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In this paper, a low-noise CMOS image sensor with enhanced dynamic range(DR), using an in-pixel chopping technique, is presented. The proposed in-pixelchopping technique is used to reduce the low-frequency or 1/f noise of thesource follower (SF) in an active pixel sensor (APS), which is a majorcomponent of the temporal noise. A conventional 3T active pixel, withn-well/p-sub photodiode (PD), is modified to implement a chopper inside apixel. A single minimum sized nMOS transistor is used in each pixel, withoutmuch compromising in the fill-factor (FF). Using chopping action thelow-frequency noise of the source follower is modulated to the choppingfrequency (f ch ) which is much higher than the maximum frequency of the inputsignal frequency band. The up-converted low-frequency noise is eliminated usinga column level low-pass filter (LPF), in the later stage. The reduction in thetemporal noise also results in an enhanced dynamic range of the image sensor.In addition, the readout consists of a column level high gain chopper amplifieralso reduces the non-linearity of the source follower. To validate the proposedtechnique a prototype sensor consists of a 128x128 sized pixel array within-pixel chopping and column level read-out circuitry, is fabricated in AMS0.35 {\mu}m CMOS OPTO process. The pixel pitch is 10.5 um (horizontal andvertical both) with a fill-factor of around 30%. The temporal noise is measuredas 280 uVrms at the chopping frequency (fch) of 8 MHz, which shows a reductionin the noise power by 11 dB. Due to the reduced noise floor, the dynamic rangeis enhanced from 65 dB to 76 dB, using the proposed technique.

Low-Frequency Noise Reduction Using In-Pixel Chopping To Enhance The Dynamic Range of a CMOS Image Sensor