Exposure control in electronic cameras by detecting overflow from active pixels

• US 6,833,871 B1
• Filed: 07/16/2001
• Issued: 12/21/2004
• Est. Priority Date: 02/26/1998
• Status: Expired due to Term

• Current Assignee: Foveon, Inc. (Avis Budget Group Incorporated)
• Original Assignee: Foveon, Inc. (Avis Budget Group Incorporated)
• Inventors: Merrill, Richard B., Lyon, Richard F., Mead, Carver A.
• Primary Examiner(s): Vu, Ngoc-Yen, Vu, Ngoc-Yen
• Assistant Examiner(s): Solomon, Gary L
• Application Number:
  US09/872,070
• Time in Patent Office: 1,254 Days
• Field of Search: 348/302, 348/294, 348/308, 348/296, 348/297, 348/288, 348/299, 348/241, 348/243, 257/223, 250/208.1
• US Class Current: 348/302
• CPC Class Codes: H04N 25/53 Control of the integration time
• CPC Class Codes: H04N 25/587 acquired sequentially, e.g. using the combination of odd and even image fields
• CPC Class Codes: H04N 25/59 by controlling the amount of charge storable in the pixel, e.g. modification of the charge conversion ratio of the floating node capacitance
• CPC Class Codes: H04N 25/623 by evacuation via the output or reset lines
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/67 applied to fixed-pattern noise, e.g. non-uniformity of response
• CPC Class Codes: H04N 25/771 comprising storage means other than floating diffusion

Abstract

A method for controlling the exposure of an active pixel array electronic still camera includes the steps of: integrating photocurrent in each pixel during an integration time period; collecting overflow charge from all pixels in the array during the integration time period; developing an overflow signal as a function of the overflow charge; and terminating the integration time period when the overflow signal exceeds a preset threshold level selected to represent a desired reference exposure level. Apparatus for performing the method of the present invention includes circuitry for integrating photocurrent in each pixel during a integration time period; circuitry for diverting and detecting overflow charge from all pixels in the array during the integration time period; circuitry for developing an overflow signal as a function of the overflow charge; and circuitry for terminating said integration time period when the overflow signal exceeds a preset threshold level selected to represent a desired reference exposure level.

Claims

1. A method for controlling the exposure of an active pixel array disposed on a semiconductor substrate, comprising the steps of:

adjusting a charge barrier in each said pixel to a first overflow level;

integrating photocurrent in each said pixel during a first integration time period while said charge barrier is set at said first overflow level;

collecting overflow charge from all said pixels in said array during said first integration time period;

developing an overflow signal;

adjusting said charge barrier for each said pixel to a second overflow level when said overflow signal exceeds a predetermined threshold;

determining a duration for a second integration time period;

integrating photocurrent in each said pixel during said second integration time period while said charge barrier is set at said second overflow level; and

terminating said second integration time period after said determined duration.

2. A method for controlling the exposure of an active pixel array disposed on a semiconductor substrate, comprising the steps of:

resetting each pixel during a reset time period;

adjusting a charge barrier in each said pixel to a first overflow level;

integrating photocurrent in each said pixel during a first integration time period while said charge barrier is set at said first overflow level;

collecting overflow charge from all said pixels in said array during said first integration time period;

developing an overflow signal;

adjusting said charge barrier for each said pixel to a second overflow level when said overflow signal exceeds a predetermined threshold;

determining a duration for a second integration time period;

integrating photocurrent in each said pixel during said second integration time period while said charge barrier is set at said second overflow level; and

terminating said second integration time period after said determined duration.

3. An apparatus for controlling the exposure of an active pixel array, comprising:

means for adjusting a charge barrier in each pixel to a first overflow level;

means for integrating photocurrent in each said pixel during a first integration time period while said charge barrier is set at said first overflow level;

means for collecting overflow charge from all said pixels in said array during said first integration period;

means for developing an overflow signal;

means for adjusting said charge barrier for each said pixel to a second overflow level when said overflow signal exceeds a predetermined threshold;

means for determining a duration for a second integration time period;

means for integrating photocurrent in each said pixel during said second integration time period while said charge barrier is set at said second overflow level; and

means for terminating said second integration time period after said determined duration.