Biomedical Engineering Reference
In-Depth Information
Dried-bR photoreceptors are inherently susceptible to electrical noise because of their
extremely high film resistance. Moreover, photoinduced currents flowing through the bR
photoreceptor are very small. Measuring such small signals requires circuitry that is
highly insensitive to noise. Fabricating switched integrator circuitry on a standard PCB
board using discrete surface-mount components is impractical for precision low-noise
applications. The most significant problem is switching noise, which is caused by charge
injection across the parasitic capacitances of FET switches. To reduce the overall noise, it
is recommended that the switched integrator with correlated double sampling circuitry be
combined into a single-chip design.
The 4
4 photoreceptor prototype is provided as a proof of concept. Designing it in this
manner imposes some limitations, such as limited spatial resolution and excessive physi-
cal size. Creating high-resolution motion detectors requires reducing the pixel scale and
improving the readout architecture. Unfortunately, as photosensitive areas decrease in size
and complex processing circuitry consume larger areas, the limitations of 2D architectures
become evermore apparent. Extending the array architectures to 3D provides a promising
solution to this conflict. By arranging the photoreceptor, amplifier, and motion circuitry in
layers, maximum utilization of sensor area can be achieved. Continuing innovation in
thin-film transistor technology may provide a means to realize practical and flexible bR
photoreceptor imaging devices.
Acknowledgments
This work has been supported by research grants to Professors A.S. Bassi and G.K. Knopf
from the Natural Sciences and Engineering Research Council of Canada (NSERC), the
Canada Foundation for Innovation (CFI), and Photonics Research Ontario (PRO). The
authors would like to thank Nicholas Jankovic, Qing Zhang, Gerrit Aartsen, and Eugen
Porter for their constant assistance and valuable discussions.
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