Color readout system for an active pixel image sensor

• US 6,233,013 B1
• Filed: 10/23/1997
• Issued: 05/15/2001
• Est. Priority Date: 10/23/1997
• Status: Expired due to Term

• Current Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Original Assignee: Xerox Corporation (Xerox Holdings Corp.)
• Inventors: Hosier, Paul A., Tandon, Jagdish C., Tewinkle, Scott L.
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): White, Mitchell
• Application Number:
  US08/956,613
• Time in Patent Office: 1,300 Days
• Field of Search: 348/303, 348/302, 348/272, 348/308, 348/314, 348/311, 348/307, 348/304, 257/440, 250/208.1
• US Class Current: 348/308
• CPC Class Codes: H04N 23/84 for processing colour signals
• CPC Class Codes: H04N 25/533 by using differing integration times for different sensor regions
• CPC Class Codes: H04N 25/534 depending on the spectral component
• CPC Class Codes: H04N 25/70 SSIS architectures; Circuits associated therewith
• CPC Class Codes: H04N 25/77 Pixel circuitry, e.g. memories, A/D converters, pixel amplifiers, shared circuits or shared components

Abstract

A full-color scanning array uses CMOS active pixel cells, or photogates, as photosensors. A set of photogates, each photogate being specifically filtered for one primary color, is associated with a common node. A clearing gate downstream of the common node applies a relatively high potential to a selected photogate, for the purpose of clearing any charge from the photogate. In this way, the integration time for the photogate can be started at a precise time, and the effective exposure time of each photogate can thereby be precisely controlled. Alternately, one of the set of photogates can be repeatedly cleared without a signal being read therefrom, allowing the array to operate in a monochrome mode.

Claims

1. A photosensitive apparatus comprising:

a first photogate, the first photogate creating a charge in response to light impinging thereon, and a first phototransfer gate associated with the first photogate, a charge in the first photogate spilling into the first phototransfer gate in response to an applied potential difference between the first photogate and the first phototransfer gate;

a second photogate, the second photogate creating a charge in response to light impinging thereon, and a second phototransfer gate associated with the second photogate, a charge in the second photogate spilling into the second phototransfer gate in response to an applied potential difference between the second photogate and the second phototransfer gate;

a common node associated with the first phototransfer gate and the second phototransfer gate, the common node being associated with an output line;

a reset gate disposed at a reset node on the output line, the reset gate adapted to selectably apply a predetermined reset potential to the reset node;

a clearing gate disposed on the output line between the common node and the reset node, the clearing gate being actuable to apply a predetermined potential on the common node, thereby clearing any charge on at least one of the first photogate or second photogate;

a transfer gate disposed in series on the output line between the clearing gate and the reset node, adapted to selectably transfer charge from one of the first photogate and the second photogate to the reset node; and

means for applying a predetermined transfer potential to a selected one of the first phototransfer gate and the second phototransfer gate simultaneously with actuating the clearing gate, thereby clearing charge on a selected one of the first photogate or second photogate and initiating an integration time for the selected one of the first photogate or second photogate, whereby the integration time of the first photogate can be controlled independently of the integration time of the second photogate.

5. The apparatus of claim 1, wherein the first photogate is sensitive to a first color, and the second photogate is sensitive to a second color.

2. In a photosensitive apparatus comprising:

a first photogate, the first photogate creating a charge in response to light impinging thereon, and a first phototransfer gate associated with the first photogate, a charge in the first photogate spilling into the first phototransfer gate in response to an applied potential difference between the first photogate and the first phototransfer gate;

a second photogate, the second photogate creating a charge in response to light impinging thereon, and a second phototransfer gate associated with the second photogate, a charge in the second photogate spilling into the second phototransfer gate in response to an applied potential difference between the second photogate and the second phototransfer gate;

a common node associated with the first phototransfer gate and the second phototransfer gate, the common node being associated with an output line;

a clearing gate disposed on the output line, the clearing gate being actuable to apply a predetermined potential on the common node; and

a transfer gate disposed in series on the output line between the clearing gate and the reset node, adapted to selectably transfer charge from one of the first photogate and the second photogate to the reset node,

a method of operating the apparatus, comprising the step of;

applying a predetermined transfer potential to a selected one of the first phototransfer gate and the second phototransfer gate simultaneously with actuating the clearing gate, thereby clearing charge on a selected one of the first photogate or second photogate and initiating an integration time for the selected one of the first photogate or second photogate, whereby the integration time of the first photogate can be controlled independently of the integration time of the second photogate.

3. The method of claim 2, further comprising the step of

applying a predetermined transfer potential to a selected one of the first phototransfer gate and the second phototransfer gate without actuating the clearing gate, thereby transferring charge on the selected one of the first photogate or second photogate to the output line and terminating the integration time for the selected one of the first photogate or second photogate.

4. The method of claim 2, further comprising the step of

always actuating the clearing gate when applying a predetermined transfer potential to the second phototransfer gate, thereby preventing transfer of charge form the second photogate to the output line.

6. The method of claim 2, wherein the first photogate is sensitive to a first color, and the second photogate is sensitive to a second color.