On-Chip FPN Calibration for a Linear-Logarithmic APS Using Two-Step Charge Transfer

This paper proposes a novel fixed pattern noise (FPN) calibration technique for a linear-logarithmic active pixel sensor (APS) based on the conventional four-transistor pixel structure. The offset FPN originated from the threshold characteristic variation of the transfer gate is calibrated with the proposed two-step charge transfer method, without any modification of the pixel structure or image-processing steps. The prototype sensor is fabricated by using a 0.13-mu m CMOS image sensor process. The chip includes a 320 x 240 pixel array with a 2.25 mu m pixel pitch and the peripheral circuitry. A wide dynamic range of more than 105 dB has been achieved from the proposed operation mode while maintaining the offset FPN less than 0.58% over the entire dynamic range.