CHARGE COUPLED DEVICES

IN THIS PPT YOU CAN LEARNT WORKING OF CHARGE COUPLED DEVICES AND APPLICATION,TYPES

1. RAGHU ENGINEERING COLLEGE (AUTONOMOUS) DAKAMARRI M UDAY KUMAR 17981A04B8 ECE-C TECHNICAL SEMINAR ON CHARGE COUPLED DEVICES

2. OBJECTIVE Study and observe working and application of charged coupled devices

3. INTRODUCTION TO CCD’s CCDs are used to convert light into a digital value The CCD captures light and converts it to digital data that is recorded by the camera. 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.

4. TYPES OF CCD’S There are different CCDs such as Electron multiplying CCDs, Intensified CCD, Frame-transfer CCD Buried-channel CCD.

5. WORKING 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 final image and photo sites are often referred to simply as pixels.

6. Each “ photo sites ” will refer to the CCD chip and “pixels” will refer to an image. 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

7. HOW TO GET DATA FROM CCD’S Photo sites are read out, one row at a time, into a serial register along the bottom of the CCD array. The serial register then transfers the charge from each photo site to an output node. From there the charge is sent to the camera’s electronics unit where the electrons are digitized.

8. 8 CCDs can be used to collect an image in one of three ways, either one pixel at a time, one row at a time, or as an entire area at once.

9. How is an image made with a CCD chip? There are three main phases: Clearing phase Exposure or integration phase Readout phase 9

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 10 The value in every pixel gives the charge, which is related to the light intensity.

11. 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 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 11

12. Exposure or integration phase The lens 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

13. 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 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. The computer can read the measurements through the camera electronics 13

14. Applications CCDs are used in digital cameras, optical scanners 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 , video recording/photography. CCD are use to take exposures of galaxies and nebulae 14

15. Advantages Relative simple More sensitive than photographic film Cheaper to replace if failure Modularity-easy upgrades Detector costs simple No chemical processing is needed 15

16. DISADVANTAGES CCD sensors consume much 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

17. REFERENCE https://www.elprocus.com/know-about-the-working-principle-of-charge-coupled-device / https://en.wikipedia.org/wiki/Charge-coupled_device