High dynamic range imaging sensor array
An apparatus having a rectangular imaging array characterized by a plurality of pixel sensors and a plurality of readout lines is disclosed. The apparatus has a plurality of column processing circuits, each column processing circuit being connected to a corresponding one of the readout lines and a plurality of signal injectors, one signal injector being connected to each of the readout lines. Each signal injector causes one of a predetermined number of voltages to be coupled to that readout line. An exposure for each of the pixel sensors is determined during image recording periods. The signal injectors inject a plurality of calibration voltages into the readout lines during calibration periods, and determines a gain function of an amplifier in one of the column processing circuits by measuring an output of the amplifier for the plurality of calibration voltages, the calibration period is between the imaging recording periods.
1. An apparatus comprising
a rectangular imaging array characterized by a plurality of pixel sensors and a plurality of readout lines;
a plurality of column processing circuits, each column processing circuit being connected to a corresponding one of said plurality of readout lines;
a plurality of signal injectors, one signal injector being connected to each of said readout lines, each signal injector causing one of a predetermined number of voltages to be coupled to that readout line; and
a controller that determines an exposure for each of said plurality of pixel sensors during each of a plurality of image recording periods, causes said signal injectors to inject a plurality of calibration voltages into said readout lines during each of a plurality of calibration periods, and determines a gain function of an amplifier in one of said plurality of column processing circuits by measuring an output of said amplifier during said plurality of calibration periods, said plurality of calibration periods being between said image recording periods.
2. The apparatus of claim 1 wherein said controller causes said signal injectors to inject a signal that has a value that a pixel sensor would generate if that pixel sensor was not exposed to light, said controller determining a column offset value for each of said plurality of column processing circuits.
3. The apparatus of claim 2 further comprising a plurality of rows of signal injectors, each column processing circuit being connected to a plurality of said signal injectors, said controller averaging said column offset values generated by said signal injectors in determining said column offset value.
4. The apparatus of claim 2 wherein said column offset value is determined during plurality of said calibration periods.
5. The apparatus of claim 1 wherein each of said plurality of pixel sensors comprises first and second photodiodes, said first photodiode being characterized by a different light conversion efficiency than said second photodiode.
6. The apparatus of claim 5 wherein said second photodiode has a light conversion efficiency less than 1/30th of said first photodiode.
7. The apparatus of claim 6 wherein said second photodiode comprises a parasitic photodiode that includes a floating diffusion node that is also used to convert a charge generated by said first photodiode to a voltage.
8. The apparatus of claim 5 wherein said controller determines a ratio of said first photodiode light conversion efficiency to said second photodiode light conversion efficiency during said plurality of image recording periods.
9. The apparatus of claim 8 wherein said controller determines said ratio by averaging signals from a plurality of pixel sensors in which said second photodiode generates a signal in a calibration range.
10. The apparatus of claim 9 wherein said calibration range excludes pixel sensors in which said second photodiode has a dark current greater than a dark current threshold.
11. The apparatus of claim 8 wherein said plurality of pixel sensors are divided into color channels, each color channel having a corresponding color filter over pixel sensors in that color channel, and wherein said controller determines said ratio separately for each of said color channels.
12. The apparatus of claim 5 wherein said first photodiode measures exposures between a first exposure and a second exposure and wherein said second photodiode can measure light exposure between a third exposure and a fourth exposure, said third exposure being less than said second exposure and said fourth exposure being greater than said second exposure.
13. The apparatus of claim 5 wherein said controller uses said first photodiode to measure exposures less than said second exposure and said second photodiode to measure exposures greater than said second exposure to simulate a single photodiode that can measure exposures between said first and fourth exposures.
14. The apparatus of claim 13 wherein said simulated single photodiode produces a first exposure value that is a linear function of said exposure and independent of said light conversion efficiencies of said first and second photodiodes and variations in said plurality of column processing circuits.
15. The apparatus of claim 14 wherein said first exposure value is characterized by a shot noise value and said controller outputs a second exposure value for each of said plurality of pixel sensors, said second exposure being determined by said first exposure value, said second exposure requiring fewer bits to output and differing from said first exposure by an amount that is less than said shot noise value.