Charge Coupled Device

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Charge Coupled Device

• M.Umar Javed

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Outlines

• Basics
• Photodiodes
• Photodiode Arrays
• Charge Coupled Device (CCD)
• History and Principle of working
• Characteristics
• Applications
• Advantages and Disadvantages
• References

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Photodiode

• A photodiode is a PN junction or
• PIN structure.

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Operation Modes

• Forward Bias

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• Reverse Bias

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Characteristics of PN Junction
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Photodiode Arrays

• A photodiode array is a linear array of discrete
  photodiodes on an integrated circuit chip.
• It works on the same principle as simple
  photovoltaic detector.

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• The photodiode array is a multichannel detector.
• They are useful in recording UV-Vis absorption
  spectra of samples.

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Charge Coupled Device (CCD)

• An instrument whose semiconductors are connected
  in such a way so that the output of one serves as
  the input of the next.

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• History
• The Charge Coupled Device was conceived
• in 1970 at Bell Labs by W.Boyle and G.Smith.
• Working Principle
• 1 Generate Charge ? Photoelectric Effect
• 2 Collect Charge ?Pixels (gates)
• 3 Transfer Charge ?Apply a differential voltage
  across gates. Signal electrons move down,
  vertical registers to horizontal register.
• 4 Detect Charge ?Individual charge packets are
  converted to an output voltage.

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The voltages supplied to the electrodes change,
and the electron packets move in response.
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CCD Characteristics

• Quantum Efficiency ()It is the ratio between
  photogenerated carriers to incident photons per
  pixel.

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Typical peak values

• Photographic plate 1-2
• Eye 1-2
• Photomultiplier tube20-30
• CCD 70-90
• (HgCdTe)30-50

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• Charge Transfer Efficiency (CTE)
• The fraction of electrons that are moved from
  one pixel to another during read-out is described
  by the charge transfer efficiency (CTE).
• Pixel to Pixel Variation
• This is fixed pattern noise because of the cell
  to cell non-uniformity.

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• Dynamic Range
• D well capacity / dark current

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• Dark Current
• It is produced by thermally generated carriers
  in depletion region.
• Total Noise

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• Signal To Noise Ratio (SNR)
• For visible region

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Applications

• CCD imaging systems in astronomy.
• The acquisition, guiding and wave front sensing
  applications in astronomy.
• Fabry-Perot CCD annular-summing spectroscopy.
• Electron-bombarded CCD detectors for ultraviolet
  atmospheric remote sensing.
• MAXDOAS instrument at Bremen.
• To retrieve the 2-dimensional distribution of the
  intensity.

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Advantages of CCD

• Quantum efficiency (QE) 80
• Low noise.
• High dynamic range.
• High photometric precision.
• Very linear behavior.
• Immediate digital conversion of data.

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• Low voltages required (5V-15V)
• Geomatrically stable (Good for astronomy).
• Rapid clocking.
• Disadvantages of CCD
• Limited exposure time.
• Cooling required to reduce noise.

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• Blooming or bleeding in columns due to bright
  sources.

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References

• Spectral Imaging of the Atmosphere (Gordon
  G.shepherd),June1999
• http//www.astro.virginia.edu/class/oconnell/astr5
  11/lec11-f03.html
• http//chemistry.hull.ac.uk/lectures/adw/06
• spiff.rit.edu/.../ lectures/ccd1/ccd1.html
• Semiconductor Radiation Detectors by Gerhard
  Lutz,1999.
• Single Particle Detection and Measurement by
  R.Gilmore,1992.
• http//www.iup.uni-bremen.de/doas/doas_glossary.ht
  m

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Thanks for your attention.