CCD Detectors in High-Resolution Biology
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CCD Detectors in High-Resolution
BiologyJian Guan6-28-2013
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Overview• Some Chemistry Concepts• What is CCD?• How does CCD work?• Structure of CCD• Principle of CCD Operation• Pixel Size calculation
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Some Chemistry Concepts
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Silicon Crystal
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What is CCD?
Willard.S Boyle
George Elwood Smith
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How does CCD work?
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Structure of CCD
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Principles of CCD Operation
Direct detection,
well…
• More than enough
• Damage
• Interference from X-ray
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Strongelectro
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Indirect Detection is much more acceptable:Electron energy conversion into light
• high conversion efficiency into visible radiation,
• reasonably short and well-defined decay time of the emitted scintillation,
• phosphor output wavelength matched to CCD sensitivity (which has a maximum at ~700 nm),
• resistance to radiation damage,
• a convenient, reproducible method of depositing a thin layer of phosphor on a flat surface.
P20: zinc cadmium sulphide doped with silver
P43: gadolinium oxy-sulphide doped with terbium
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Optical coupling: Lens or Fibre optics
Lens coupling Fibre optics
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Readout and analog-to-digital
At the output Stage
The charge in Pixel is transferred to a capacitor
Amplifier and analog-to-digital converter
Convert charge to 12 bits or 16 bits resolution (Digitalization)
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Noises
• Dark current noise
• Readout noise
• Spurious events due to X-rays or cosmic rays
Temperature-dependent keep cold
Faster readout, more than one read out node
Software algorithm
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Electron diffraction applications
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Pixel Size CalculationCalculation of Pixel Size from a CCD Image
Pixel size = Actual pixel size
Magnification
Save CCD image in DM3 file format Get the pixel size information from the Digital Micrograph program
If not:
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Apogee AP7p CCDPixel Array: 512 x 512 pixelsArray Dimensions: 12.3 mm x 12.3 mmPixel Dimensions: 24 micron square
For Example
Actual pixel size = Array dimensionPixel arry = 12.3/512 = 24 micron
= 240,000 Angstrom
Magnification = 100,000
Pixel size = Actual pixel size
Magnification = 2.4 Angstrom
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