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US 7,443,427 B2Granted
Wide dynamic range linear-and-log active pixel
AssigneeMicron Technology, Inc.
InventorIsao Takayanagi
Life of this patent
Estimating the term…
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.
Claims6
A method of operating a pixel circuit, comprising:
- collecting photogenerated charge at an integration node in response to a pixel signal during a charge integration period;
- operating a first transistors, in a shut-off mode, during said integration period when the amount of said collected charge is below a threshold value to cause charge to be linearly collected at said node;
- operating said first transistor, in a sub-threshold mode, during said integration period when said collected charge is above said threshold to cause charge to be logarithmically collected at said integration node;
- prior to a reset operation, injecting charge into a pixel capacitor coupled to said integration node;
- during the time said first transistor is operating in the sub-threshold mode, draining excess charge from said integration node through the first transistor;
- 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, eliminating a color signal from an output of said pixel during the processing of said color component.
8 more elements
A method of operating a pixel circuit, comprising:
- collecting photogenerated charge at an integration node in response to a pixel signal during a charge integration period;
- operating a first transistors, in a shut-off mode, during said integration period when the amount of said collected charge is below a threshold value to cause charge to be linearly collected at said node;
- operating said first transistor, in a sub-threshold mode, during said integration period when said collected charge is above said threshold to cause charge to be logarithmically collected at said integration node;
- prior to a reset operation, injecting charge into a pixel capacitor coupled to said integration node;
- during the time said first transistor is operating in the sub-threshold mode, draining excess charge from said integration node through the first transistor;
- 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 minimum value during the processing of said color component.
8 more elements
A method of operating a pixel circuit comprising:
- collecting photogenerated charge at an integration node in response to a pixel signal during a charge integration period;
- operating a first transistors, in a sub-threshold mode, during said integration period when said collected charge is above a threshold voltage of said first transistor to cause charge to be logarithmically collected at said integration node;
- dividing said logarithmic charge-collection phase into first and second logarithmic phases corresponding to lower and higher saturation levels respectively;
- and
- processing a signal representing said charge collected during said second logarithmic phase by setting a color signal to a predetermined minimum value.
2 more elements
Dependencies are inferred from the claim text.