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  1. Charge Coupled Devices ( ( CCD • Ahmed Ashraf • Aya Mohamed • Alaa Mohamed
  2. What is a charge-coupled device (CCD)? • It can be defined as a light-sensitive integrated circuit imprinted on a silicon surface to form light-sensitive elements called pixels, and each pixel is converted into an electrical charge • It can be treated as CCD sensor, which is used in the digital and video cameras for taking images and recording videos through photoelectric effect. It is used for converting the captured light into digital data, which is recorded by the camera.
  3. CCD
  4. CCD OPERATION • They transfer incoming photons into an electrical charge in the CCD chip • The photons are received in a photoactive region of silicon • A lens is used to focus the light onto the silicon • A charge is accumulated in the capacitors proportional to the light intensity • Each photo site corresponds to an individual pixel in the finial image and photo sites are often referred to simply as pixels • Each “photo sites” will refer to the CCD chip and “pixels” will refer to an image.
  5. • When a photon of light strikes the surface of certain metal materials the energy imparted by the photon can release an electron from the metal • in a CCD , this electron is stored within the walls of a photo site • Basically, the camera turns light into electricity. A CCD camera forms light sensitive elements called pixels which sit next to each other and form a particular image. CCD cameras have been in production for a long period of time and tend to have high quality pixels that produce a higher quality, low-noise image than any other camera. CCD OPERATION
  6. Applications • CCDs are used in digital cameras , optical scanner s and video cameras as light- sensing devices . • CCD cameras used in astrophotography . • CCDs are typically sensitive to infrared light, which allows infrared photography, night-vision devices, and zero lux (or near zero lux) video-recording/photography. • CCD are use to take exposures of galaxies and nebulae .
  7. CCD Camera The CCD camera consist of three main parts : 1. Camera Body • the camera body is the mechanical part of the camera and it houses the CCD chip and protects it against unwanted light from outside. 2. CCD Chip • A CCD chip is a light sensitive device made of silicon. its an array of light sensitive pixels , it will be converted to a charge , this charge is captured in the pixel . it can't go to other pixels • the amount of charge is measure of the amount of light that felt on the pixel
  8. CCD Camera 3. Electronics • the electronics of the camera are the intermediate between the CCD chip and the computer • the computer must be able to control the camera through its electronics • to shift the lines on the CCD chip ,it needs clock signals or pulses that must be generated by the electronics or by the computer • another important task is the conversion of the analog output signal of the charge detection node to a digital format the computer is also to read.
  9. CCD Camera
  10. How a CCD chip registers image? • The telescope projects an image on the CCD chip. High intensity areas will produce more charge in the pixels than low intensity areas. • The amount of charge in every pixel makes the image,The computer can read this charge and convert it to an image. • The value in every pixel gives the charge, which is related to the light intensity.
  11. How is an image made with a CCD chip? There are three main phases: • Clearing phase • Exposure or integration phase • Readout phase
  12. Clearing phase • Mostly you don’t have a shutter in your camera, this means that there is always light falling on the CCD chip. • When you want to make an image, all existing charge has to be removed from the pixels.The CCD chip can shift lines downward with electrical pulses • All charge in a line will move to the line below of it.This happens with all lines of the chip on the same moment. • The lowest line will move the charge to a clearing line, where it will be removed. • When all lines are shifted away, there is no charge left anymore.This phase takes a few ms.
  13. Exposure or integration phase • The telescope projects the image on the CCD chip, so charge will accumulate in the pixels. • The longer you wait, the more light will be registered by the chip. • This phase controls the exposure time, also called: integration time, • because the chip integrates the amount of light in a certain period.With lunar and planetary photography it usually takes a few tenths of a second, but it can take minutes or even hours
  14. Readout phase • To get the image in your computer, it will have to read the amount of charge of every pixel. • There is a device, the charge detection node , in the CCD chip that is able to measure the charge of a pixel. • Every pixel must be shifted in this device.The lowest line is able to shift pixels to the left in the direction of the device. So these pixels can be measured one by one. • When all pixels of the line are measured, all lines are shifted one line down. • Then again the lowest line can be measured.This will be repeated until all lines are measured. • he computer can read the measurements through the camera electronics.This phase can take a few seconds.
  15. The most used types of CCD chips •frame device This is the most simple device. It is used in the CB211 camera.This type can’t be used with lunar and planetary photography without a shutter. Making images of this kind of objects typically requires an integration time of a few tenths of a second.The problem is the readout time, which can take a few seconds. During readout, the chip is still receiving light, which will destroy the original image, before it’s completely read by the computer.
  16. •Frame transfer device With this kind of chip, the lowest half of the chip is protected against light.The image is only made on the upper half of the chip. When you are finished making your image, the image will be transferred from the upper half to the lower half, where it will be protected from light.This will take only a few ms.There is enough time, in this area, to read the image. A frame transfer device can be used with lunar and planetary photography. The most used types of CCD chips
  17. •Interline transfer device One line of every two lines is protected from light. During integration, only one line receives light. At the end, this line is shifted to the protected line, where it will be read by the computer. An interline transfer device can be used with planetary photography, Lunar photography will be more difficult, because of it’s brightness.The bright light can influence the protected line.The protected area of a frame transfer device is safer. The most used types of CCD chips
  18. Advantages • Relative simple • More sensitive than photographic film • Cheaper to replace if failure • Modularity- easy upgrades • Detector costs simple • No chemical processing is needed
  19. Disadvantages • CCD sensors consume much more power • HD video- less pixel rates. • CCDS are expensive as they require special manufacturing. • CCD sensors may be wired/wireless- mastering the use requires some effort and learning period