Image sensors with adaptive filtering for row noise mitigation
An image sensor may include adaptive filtering circuitry that is used to correct for row noise. In one example, the image sensor may include a single reference pixel or a column of reference pixels that are shielded from incident light. The adaptive filtering circuitry may estimate row noise based on data from the reference pixel(s). Row noise correction circuitry may then subtract the estimated row noise from imaging pixel outputs to correct for row noise. If the row noise is dominated by supply noise, the reference pixels may be omitted entirely and the adaptive filtering circuitry may estimate row noise based only on the power supply voltage. The adaptive filtering circuitry may undergo a training phase to optimize coefficients for the adaptive filtering circuitry.
1. An image sensor comprising:
an array of imaging pixels;
at least one reference pixel that is shielded from incident light;
adaptive filtering circuitry configured to receive data from the at least one reference pixel, wherein the adaptive filtering circuitry is configured to:
undergo a training phase during a calibration frame for coefficients of an adaptive filter; and
use the coefficients during subsequent imaging frames to provide outputs that represent row noise estimates; and
row noise correction circuitry configured to correct pixel values from the array of imaging pixels based on the outputs from the adaptive filtering circuitry.
2. The image sensor defined in claim 1 , wherein undergoing the training phase for the coefficients of the adaptive filter comprises undergoing the training phase for the coefficients of the adaptive filter according to a least mean squares algorithm.
3. The image sensor defined in claim 1 , wherein undergoing the training phase for the coefficients of the adaptive filter comprises undergoing the training phase for the coefficients of the adaptive filter according to a recursive least squares algorithm.
4. The image sensor defined in claim 1 , wherein the adaptive filtering circuitry is configured to provide the outputs that represent row noise estimates based on data from a single reference pixel.
5. The image sensor defined in claim 1 , wherein the adaptive filtering circuitry is configured to provide the outputs that represent row noise estimates based on data from multiple reference pixels.
6. The image sensor defined in claim 5 , wherein the adaptive filtering circuitry is configured to provide the outputs that represent row noise estimates based on an average of respective outputs from the multiple reference pixels.
7. The image sensor defined in claim 1 , wherein the at least one reference pixel includes no more than a single reference pixel.
8. The image sensor defined in claim 1 , wherein the at least one reference pixel includes no more than a single column of reference pixels.
9. An image sensor comprising:
an array of imaging pixels;
at least one reference pixel that is shielded from incident light;
adaptive filtering circuitry configured to receive data from the at least one reference pixel, wherein the adaptive filtering circuitry is configured to undergo a training phase for coefficients of an adaptive filter according to a recursive least squares algorithm; and
row noise correction circuitry configured to correct pixel values from the array of imaging pixels based on an output from the adaptive filtering circuitry.
10. The image sensor defined in claim 9 , wherein the output is an estimate of row noise.
11. The image sensor defined in claim 10 , wherein the adaptive filtering circuitry provides the estimate of row noise based on data from a single reference pixel.
12. The image sensor defined in claim 10 , wherein the adaptive filtering circuitry provides the estimate of row noise based on data from multiple reference pixels.
13. The image sensor defined in claim 12 , wherein the adaptive filtering circuitry provides the estimate of row noise based on an average of respective outputs from the multiple reference pixels.
14. The image sensor defined in claim 9 , wherein the at least one reference pixel includes no more than a single reference pixel.
15. The image sensor defined in claim 9 , wherein the at least one reference pixel includes no more than a single column of reference pixels.