Method and apparatus for calibrating imaging device circuits

1. A method of operating an imaging device comprising:

providing a linear stimulus to an imaging device to produce a calibration signal, the imaging device comprising an analog-to-digital converter which converts a representation of the calibration signal to a digital value;

sampling an output of the analog-to-digital converter;

determining correction values with a linearization circuit for a linear output based on the value of the linear stimulus and the sampled output of the analog-to-digital converter; and

storing the correction values in a storage circuit.

2. The method of claim 1 , further comprising:

receiving image data in the imaging device;

processing the image data through the analog-to-digital converter to produce digital values;

determining output values for the image data based on the digital values and the stored correction values; and

using the determined output values as the image data values.

3. The method of claim 2 , wherein determining output values comprises multiplying the processed image data with the stored correction values.

4. The method of claim 2 , wherein determining output values comprises substituting the processed image data with the stored correction values.

5. The method of claim 1 , wherein providing a linear stimulus comprises providing an electronic stimulus to the imaging device and to the linearization circuit.

6. The method of claim 5 , wherein providing an electronic stimulus comprises providing an output of a digital-to-analog converter to the imaging device and to the linearization circuit.

7. The method of claim 1 , wherein providing a linear stimulus comprises providing an optical stimulus to the imaging device and to the linearization circuit.

8. The method of claim 7 , wherein providing an optical stimulus comprises:

providing a reference detector for generating the calibration signal;

providing light to the reference detector and the imaging device; and

sampling an output of the reference detector to generate the calibration signal.

9. The method of claim 8 , wherein providing a reference detector comprises providing a light-receiving device having linear output characteristics.

10. The method of claim 8 , wherein providing a reference detector comprises providing a photo-conversion device.

11. The method of claim 10 , further comprising providing an amplifier coupled to the output of the photo-conversion device for generating the calibration signal.

12. The method of claim 1 , wherein the storage circuit comprises a look-up table.

13. An imaging device comprising:

a linear stimulus device for providing a calibration signal;

an analog chain adapted to receive the calibration signal from the linear stimulus device, the analog chain comprising a pixel and associated pixel readout circuitry;

an analog-to-digital converter coupled to the analog chain, the analog-to-digital converter converting a representation of the calibration signal to a digital value;

a linearization circuit adapted to receive an output from the analog-to-digital converter and the calibration signal from the linear stimulus device, the linearization circuit further adapted to determine correction values for linearizing the analog-to-digital converter output based on the analog-to-digital converter output and the calibration signal; and

a storage circuit adapted to receive and store the correction values from the linearization circuit.

14. The imaging device of claim 13 , wherein the correction values comprise multiplicative factors of the analog-to-digital converter output.

15. The imaging device of claim 13 , wherein the correction values comprise substitution values for the analog-to-digital converter output.

16. The imaging device of claim 13 , wherein:

the analog chain is further adapted to receive image data;

the analog-to-digital converter is further adapted to process the image data to produce digital values;

the linearization circuit is further adapted to:

determine corrected values for the image data based on the digital values and the stored correction values; and

use the determined output values as the image data values.

17. The imaging device of claim 16 , wherein the linearization circuit determines the corrected values by multiplying the processed image data with the stored correction values.

18. The imaging device of claim 16 , wherein the linearization circuit determines the corrected values by substituting the processed image data with the stored correction values.

19. The imaging device of claim 13 , wherein the linear stimulus device comprises an electronic stimulus device.

20. The imaging device of claim 19 , wherein the electronic stimulus device comprises a digital-to-analog converter coupled to the analog chain and to the linearization circuit.

21. The imaging device of claim 20 , wherein the pixel comprises:

a photo-conversion device;

a floating diffusion region for receiving and storing charge from the photo-conversion device;

a source follower transistor, the source follower transistor being coupled to the floating diffusion region;

a reset transistor, the reset transistor operable to reset the floating diffusion region to a predetermined reset voltage state; and

a row select transistor, the row select transistor acting as a switching device coupled to the source follower transistor,

wherein the digital-to-analog converter is coupled to the pixel.

22. The imaging device of claim 21 , wherein an output of the digital-to-analog converter is coupled to the floating diffusion region.

23. The imaging device of claim 21 , wherein an output of the digital-to-analog converter is coupled to an output terminal of the photo-conversion device.

24. The imaging device of claim 13 , wherein the storage circuit comprises a look-up table.

25. An imaging device comprising:

an optical linear stimulus device for providing a calibration signal;

an analog chain adapted to receive the calibration signal from the linear stimulus device, the analog chain comprising a pixel and associated pixel readout circuitry;

an analog-to-digital converter coupled to the analog chain, the analog-to-digital converter converting a representation of the calibration signal to a digital value;

a linearization circuit adapted to receive an output from the analog-to-digital converter and the calibration signal from the optical linear stimulus device, the linearization circuit further adapted to determine correction values for linearizing the analog-to-digital converter output based on the analog-to-digital converter output and the calibration signal; and

a storage circuit adapted to receive and store the correction values from the linearization circuit.

26. The imaging device of claim 25 , wherein the correction values comprise multiplicative factors of the analog-to-digital converter output.

27. The imaging device of claim 25 , wherein the correction values comprise substitution values for the analog-to-digital converter output.

28. The imaging device of claim 25 , wherein the optical linear stimulus comprises:

a reference detector comprising a light-receiving device having linear output characteristics; and

a light source.

29. The imaging device of claim 25 , wherein the storage circuit comprises a look-up table.

30. A camera system comprising:

a light source for providing a linear stimulus; and

an imaging device comprising:

a reference detector for providing a calibration signal;

an analog chain adapted to receive the calibration signal from the reference detector, the analog chain comprising a pixel and associated pixel readout circuitry;

an analog-to-digital converter coupled to the analog chain, the analog-to-digital converter converting a representation of the calibration signal to a digital value;

a linearization circuit adapted to receive an output from the analog-to-digital converter and the calibration signal from the reference detector, the linearization circuit further adapted to determine correction values for linearizing the analog-to-digital converter output based on the analog-to-digital converter output and the calibration signal; and

a storage circuit adapted to receive and store the correction values from the linearization circuit.

31. The camera system of claim 30 , wherein the correction values comprise multiplicative factors of the analog-to-digital converter output.

32. The camera system of claim 30 , wherein the correction values comprise substitution values for the analog-to-digital converter output.

33. The camera system of claim 30 , further comprising a lens assembly for receiving an image.

34. The camera system of claim 30 , further comprising a reflective surface for reflecting light from the light source to the reference detector.

35. The camera system of claim 30 , wherein the correction values comprise multiplicative factors of the analog-to-digital converter output.

36. The camera system of claim 30 , wherein the correction values comprise substitution values for the analog-to-digital converter output.

37. The imaging device of claim 30 , wherein the storage circuit comprises a look-up table.