On Threshold Comparing Biomorphic Image Sensors

CMOS image sensors have become the principal image sensors for the vast majority of digital cameras currently in market. The market popular sensor is a typical linear sensor which can capture 3-4 decades of illumination intensity, compared to 6-7 decades captured by the human eye. This has inspired research into biomorphic image sensors for over two decades by various groups leading to a number of adaptive pixels, threshold comparing pixel with neurons like firing mechanism as well as logarithmic pixels utilizing sub-threshold transistors. However, these have met little commercial success, often due to higher temporal and fixed pattern noise as well as limited dynamic range. In the paper, we will present a different approach to threshold comparison pixels, wherein a monotonically increasing reference signal is compared to the photo generated charge. The value at which the two signals intersect is recorded as the pixel's response. The monotonically increasing reference signal can be changed at the pixel's operation to produce any transduction function from the pixel. The tone mapped reference signal can be used to produce tone mapped responses