch on a reset switch of a 4-T (4-transistor) pixel;
- after the first switch of the first portion of the ping pong memory and the reset switch of the 4-T pixel are switched on, switching on a second switch of the first portion of the ping pong memory;
- after the second switch of the first portion of the ping pong memory is switched on, changing the first reset signal from the second potential to the first potential to switch off the reset switch of the 4-T pixel;
- after the reset switch of the 4-T pixel is switched off, switching off the second switch of the first portion of the ping pong memory;
- changing a first transferring signal from the first potential to the second potential to switch on a transmission switch of the 4-T pixel so as to start a data-writing process from the 4-T pixel to the first portion of the ping pong memory;
- after performing the data-writing process from the 4-T pixel to the first portion of the ping pong memory, changing the first transferring signal from the second potential to the first potential to switch off the transmission switch of the 4-T pixel, and switching off the first switch of the first portion of the ping pong memory;
- after switching off the first switch of the first portion of the ping pong memory, switching on a third switch of the first portion of the ping pong memory;
- switching on a first selection switch and a second selection switch of a PGA (programmable gain amplifier);
- after the first selection switch and the second selection switch of the PGA are switched on, changing a second reset signal from the first potential to the second potential to switch on first and second reset switches of auto-zero circuitry, and third and fourth reset switches of the PGA to reset the PGA and the auto-zero circuitry;
- after the PGA and the auto-zero circuitry are reset, changing the second reset signal from the second potential to the first potential to switch off the first and second reset switches of the auto-zero circuitry, and the third and fourth reset switches of the PGA;
- after the first and second reset switches of the auto-zero circuitry, and the third and fourth reset switches of the PGA are switched off, changing a second transferring signal from the first potential to the second potential to switch on a first transmission switch of the PGA, and second and third transmission switches of the auto-zero circuitry so as to start a data-writing process from the first portion of the ping pong memory to the PGA;
- after performing the data-writing process from the first portion of the ping pong memory to the PGA, changing the second transferring signal from the second potential to the first potential to switch off the first transmission switch of the PGA, and the second and third transmission switches of the auto-zero circuitry;
- and
- after the first transmission switch of the PGA, and the second and third transmission switches of the auto-zero circuitry are switched off, switching off the first and second selection switches of the PGA.
12 more elements
Dependencies are inferred from the claim text.