Wide dynamic range linear-and-log active pixel

• US 7,733,382 B2
• Filed: 09/17/2008
• Issued: 06/08/2010
• Est. Priority Date: 08/23/2002
• Status: Expired due to Fees

• Current Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Original Assignee: Aptina Imaging Corporation (ON Semiconductor Corporation)
• Inventors: Takayanagi, Isao
• Primary Examiner(s): Tran; Sinh
• Assistant Examiner(s): Pasiewicz; Daniel M
• Application Number:
  US12/232,452
• Publication Number:
  US 20090051798A1
• Time in Patent Office: 629 Days
• Field of Search: 348/222.1, 348/223.1, 348/294, 348300-302, 348/308, 348/665, 257291-292, 382/167, 382/274
• US Class Current: 348/223.1
• CPC Class Codes: H04N 25/573 the logarithmic type
• 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 3/155 Control of the image-sensor operation, e.g. image processing within the image-sensor

Abstract

A pixel circuit having an improved dynamic range is disclosed. When incoming light detected by the photodiode is strong, the accumulated (integrated) charge on a signal capacitor becomes large. To compensate, the excess signal component becomes compressed and the pixel circuit begins operating in logarithmic rather than linear mode. In this way, the circuit can achieve a higher dynamic range more closely resembling the image sensing properties of the human eye.

Claims

1. A method of processing pixel signals comprising:

receiving a pixel signal from a pixel which linearly integrates charge during a period when collected charge is below a threshold value and which non-linearly integrates charge during a period when collected charge is above the threshold value;

separating the pixel signal into at least a color component and a brightness component;

processing the color component;

determining if a brightness level of the color component produced during the non-linear integration period is above or below a saturation threshold;

dividing the non-linearly charge integration period into a first phase and a second phase based on whether the brightness level is above or below the saturation threshold; and

recombining the processed color and brightness components for the first phase as the pixel output signal, and using the brightness component alone for the pixel output signal for the second phase.

2. The method of claim 1, wherein the act of processing comprises setting the color component value to zero.

3. The method of claim 1, wherein the act of processing comprises setting the color component value to a predetermined minimum value.

4. A method of processing a pixel signal of an imaging device comprising:

collecting photogenerated charge at a pixel of said imaging device during a charge integration period;

separating the collected charge into color and brightness components;

processing the color component linearly when the amount of collected charge is below a threshold level;

processing the color component logarithmically when the amount of collected charge is above the threshold level;

determining if a brightness level of the color component produced during the logarithmic processing is above or below a saturation threshold;

dividing the logarithmic charge processing into a first phase and a second phase based on whether the brightness level is above or below the saturation threshold; and

recombining the processed color and brightness components during the first phase as a pixel output signal, or using the brightness component alone during the second phase as the pixel output signal.

5. The method of claim 4, wherein either processing step comprises removing the color component.

6. The method of claim 4, wherein either processing step comprises changing the amount of collected charge of the color component to a predetermined minimum value.

7. A method of processing a pixel circuit signal comprising:

collecting photogenerated charge from a pixel circuit during a charge integration period;

collecting charge linearly when the amount of said collected charge is below a threshold value;

collecting charge logarithmically when said collected charge is above said threshold value;

prior to a pixel circuit reset operation, injecting charge into the collected charge;

separating said collected charge into color and brightness components;

processing said color component;

recombining said brightness and color components;

dividing said logarithmic charge-accumulation phase into first and second logarithmic phases corresponding to lower and higher saturation levels respectively; and

for said second logarithmic phase, setting a color signal from an output of said pixel to a predetermined value during the processing of said color component.

8. The method of claim 7, wherein the processing step comprises setting the value of the color component to zero.

9. The method of claim 7, wherein the processing step comprises removing the color component.

10. The method of claim 7, wherein the processing step comprises setting the value of the color component to a predetermined minimum value.