Polarization Sensitive Current-Mode Sensor

Vision Systems Design: Proceeedings of the IEEE publishes an open-access invited paper "Bioinspired Polarization Imaging Sensors: From Circuits and Optics to Signal Processing Algorithms and Biomedical Applications" by Timothy York, Samuel B. Powell, Shengkui Gao, Lindsey Kahan, Tauseef Charanya, Debajit Saha, Nicholas W. Roberts, Thomas W. Cronin, Justin Marshall, Samuel Achilefu, Spencer P. Lake, Baranidharan Raman, and Viktor Gruev.

The paper proposes to use polarization imaging to detect cancer cells. For unknown reasons, the pixel is current-mode based:

Current-mode pixel schematic and peripheral readout circuitry of the imaging sensor. The pixel’s readout transistor operates in the linear mode, allowing for high linearity between incident photons on the photodiode and output current from the pixel.

Cross section of the pinned photodiode together with the reset,
transfer, readout, and select transistors. The diode is an n-type diode
on a p-substrate with an insulating barrier between. The readout
transistor operates as a transconductor, providing a linear
relationship between accumulated photo charges and an
output current.

The 7.4um-sized pixel in 180nm process shows excellent PRNU of less than 0.1% rms, in spite of Gm variations between the pixels:

Histogram of all responses of pixels in the imaging array to a uniform
illumination at room light intensity. The fixed pattern noise of the
current-mode imaging sensor