CMOS image sensor with shared in-pixel amplifier and calibration facility

A CMOS image sensor is presented which uses a feedback loop to keep the reverse bias voltage of the photo diode on a constant value in order to reduce the dark current. In order to preserve pixel cell area the amplifier required in the feedback loop is located partly in the pixel cell and partly in the readout circuit. The sensor has an on-chip calibration facility, the resulting fixed pattern noise is less than 0.02%. When operated in voltage mode it has a logarithmic response, but it can also be operated in current mode where it shows linear behavior. The proposed pixel cell has been implemented in a 0.6 μm CMOS technology. With its size of (15 × 15)μm² it is only slightly larger than a standard integrating pixel cell with approximately the same photosensitivity while having approximately the same power dissipation. The fill factor is about 27%. The pixel cell is suited for video rate operation (50 fps) in image sensor arrays with moderate resolution.