Charged coupled device
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Transcript of Charged coupled device
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Charged Coupled Device
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Contents
Introduction
Readout Process
Image Scanning
Image Generation
Final Procedure
Aspects of CCD Behavior
Advantages
Disadvantages
Applications
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Introduction
• A Charge Coupled Device (CCD) is a highly sensitive photon detector.
• CCDs are dynamic devices that move charge along a predetermined paths under control of clock pulses.
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How CCD is clocked out?
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• The upper section shows charge being collected under one of the electrodes. To transfer the charge out of the CCD, a new potential well can be created by holding IØ3 high, the charge is now shared between IØ2 and IØ3 (section 2).
• If IØ2 is now taken low, the charge will be fully transferred under electrode IØ3 (section 3).
• To continue clocking out the CCD, taking IØ1 high and then taking IØ3 low will ensure that the charge cloud now drifts across under the IØ1 electrodes.
• As this process is continued, the charge cloud will progress either down the column, or across the row, depending upon the orientation of the electrodes.
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Image Scanning
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.
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Image Generation
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Final Procedure
• The final process on the CCD is the reading of each pixel so that the size of the associated charge cloud can be measured.
• The CCD is an analogue device, and the analogue voltage values are converted into a digital form by the camera electronics.
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Aspects of CCD Behavior
1. Quantum Efficiency
2. Wavelength Range
3. Dynamic Range
4. Linearity
5. Noise
6. Power
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Advantages
• Relative simple
• More sensitive than photographic film
• Cheaper to replace if failure
• Modularity-easy upgrades
• Detector costs simple
• No chemical processing is needed
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Disadvantages
• Demagnification is a major issue
• Vary with application
• Very expensive
• Relates to potentially lower DQE
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Applications
• Astronomical Imaging
• Infrared Detection and imaging
• Signal Processing
• Digital Photography
• Medical Fluoroscopy
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CCD Chip
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References http://www.mssl.ucl.ac.uk/www_detector/ccdgroup/optheor
y/ccdoperation.html
http://www.microscopyu.com/articles/digitalimaging/ccdintro.html
http://micro.magnet.fsu.edu/primer/digitalimaging/concepts/threephase.html
http://www.sciencedirect.com/science/article/pii/0026271476906065
https://www.noao.edu/meetings/gdw/files/Howell_CCDs.pdf
http://www.science20.com/mei/blog/charge_coupled_device_ccd
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Thank you