APPENDIX
iKon-L APPENDIX
Page 162
A1.1.14 - Saturation
Saturation is the largest signal the CCD can measure. A signal is measured in terms of the amount of charge
that has built up in the individual pixels on the CCD-chip. A number of factors determine the maximum amount
of charge that the CCD can handle.
A1.1.15 - Scan Types: Keep Clean & Acquired
The CCD is continually being ‘scanned’ to prevent its becoming saturated with dark current (see dark signal).
If the Scan is being used simply to ‘clean’ the CCD (i.e. it is a keep-clean scan), the charge from the CCD is
discarded.
In an acquired scan, however, the charge undergoes A/D conversion and is acquired into computer memory
so that it can be used for subsequent processing and display: it is ‘read out’ (see Readout previously). In this
User’s Guide ‘scan’ generally refers to an acquired scan - unless the context specifically indicates otherwise.
The Shift Register usually consists of a single row of elements (or pixels) running parallel to and below the
bottom row of light-gathering pixels (the image area) on the CCD-chip. The shift register is protected from light
by an aluminum mask. The elements in the shift register have a greater capacity to store charge (a greater
‘well depth’) than the other pixels on the CCD-chip.
Shot Noise is due to basic physical laws and cannot be removed. Any signal, whether it be a dark signal or a
light signal, will have shot noise associated with it. Most simply defined:
• If the signal or dark signal = N electrons, the shot noise is the square root of N.
You can do nothing about the shot noise of your signal, but by choosing minimum exposures and operating the
CCD at suitably low temperatures, the dark signal, and hence the noise from the dark signal, can be reduced.
A1.1.18 - Signal to Noise Ratio
The Signal to Noise Ratio (more commonly abbreviated as S/N or
The maximum Signal to Noise Ratio is the ratio between the maximum signal (i.e. the saturation level) and the
noise associated with that signal. At near saturation levels the dominant source of noise is the shot noise of the
signal.
SNR) is the ratio between a given signal
and the noise associated with that signal. Noise has a fixed component, and a variable component (shot
noise) which is the square root of the signal. Thus, the Signal to Noise Ratio usually increases (improves) as
the signal increases.
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