Compensation of Signal-Dependent Readout Noise in Photon Transfer Curve Characterisation of CMOS Image Sensors

Abstract

The signal independence of the noise induced by the analogue signal processing chain in CMOS imagers is important for measurement accuracy when applying the photon transfer technique. This brief shows the implications of signal-dependent readout noise on the photon transfer method, and proposes a methodology to minimize its sensitivity to cameras with non-flat electronic readout noise. This noise can in some cases be signal-dependent, which alters the Photon Transfer Curve (PTC) used for evaluating photodiode array performance. A modulated PTC changes the imager transfer constant, which could lead to inaccurate parameter calculations. We reveal that the typical application of single-point calculation for the sense node to ADC sensitivity constant near the full well diode capacity is insufficient. This brief proposes a methodology for compensation of signal-dependent readout noise using multi-point measurements in the low-light segment of the PTC curve, which improves control over calculations using the PTC method.