<P> Besides the extremely high sensitivity of ICCD cameras, which enable single photon detection, the gateability is one of the major advantages of the ICCD over the EMCCD cameras . The highest performing ICCD cameras enable shutter times as short as 200 picoseconds . </P> <P> ICCD cameras are in general somewhat higher in price than EMCCD cameras because they need the expensive image intensifier . On the other hand, EMCCD cameras need a cooling system to cool the EMCCD chip down to temperatures around 170 K . This cooling system adds additional costs to the EMCCD camera and often yields heavy condensation problems in the application . </P> <P> ICCDs are used in night vision devices and in various scientific applications . </P> <P> An electron - multiplying CCD (EMCCD, also known as an L3Vision CCD, a product commercialized by e2v Ltd., GB, L3CCD or Impactron CCD, a now - discontinued product offered in the past by Texas Instruments) is a charge - coupled device in which a gain register is placed between the shift register and the output amplifier . The gain register is split up into a large number of stages . In each stage, the electrons are multiplied by impact ionization in a similar way to an avalanche diode . The gain probability at every stage of the register is small (P <2%), but as the number of elements is large (N> 500), the overall gain can be very high (g = (1 + P) N (\ displaystyle g = (1 + P) ^ (N))), with single input electrons giving many thousands of output electrons . Reading a signal from a CCD gives a noise background, typically a few electrons . In an EMCCD, this noise is superimposed on many thousands of electrons rather than a single electron; the devices' primary advantage is thus their negligible readout noise . It is to be noted that the use of avalanche breakdown for amplification of photo charges had already been described in the U.S. Patent 3,761,744 in 1973 by George E. Smith / Bell Telephone Laboratories . </P>

Which part of the eye is equivalent to the charge-coupled device (ccd) in a digital camera