A study on pixel circuit with compensation of background light using current mirror

Recently the image sensors for 3D range-finding system are employed widely and require the stability and reliability especially for mobile devices and automobiles in strong background light. Compared to strong background light, the intensity of the reflected light incident on the image sensor is very low, so environmental tolerance is required, and in particular, an image sensor not dependent on the background light is required. In this study, proposed 3-D range-finding system employs a modulated light with a specific frequency and two types of enhanced pixel circuits that are introduced for improvement of current error in current mirror. After the photocurrent by background light is duplicated using a current mirror, the pixel circuit can compensate the photocurrent by background light when signal light is accumulated. A test chip is fabricated in the LAPIS 0.18 mu m CIS process, and two types of the signal to background light ratio (SBR) in the simulation is -46.1 dB and -40.0 dB respectively.