IEEE Sensors publishes a video presentation of Xiaoliang Ge and Albert Theuwissen (Delft University) paper "A CMOS Image Sensor with Nearly Unity-Gain Source Follower and Optimized Column Amplifier."
"This paper presents a CMOS image sensor with in-pixel nearly unity-gain pMOS transistor based source followers and optimized column-parallel amplifiers. The prototype sensor has been fabricated in a 0.18 µm CMOS process. By eliminating the body effect of the source follower transistor, the voltage gain for the pixel-level readout circuitry approaches unity. The use of a single-ended common-source cascode amplifier with ground rail regulation improves the PSRR of the column-parallel analog front-end circuitry and further the noise performance. The prototype sensor with proposed readout architecture reaches a 1.1e- input-referred temporal noise with a column-level ×16 analog gain."
It seems only using the source-bulk connection, and nMOS can do the same thing. Does anybody compare the noise and PSR for the nMOS and pMOS source follower, which one gives the better performance?
ReplyDeleteThe original short paper can be found here:
ReplyDeletehttps://harvestimaging.com/pubdocs/211_IEEE%20Sensors%202016.pdf
It would have been interesting to see measurements of FPN / PRNU and linearity for this approach.
Newell capacitance lowers CG. Is it negligible?
ReplyDeleteIt is nice to see this video sharing here, even though the associated conference paper was published five years ago. Concerning the n-well cap, even this n-well introduces extra capacitance, the measured overall CG of pMOS w/o body-effect is still much higher than pMOS w/i body-effect. That is because the SF gain of the latter one is about 0.6, while the former one is around 1. I'm not sure if using the same approach with nMOS transistors is easy, as we have to have a separated p-well in the pixel. Regarding the linearity, my ex-colleague did a linearity analysis by using the same approach. From that measurement results, we see that the linearity of the proposed method is better than the one with a basic nMOS SF pixel. But the PRNU is worse. (F. Wang, A. J. P. Theuwissen, Pixel optimizations and digital calibration methods of a CMOS image sensor aimed for high linearity).
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