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

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  • 06/02/2008CCDs1 Charge Coupled Device M.Umar Javed M.Umar Javed
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  • 06/02/2008CCDs2 Outlines Basics Photodiodes Photodiode Arrays Charge Coupled Device (CCD) History and Principle of working Characteristics Applications Advantages and Disadvantages References
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  • 06/02/2008CCDs3 Photodiode A photodiode is a PN junction or PIN structure.
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  • 06/02/2008CCDs4 Operation Modes Forward Bias
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  • 06/02/2008CCDs5 Reverse Bias
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  • 06/02/2008CCDs6 Characteristics of PN Junction
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  • 06/02/2008CCDs7 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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  • 06/02/2008CCDs8 The photodiode array is a multichannel detector. They are useful in recording UV-Vis absorption spectra of samples.
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  • 06/02/2008CCDs9 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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  • 06/02/2008CCDs10 History The Charge Coupled Device was conceived in 1970 at Bell Labs by W.Boyle and G.Smith. Working Principle 1Generate Charge Photoelectric Effect 2Collect 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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  • 06/02/2008CCDs13 The voltages supplied to the electrodes change, and the electron packets move in response.
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  • 06/02/2008CCDs15 CCD Characteristics Quantum Efficiency (%)= It is the ratio between photogenerated carriers to incident photons per pixel.
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  • 06/02/2008CCDs16 Typical peak values Photographic plate= 1-2% Eye =1-2% Photomultiplier tube=20-30% CCD= 70-90% (HgCdTe)=30-50%
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  • 06/02/2008CCDs17 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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  • 06/02/2008CCDs18 Dynamic Range D = well capacity / dark current
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  • 06/02/2008CCDs19 Dark Current It is produced by thermally generated carriers in depletion region. Total Noise
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  • 06/02/2008CCDs20 Signal To Noise Ratio (SNR) For visible region
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  • 06/02/2008CCDs21 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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  • 06/02/2008CCDs22 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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  • 06/02/2008CCDs23 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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  • 06/02/2008CCDs24 Blooming or bleeding in columns due to bright sources.
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  • 06/02/2008CCDs25References Spectral Imaging of the Atmosphere (Gordon G.shepherd),June1999 http://www.astro.virginia.edu/class/oconnell/astr511/lec1 1-f03.html http://www.astro.virginia.edu/class/oconnell/astr511/lec1 1-f03.html http://www.astro.virginia.edu/class/oconnell/astr511/lec1 1-f03.html http://chemistry.hull.ac.uk/lectures/adw/06 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.htm
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  • 06/02/2008CCDs26 Thanks for your attention.