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CCD vs EMCCD vs ICCD | difference between CCD, EMCCD, ICCD

This page compares CCD vs EMCCD vs ICCD and mentions difference between CCD, EMCCD and ICCD. CCD stands for Charge Coupled Device, EMCCD stands for Electron Multiplying CCD and ICCD stands for Intensified CCD.

Introduction:
Scientific Digital cameras come in four primary types based on sensor technology employed. These technologies are CCD, EMCCD, CMOS and ICCD.

CCD | Charge Coupled Device

CCD structure

CCD transfers each pixel's charge packet sequentially to convert its charge to a voltage. CCDs consist of array of thousands to millions of light sensitive elements known as pixels etched on silicon surface. Each of the pixels is buried channel MOS capacitor. CCDs are fabricated using p-type substrate and buried channel is implemented by forming thin n-type region on this surface. The size of CCDs are specified in Megapixels. A megapixel value is equivalent to multiplication of number of pixels in a row and number of pixels in a column.

Let us understand operation of CCD sensor.
• When sensor array is exposed to light, number of electrons (i.e. quantum of charge) held under certain pixel will vary directly as per luminous intensity exposure of that particular pixel.
• Charge is read out by suitable electronics and converted into digital bit pattern which can be analyzed and stored on the computer. This digital bit pattern represents the image.
• In order to record images in full colour, Bayer's color filter array is bonded to sensor substrate. This filter array is made of alternating rows of red/green, blue/green filters and known as RGBG filter. A particular color filter allows photons of that color to pass through to the pixel.
Refer CCD versus CMOS >> for difference between CCD and CMOS sensors.

EMCCD | Electron Multiplying CCD

EMCCD structure

EMCCD uses electron multiplying structure on chip. Hence EMCCD can detect single photon events without image intensifier. The EMCCD has essentially the same structure as CCD with the addition of a very important feature.

The stored charge is transferred through the parallel registers to a linear register as before but now prior to being readout at the output node the charge is shifted through an additional register, the multiplication register in which the charge is amplified. A signal can therefore be amplified above the readout noise of the amplifier and hence an EMCCD can have a higher sensitivity and higher speed than a CCD. This is due to amplification of charge signal before charge amplifier. The figure-2 depicts EMCCD structure.

ICCD | Intensified CCD

ICCD structure

To overcome limitations of CCD (Charge Coupled Device), ICCD has been developed. It exploits optical amplification provided by image intensifier to overcome the limitations of basic CCD sensor.

ICCD comprises of image intensifier tube coupled with traditional CCD sensor device. Light output of tube is coupled with CCD in two ways viz. using fiber optic coupler and lens coupled. These are the two possible type of constructions in ICCD. Lens coupled type used lens between output of image intensifier and CCD instead of fiber coupler. The figure-3 depicts fiber coupled ICCD type. The major component in ICCD design is power supply which generates DC voltages and voltage pulses for its operation. Refer advantages and disadvantages of ICCD >> over traditional CCD sensor.

Tabular difference between CCD, EMCCD and ICCD

Following table compares CCD vs EMCCD vs ICCD and summarizes difference between CCD, EMCCD and ICCD.

Features Ideal CCD EMCCD ICCD
Full Form - Charge Coupled Device Electron Multiplying CCD Intensified CCD
Quantum Efficiency (%) 100 93 93 50
Readout Noise 0 10 60 20
Gain 1 1 1000 1000
Spurious Noise 0 0.05 0.05 0
Dark Noise 0 0.001 0.001 0.001
Noise factor 1 1 1.41 1.6


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