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Photon transfer (PT) is a valuable testing methodology employed in the design, operation, characterization, optimization, calibration, specification, and application of solid state imagers and camera systems (most notably CCD and CMOS). As far as the author knows, PT began its evolution during the era of vidicon tubes used by NASA's early planetary imaging missions. The noise floor for these imagers was typically constant with light level, although a slight noise elevation near saturation was occasionally observed. Researchers speculated that the noise increase was associated with photon shot noise and prepared rudimentary plots to graph the noise source and better understand its nature. These plots may have been the first photon transfer curves (PTCs) generated by an area array imager in which noise was plotted against signal.
In the mid-1970s the charge-coupled device (CCD) began to replace the vidicon to become the premier imager for NASA and the imaging world. This new solid state imager exhibited a read noise floor considerably lower than that of the vidicon (40 times less at that time). Photon shot noise was clearly observed, and the title âshot noise limitedâ was given to the sensor to signify its ideal performance. At the same time the CCD and PTC were immediately married. Although the formal name âphoton transfer curveâ would come a few years later, the new testing technique was formally born and would become an important measurement standard for the imaging community. Today PT is routinely used and continues to evolve along with the multitude of new imaging technologies in development.
The PT technique is applicable to all imaging disciplines. For example, CCD and CMOS solid state physicists as well as design and fabrication/process engineers rely on PT feedback to assist in the development and production of quality imagers. Table 1.1 lists key sensor performance parameters that are measured and optimized by PT and the chapters in this book where they are discussed.
Camera companies and their customers also regularly use a PTC for trouble shooting, characterization, optimization, and calibration purposes. The system level performance parameters listed in Table 1.2 depend on PT results.
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