Temperature Compensation Scheme for Logarithmic CMOS Image Sensor

ABSTRACT In this paper, we present a temperature compensation method for logarithmic CMOS image sensors. As Bandgap technique, the compensation circuit generates VPTAT1 and VPTAT2 voltages to compensate temperature variation of the sensor output signal voltage (Out-AC-Signal) which we call VCTAT1 and output reference voltage (VRef−ph) which we call VCTAT2. The proposed method is divided into three stages. At first, we copy the photocurrent in order to store it in the VPTAT1 circuit generator. Second, we use a pixel structure with improved output voltage swing. It has an output voltage swing two times larger than the standard logarithmic pixel. Third, we add a third column amplifier branch dedicated to VPTAT1 circuit generator. With this method, we obtain a good temperature stability of the sensor response in the temperature range from -30 to 125C without changing the sensor operation and we conserve all the same sensor response characteristics.