Post on 12-Oct-2015
description
CCD : Charge Coupled DeviceByM.C.Bansal,AEDDK JAIPUR
Nagar
What is CCDA transducer which converts optical image into electrical signalReads the image of picture by storing a group of charges based on the image Grabs light and color to transfer a visual image into a group of electrical charges, and then to screen or video tape.
CCD: Silicon SubstrateCCDs are made up of Silicon wafersEach wafer contains several chipsSelected chips are then cut from wafer & packaged for use in a system
CCD : Why Silicon Silicon is Sensitive to LightSuperb ability to Detect LightResponds to Visible wave length spectrum
CCD Sensor IC
Structure of a CCD
Resolution in CCD ICDepends on Number of Photo Sites on an Area with 3x4 aspect ratioExampleA color camera CCD (Panasonic WV-CD100) Use CCD Sensor YFVAKA0146AN 196,096 photo sites arranged in 512 vertical columns and 383 rowsSize of one Photo site (pixel or CCD element) is 26 microns by 22 microns
CCD BasicsCCD imaging performsExposure which converts light into electric charge at discrete photo sites called PixelsCharge Transfer, moves packet of Charge within silicon substrateCharge to Voltage conversion & Amplification
Construction of CCD (CCD Element)
Generation of charge on CCDNow V = 10 volts, free holes repelled deeper into the substrate a depletion layer is formed below the electrode When CCD Exposed to light photo electrons appears in inversion layerDepletion layer get reduced
Charge Coupling or Charge TransferConversion of charge packets takes place to voltage. Developed charge packets moves through the CCD device and delivered to output amplifier. In this Process
Charge CouplingStableeeeeeeeIf V2 more +ve than V1 the charge (e) moves to the new siteProcess continues until the whole charge image is routed to the output stageeeeeeee
Surface Trap : Smearing effectsurface channel CCDs
In Basic CCD element, the surface of the semiconductor where it meets the oxide layer has a tendency to trap electrons. This will not allow the complete transfer of charge and the charge packet will not be emptied completely to receive the next scan. These traps are called surface traps.
Buried Channel CCD
Charge transfer well below the surface to avoid surface traps.An extra layer of N type material below the oxide layerImprovement In S/N & Sensitivity
CCD FormatsPoint ScanningLine scanningArea Scanning
IT (Interline Transfer) Type CCDTransfer of charge
FT (Frame Transfer) Type CCDTransfer Of Charge DataFT device use shutter during the transfer of data from light receiving chip to storage section of chip at fast rate to reduce smear & shutter is synchronized with vertical blanking period.Not in use in most of the present day cameras because of larger size, problem due to use of shutter and problem of smear.
FIT (Frame Interline Transfer) Type CCD FIT type CCD consists of A light receiving CCD A vertical transfer CCD A storage CCD A horizontal transfer CCD
FIT (Frame Interline Transfer) CCD
During vertical blanking light image convert to charge image by the photo diode (CCD pixel) Transfer of chargeCharge is then transferred to the vertical transfer CCDResidual charge (smear) in CCD has been swept out via drain. Charges are transferred to storage CCD at high speed. Due to high speed of the charge transfer the smear due to light will be reduced.
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