UNIT 12
CCD Flat Panel Displays
A charge-coupled device (CCD) is a light-sensitive integrated circuit that stores and displays the data for an image in such a way that each pixel (picture element) in the image is converted into an electical charge whose intensity is related to a color in the color spectrum.
For a system supporting 65,535 colors, there are separate value for each color that can be stored and recovered.
CCDs are included in digital still and video cameras.
They are also used in astronomical telescopes, scanners, and bar code readers.
A flat panel display is a television that uses a thin panel design instead of a traditional cathode ray tube (CRT) design. These screens are much lighter and thinner, and can be much more portable than traditional televisions and monitors. They also have higher resolution than older models.
New flat panel displays utilize a liquid crystal display (LCD) display. This system lights up various pixels on the screen. The simple and small infrastructure allows extremely light and portable screens, which are popular for personal and business use. They also allow for bendable display screens.
There are two main technologies available in Digital Radiography: Charge Coupled Device (CCD) based detectors and Flat Panel (either direct or indirect capture) detectors.
The NOVA technology uses a very high density CCD (VHD CCD), a lens and a scintillator. Light from the scintillator is deflected by a mirror into the lens. The lens focuses light onto the 16 Megapixels of the CCD. A crucial difference between this and Flat Panel technology is NOVA’s VHD CCD based detector does not have any electronics in the radiation field.
Flat Panel systems - either direct or indirect - use a thin film transistor (TFT), layers that capture the X-ray generated electrons.
Unlike CCD technology, the electronics in Flat Panel systems are in the direct radiation beam which is damaging and can cause the electronics to fail. To protect the electronics and reduce the risk of failure, Flat Panel manufacturers “harden” them, a process which reduces the efficiency. Therefore, the maintenance cost of Flat Panel is very expensive. In contrast, NOVA detector protects its CCD sensor and sensitive electronics from any direct radiation of x-ray by design. Hence, it enjoys a much longer working life and easy maintenance.
Additionally, these devices have layers of components that are surrounded by protective casings. An arrays of smaller devices are tiled together which prevents an entirely seamless image.
Another important difference between CCD and Flat Panel technology pertains to fill factor. NOVA has 100% fill factor which means 100% of the pixel area is used. Flat Panel systems have far lower fill factors because they have electronics running through each pixel reducing the X-ray capture surface area. The higher the fill factor, the higher the resolution of the image and the lower the dose needed. NOVA’s 100% fill factor provides maximum efficiency with lower radiation.
References:
- Communication system by Bruce carison . TMH.
- Electronic Communication system by Kennedy IV Edition. TMH.
- Electronic Communication system by Roddey & Coolen, Pearson.
- Telecommunication system Engg. By Freeman John Wiley
- Communication system by Haykin,Wiley
