Method and device for reading a pixel

1. A method for reading a pixel, the method comprises:

generating a first signal responsive to light sensed by the pixel during a first exposure period;

writing a second value to the pixel by utilizing an analog feedback circuit that comprises an analog memory cell; wherein the second value is responsive to a value of the first signal, to an analog writing process threshold that is characteristic of the writing and to a first threshold;

generating a third signal responsive to the second value and to light sensed by the pixel during a second exposure period;

reading a third value of the third signal;

writing a fourth value to the pixel by utilizing the analog feedback circuit; wherein the fourth value is responsive to third value, to the analog writing process threshold and to the first threshold;

reading the fourth value; and

calculating a digital detection signal in response to the third value and in response to the fourth value; wherein the first threshold does not exceed a product of a full well value multiplied by a ratio between a length of the first exposure period and an aggregate length of the first and second exposure periods.

2. The method according to claim 1 wherein the stage of writing the second value comprises:

writing the first value to an analog memory cell;

reading the first value from the analog memory cell; and

writing the second value to the pixel.

3. The method according to claim 1 wherein the calculating comprises defining the digital detection signal as a maximal value out of: (i) a sum of the third and fourth values; and (ii) a product of: (a) a difference between the third value and the fourth value, and (b) a timing coefficient representative of a relationship between an aggregate length of the first and second exposure periods and a length of the second exposure period.

4. The method according to claim 1 wherein multiple pixels are arranged in a two dimensional array of pixels; wherein pixel column is coupled to a single analog memory cell; wherein multiple digital detection signals are calculated in parallel for multiple pixels that form a row of pixels; and wherein multiple detection signals are calculated in a serial manner for pixels that form a pixel column.

5. A device, comprising a pixel, a readout circuit and an analog feedback circuit; wherein the analog feedback circuit comprises an analog memory cell;

wherein the pixel generates a first signal responsive to light sensed by the pixel during a first exposure period;

wherein the analog feedback circuit writes a second value to the pixel; wherein the second value is responsive to a first value of the first signal, to an analog writing process threshold that is characteristic of a writing of the second value and to a first threshold;

wherein the pixel generates a third signal responsive to the second value and to light sensed by the pixel during a second exposure period;

wherein the readout circuit reads a third value of the third signal;

wherein the analog feedback circuits writes a fourth value to the pixel; wherein the fourth value is responsive to the third value, to the analog writing process threshold and to the first threshold;

wherein the readout circuits reads the fourth value; and

wherein a calculator coupled to the readout circuit calculates a digital detection signal in response to the third value and to the fourth value; wherein the first threshold does not exceed a product of a full well value multiplied by a ratio between a length of the first exposure period and an aggregate length of the first and second exposure periods.

6. The device according to claim 5 wherein the analog memory cell stores the first value and wherein the first value is clipped during a write operation to the pixel.

7. The device according to claim 5 wherein the calculator is adapted to define the digital detection signal as a maximal value out of: (i) a sum of the third and fourth values; and (ii) a product of: (a) a difference between the third value and the fourth value, and (b) a timing coefficient representative of a relationship between an aggregate length of the first and second exposure periods and a length of the second exposure period.

8. The device according to claim 5 comprising multiple pixels that are arranged in a two dimensional array of pixels; wherein pixel column is coupled to a single analog memory cell; wherein the calculator calculates multiple digital detection signals in parallel for multiple pixels that form a row of pixels; and wherein the calculator calculates in a serial manner multiple detection signals for pixels that form a pixel column.

9. The method according to claim 4 , comprising sending an anti-blooming signal of a value that is proximate to the full well value to all of the multiple pixels.