Transcript Intensified CCD

The CCD sensor was invented in 1969 by
Willard Boyle and George E. Smith of
AT&T Bell Labs.
 Originally intended as a memory device
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Pixel: Picture Element
 CCD: Charge-Coupled Device
 CMOS: Complimentary Metal-Oxide
Semiconductor
 Panchromatic: Sensitivity to a wide
range of wavelengths of light.
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Photoelectric effect creates an
electron-hole pair when light impinges
upon a semiconductor
Each pixel accumulates a charge
When sampled, the “bucket of charge”
for each pixel is transported off-chip to
on off-chip amplifier
A capacitor is used to convert the
charge to a voltage. V = q/C
Used largely in military and scientific
applications.
 The image-intensifier is added to a CCD
to create an intensified CCD.
 Provides single-photon sensitivity
 Also enables extremely short exposure
times. (down to 200ps)
 It reduces the shortcomings of a bare
CCD
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A
B
Phosphor Screen
Photocathode
Micro-channel Plate (MCP)
A: 200V Gating Voltage (variable)
B: 1000V Micro-channel plate
C: 6kV acceleration voltage
C
A > 0: Shutter is open (gated)
A < 0: Shutter is closed
A
B
Phosphor Screen
Micro-channel Plate (MCP)
Photocathode
e-
e- s (1000x)
A: 200V Gating Voltage (variable)
B: 1000V Micro-channel plate
C: 6kV acceleration voltage
C
A > 0: Shutter is open (gated)
A < 0: Shutter is closed
Phosphor Screen
Micro-channel Plate (MCP)
Photocathode
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Is officially defined as the percentage of
photons hitting a surface that will
produce electron-hole pairs
› Regular photographic film is about 10%
› Human Eye is about 3%
› CCDs can have a QE of more than 90% at
some wavelengths
Useful for rating solar cells
 Doesn’t account for unwanted
recombination in material

Quantum Efficiency of CCD used in Hubble Space Telescope’s
Wide-Field and Planetary Camera 2
When charges are shifted from pixel to
pixel it is the loss associated with each
shift. A value of 0.999 is actually bad!
 Most CCDs use 2000-4000 shifts to read a
single pixel out.

Thermal excitations can excite electrons
into the conduction band
 This is the reason that most CCDs require
extensive cooling (-90 to -40 °C)

Electronic amplifiers are not perfect and
introduce their own noise.
 This determines the “noise floor” of the
CCD. It sets the limitation of how faint of
an object a CCD can see.
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Optically insensitive structures for each
pixel (absorption loss)
 Natural reflection of certain wavelengths
(reflection loss)
 Very long and very short wavelengths
pass straight through sensor without
generating an electron (transmission loss)
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CCDs are simple application of the
photoelectric effect
 Intensified CCDs improve the light
sensitivity of a bare CCD
 Intensified CCDs are used in military and
scientific application (mostly astronomy)
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http://www.asiimaging.com/pdfs/Comparison_of_CCD_Cameras_to_an_Ide
al_Camera.pdf
http://www.andor.com/learn/digital_cameras/?docid=326
http://www.dalsa.com/dc/documents/Image_Sensor_Architecture_Whitepa
per_Digital_Cinema_00218-00_03-70.pdf
http://www.dalsa.com/markets/ccd_vs_cmos.asp
http://www.iccd-camera.com/technology_main.html
http://en.wikipedia.org/wiki/Quantum_efficiency
http://wfc3.gsfc.nasa.gov/MARCONI/machines-see.html