Abstract
The present invention provides an image sensor chip and a sensing method thereof. The image sensor chip includes pixel units. Each pixel unit includes a reset switch, a sampling switch, a light sensing element, a capacitor and an output circuit. The sampling switch is coupled between the reset switch and the light sensing element. The capacitor is coupled between the sampling switch and the output circuit. The output circuit outputs difference information corresponding to the difference between a plurality of sensing results of the light sensing element in different frame periods to a corresponding readout line. The sampling switch has a ON-time length in an exposure period and an OFF-time length in a readout and clean-up period. The ratio of the ON-time length to the OFF-time length is related to the ratio of the capacitance of the light sensing element to the capacitance of the capacitor.