Offset-free offset correction for active pixel sensors

We describe a method to improve the reading of active pixels, so that this FPN is cancelled, with as final result a better cosmetic quality of the image. Several solutions to this problem have been proposed in literature. We described a technique based upon shifting the threshold voltage of the source follower transistor in the pixel [1] and a correction technique with a dedicated co-processor [2]. The solution proposed here is a correlated double sampling technique, which is a widespread technique to tackle this problem for integrating pixels [3, 4, 5].