![]() ![]() However, a major limitation is the need for a mechanical shutter (or a synchronized, short-duration light source called a strobe). This maximizes the number of pixels that can be included in a given area of silicon, and it also maximizes the portion of each pixel that is actually capable of converting photons into electrons. ![]() Thus, gate electrodes are made from transparent polysilicon.įull-frame CCDs are (relatively) straightforward and (relatively) easy to fabricate, and they allow the entire CCD surface to be light sensitive. In a full-frame CCD, we need to be able to apply these control voltages to regions that also function as photodetectors. After integration, the charge packets are moved vertically through the pixel locations toward the horizontal shift register.Īs we know from the previous article, we obtain CCD pixel data by applying carefully timed clock signals that sequentially create potential wells and potential barriers in the charge-transferring structure of the device. During integration, the pixel location accumulates electric charge in response to incident photons. I find it somehow counterintuitive that a semiconductor region could function as both a photoactive element and a charge-transfer device, but that’s exactly what happens in FF CCDs. In this article, we’ll examine the full-frame (FF), frame-transfer (FT), and interline-transfer (IT) CCD architectures. But these elements can be organized and implemented in different ways, and consequently “CCD” is a general image-sensor category that consists of several subcategories. The two most fundamental elements of any CCD image sensor are the photoactive area (such as a pinned photodiode) and the charge-transferring structures (i.e., horizontal and vertical shift registers). In the previous article, we looked at the general structure of CCDs at the semiconductor level. ![]()
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