A 2erms− Temporal Noise CMOS Image Sensor With In-Pixel 1/f Noise Reduction and Conversion Gain Modulation for Low Light Imaging.

This work presents a low noise active pixel sensor. It uses one additional transistor compared to standard 4T pixel to obtain 1/f noise reduction and high conversion gain. 1/f noise is reduced by periodically switching the in-pixel source follower between depletion and inversion. The depletion state is achieved by re-configuring the source follower into a MOS capacitor and depleting the channel by controlling the source-drain terminal. The state change of the in-pixel source follower also enhances the conversion gain. The test chip has a $64 \times 64$ pixel array with a $10~ {\mu }\text{m}$ pixel pitch fabricated in 350 nm AMS process. The measured integrated noise of a pixel in the frequency band 128 Hz to 50 KHz is $728~ {\mu V_{rms}}$ without switching. At a switching frequency of 4 MHz, the integrated noise reduces to $306~ {\mu V_{rms}}$ after switching resulting in a 7.5 dB reduction. The input referred noise is reduced from $26 {e_{rms}^{-}}$ to $7.3 {e_{rms}^{-}}$ after applying switching. When both, switching and conversion gain enhancement are applied, the input referred noise is further reduced to $2.3 {e_{rms}^{-}}$ with an enhanced conversion gain of $398\,\, {\mu V/e^{-}}$. [ABSTRACT FROM AUTHOR]