Temperature Effect on the Linearity Performance of a CMOS Image Sensor

This article focuses on the effect of the operating temperature of a CMOS image sensor (CIS) on the pixel performance, especially the linearity behavior. As the temperature increases, the value of the integration capacitor
C
_FD
in the floating diffusion (FD) region increases as well. Moreover, the gain of the in-pixel voltage buffer decreases. These two factors lead to a reduced value of the conversion gain. Due to an increase in the nonlinear part of the
C
_FD
, the linearity of the CIS at a higher temperature will deteriorate. A digital calibration method proposed previously is used to improve the linearity of the CIS. Measurement results conducted on a prototype image sensor, designed with a 0.18-
μ
m CIS technology, agree well with an updated analytical model of the CIS and demonstrate an efficient linearity improvement at different temperatures.