Analyzing and Simulating Low-light Nonlinearity in CMOS Image Sensors

13 February, 2024

With the number of analog to digital converters (ADC) increasing to read larger pixel arrays at higher frame rates, disturbances on shared nets can cause nonlinearity. Although traditional sources of nonlinearity are well-known — along with the techniques to correct them during post-processing — linearity degradation due to array effects can be more difficult to correct. Scene-dependent low-light nonlinearity is even more of a challenge, as the required corrections need to be modulated based on what may be happening elsewhere in the image.

With smaller routing pitch and a larger number of ADCs, array effects — which typically have a scene-dependent component — are an increasingly important source of nonlinearity. When using a single-slope ADC architecture, ADCs convert at the same time range for the same signal level, potentially causing crosstalk as an adverse array artifact. This crosstalk is more severe in low-light conditions since the shot noise is insignificant. In short, array effects can’t be masked.

Addressing these challenges, our new white paper explains mechanisms that can contribute to low-light integrated nonlinearity (INL) in CMOS sensor applications. It also offers some plausible solutions and describes a method to simulate low-light nonlinearity.

To learn more, download our white paper.