Photodiode-type pixel for global electronic shutter and reduced lag

• US 20030103153A1
• Filed: 10/16/2002
• Published: 06/05/2003
• Est. Priority Date: 02/17/1998
• Status: Active Grant

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Micron Technology, Inc.
• Inventors: Fossum, Eric R.
• Granted Patent: US 7,095,440 B2
• Time in Patent Office: Days
• US Class Current: 348/308
• CPC Class Codes: H01L 27/14609 Pixel-elements with integrated switching, control, storage or amplification elements scanning details of imagers (circuitry of solid-state image sensors H04N25/00); circuitry of imagers H04N25/70
• CPC Class Codes: H04N 25/62 Detection or reduction of noise due to excess charges produced by the exposure, e.g. smear, blooming, ghost image, crosstalk or leakage between pixels
• CPC Class Codes: H04N 25/626 Reduction of noise due to residual charges remaining after image readout, e.g. to remove ghost images or afterimages
• CPC Class Codes: H04N 25/672 between adjacent sensors or output registers for reading a single image

Abstract

Operation for global electronic shutter photodiode-type pixels. In a first mode of operation, lag is reduced through global reset of the photodiode array and fixed pattern noise is eliminated through comparison of the photosignal level and the reset level of the floating drain. In a second mode of operation, simultaneous integration and readout processes are achieved through cessation of spill charges over the transfer gate. In a third mode of operation, regulation of the reset photodiode and transfer gate enables voltage gain between the photodiode and the sense node.

Claims

1. An active pixel sensor, comprising:

a photodiode part operating to accumulate a signal indicative of incoming light;

a floating diffusion part, selectively connected to receive said signal from said photodiode;

a transfer barrier gate, having a bias level which allows said signal to pass from said photodiode part to said floating diffusion part;

a buffer, connected to sample a signal on said floating diffusion part; and

at least one flood and spill control part, connected to at least said photodiode and controlling flooding at least said at least one part to provide a known initial condition on said at least one part.

2. The sensor as in claim 1, further comprising a shutter gate, connected to said photodiode, and having a shuttered bias level which is lower than said bias level on said transfer barrier gate, and which forces all charge in said photodiode to be drained prior to reaching a potential of said transfer barrier gate.

3. The sensor of claim 2, wherein said flood and spill control part controls flood and spill to both said photodiode part and said floating diffusion part.

4. The sensor of claim 1, wherein said bias level on said transfer barrier is a level that allows incoming charge on said photodiode to trickle into said floating diffusion.

5. The sensor of claim 1, wherein said bias level on said transfer barrier is varied between a first level that accumulates charge in said photodiode, and a second level that passes charge in said photodiode to said floating diffusion.

6. The sensor of claim 1, further comprising a double sampling element, receiving a first value indicative of a total charge, and a second value indicative of a reset level.

7. The sensor of claim 6, wherein said first value comprises a photosignal level, and said second value comprises a level after said flooding and spilling.

8. A method of operating an active pixel sensor comprising:

flooding at least one photosensitive part which at least includes a photodiode with excess charge;

allowing said at least one part to spill to a predetermined level of charge;

accumulating photoconductors in the photodiode;

transferring said photoconductors to the floating diffusion; and

sampling at least two levels from the floating diffusion representing sample and reset levels, to determine an amount of light.

9. A method as in claim 8, further comprising shuttering said photodiode by using a gate which has a lower potential than a potential that a potential used for said transferring.

10. A method as in claim 8, wherein said transferring comprises biasing a gate at a level that allows incoming charge on the photodiode to trickle into the floating diffusion.

11. An active pixel sensor, having a plurality of pixels, each pixel comprising:

a photodiode, located to receive incoming light;

a photodiode precharge transistor, connected between the photodiode, and a source of precharge;

a floating diffusion, which, in operation, is isolated to allow said floating diffusion to accumulate charge;

a transfer gate, coupled between said photodiode and said floating diffusion;

a floating diffusion precharge transistor, selectively controlled to precharge said floating diffusion to a level of a source of precharge; and

an in-pixel buffer, connected as a follower, and having its input node connected to said floating diffusion and its output node connected to an output line.