06/02/2008ccds1 charge coupled device m.umar javed m.umar javed

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06/02/2008 06/02/2008 CCDs CCDs 1 Charge Coupled Charge Coupled Device Device M.Umar Javed M.Umar Javed

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Page 1: 06/02/2008CCDs1 Charge Coupled Device M.Umar Javed M.Umar Javed

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Charge Coupled Charge Coupled DeviceDevice

M.Umar M.Umar JavedJaved

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OutlinesOutlines

BasicsBasics PhotodiodesPhotodiodes Photodiode ArraysPhotodiode Arrays

Charge Coupled Device (CCD)Charge Coupled Device (CCD) History and Principle of workingHistory and Principle of working CharacteristicsCharacteristics Applications Applications Advantages and DisadvantagesAdvantages and Disadvantages

ReferencesReferences

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PhotodiodePhotodiode A photodiode is a PN

junction or

PIN structure.

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Operation ModesOperation Modes

Forward Bias

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Reverse Bias

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Characteristics of PN JunctionCharacteristics of PN Junction

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Photodiode ArraysPhotodiode 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)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

11 Generate Charge Generate Charge Photoelectric Effect Photoelectric Effect

22 Collect Charge Collect Charge Pixels (gates) Pixels (gates)

3 Transfer Charge 3 Transfer Charge Apply a differential voltage Apply a differential voltage across gates. Signal electrons move down, across gates. Signal electrons move down, vertical registers to horizontal register. vertical registers to horizontal register.

4 Detect Charge 4 Detect Charge Individual charge packets are Individual charge packets are converted to an output voltage. 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 CharacteristicsCCD Characteristics Quantum Efficiency (%)=Quantum Efficiency (%)=It is the ratio between It is the ratio between

photogenerated carriers to incident photons per pixel.photogenerated carriers to incident photons per pixel.

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Typical peak valuesTypical peak values

Photographic Photographic plate= 1-2%plate= 1-2%

Eye =1-2%Eye =1-2% Photomultiplier Photomultiplier

tube=20-30%tube=20-30% CCD= 70-90%CCD= 70-90% (HgCdTe)=30-50%(HgCdTe)=30-50%

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Charge Transfer Efficiency (CTE)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 VariationPixel to Pixel Variation

This is fixed pattern noise because of the cell to cell non-uniformity..

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Dynamic RangeDynamic Range

D = well capacity / dark currentD = well capacity / dark current

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Dark CurrentIt is produced by thermally generated carriers in depletion region.

Total NoiseTotal Noise.BkTI Ae

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Signal To Noise Ratio (SNR)Signal To Noise Ratio (SNR)

For visible region For visible region

2 2 2

. .

. ( ) .B D R

S B tSNR

B t S S B N N

0BS

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ApplicationsApplications 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 CCDAdvantages 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 CCDDisadvantages of CCD Limited exposure time. Limited exposure time. Cooling required to reduce noise.Cooling required to reduce noise.

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Blooming or bleeding in columns due to Blooming or bleeding in columns due to bright sources.bright sources.

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ReferencesReferences

Spectral Imaging of the Atmosphere (Gordon Spectral Imaging of the Atmosphere (Gordon G.shepherd),June1999G.shepherd),June1999

http://www.astro.virginia.edu/class/oconnell/astr511/lec1http://www.astro.virginia.edu/class/oconnell/astr511/lec11-f03.html1-f03.html

http://chemistry.hull.ac.uk/lectures/adw/06http://chemistry.hull.ac.uk/lectures/adw/06 spiff.rit.edu/.../ lectures/ccd1/ccd1.htmlspiff.rit.edu/.../ lectures/ccd1/ccd1.html Semiconductor Radiation Detectors by Gerhard Semiconductor Radiation Detectors by Gerhard

Lutz,1999.Lutz,1999. Single Particle Detection and Measurement by Single Particle Detection and Measurement by

R.Gilmore,1992.R.Gilmore,1992. http://www.iup.uni-bremen.de/doas/doas_glossary.htmhttp://www.iup.uni-bremen.de/doas/doas_glossary.htm

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Thanks for your attention.Thanks for your attention.