A 280-μ V Temporal Noise, 76-dB Dynamic Range CMOS Image Sensor With an In-Pixel Chopping-Based Low-Frequency Noise Reduction Technique

In this article, a low-noise CMOS image sensor with enhanced dynamic range (DR), using an in-pixel chopping technique, is presented. The proposed in-pixel chopping reduces the low frequency or 1/ ${f}$ noise of the source follower (SF) in an active pixel sensor (APS), which is a major component of the temporal noise. A conventional 3T active pixel, with an n-well/p-sub photodiode (PD), is modified to implement a chopper inside a pixel using only one additional switch. The minimum-sized nMOS transistor acting as a switch is used without much compromising the fill factor (FF). A prototype sensor, with a $128 \times 128$ pixel array, is fabricated in an Austria Micro Systems (AMSs) 0.35- $\mu \text{m}$ CMOS OPTO process. The pixel pitch is 10.5 $\mu \text{m}$ with an FF of $30{\%}$ . The measured temporal noise is $280 \mu V_{\textbf {rms}}$ at the chopping frequency ( $\boldsymbol {f}_{\textbf {ch}}$ ) of 8 MHz, which shows a reduction in the noise power by 11 dB when compared to a conventional 3T pixel. The reduced noise floor enhances the DR of the pixel from 65 to 76 dB.