| 摘要 |
<p>A photo sensor exhibiting low noise, low smear, low dark current and high dynamic range consists of a pinned (or buried) photodiode (PPD) with associated transfer gate (TG), a reset circuit (3) and a device (SL) with sub-linear voltage-to-current characteristic. The exposure cycle is started by reverse biasing the buried photodiode to its pinning potential and by setting the transfer gate (TG) to a non-zero skimming potential. Photo-generated charge carriers start to fill the buried photodiode; if illumination intensity is high, excessive photocharges are flowing over the transfer gate (TG) to the sensing node. Because of the sub-linear device (SL) connected to the sensing node, the voltage at the sensing node is a sub-linear function of the illumination intensity, and hence the dynamic range of the pixel is increased. The voltage at the sensing node (Se) is read four times, namely before exposure, with the spilled-over photocharge, after reset, and after the photocharge in the buried photodiode has been transferred to the sensing node. This allows correlated multiple sampling techniques to be employed for eliminating reset noise. Because of its compact size, the photo sensor can be employed in one- and two-dimensional image sensors fabricated with industry-standard CMOS or CCD technologies.</p> |
