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64 PIXIS System Manual Version 2.C
Controller Gain
Controller gain (a function of the preamplifier) is software-selectable and is used to
change the relationship between the number of electrons acquired on the CCD and the
Analog-to-Digital Units (ADUs or counts) generated. Selecting the amount of gain is
done on the Acquisition|Experiment Setup…|ADC tab {Analog to Digital
Conversion expander}. The choices are 1 {Low}, 2 {Medium}, and 3 {High}. Users
who measure high-level signals may wish to select Low to allow digitization of larger
signals. Medium is suitable for experiments within the mid-level intensity range. Users
who consistently measure low-level signals may wish to select High, which requires
fewer electrons to generate an ADU and reduces some sources of noise.
The "Certificate of Performance" supplied with the camera lists the measured gain values
at all settings.
Example: The following descriptions assume the Low Noise Readout Port has been
selected and that the actual incoming light level is identical in all three instances. The
numbers used illustrate the effect of changing a controller gain setting and may not
reflect actual performance: gain at the 1, 2, and 3 settings depends on the CCD
installed.
Readout Port
{Quality}
Controller Gain {Analog Gain} Selection
1 {Low}
2 {Medium}
3 {High}
Low Noise
4 e
-
/count
2 e
-
/count
1 e
-
/count
High Capacity
16 e
-
/count
8 e
-
/count
4 e
-
/count
Table 2. Example of Controller Gain {Analog Gain} vs. Readout Port
1 {Low} requires four electrons to generate one ADU. Strong signals can be acquired
without flooding the CCD array. If the gain is set to Low and the images or spectra
appear weak, you may want to change the gain setting to Medium or High.
2 {Medium} requires two electrons to generate one ADU. If the gain is set to
Medium and the images or spectra do not appear to take up the full dynamic range of
the CCD array, you may want to change the gain setting to High. If the CCD array
appears to be flooded with light, you may want to change the setting to Low.
3 {High} requires one electron to generate one ADU and some noise sources are
reduced. Because fewer electrons are needed to generate an ADU, weaker signals can
be more readily detected. Lower noise further enhances the ability to acquire weak
signals. If the CCD array appears to be flooded with light, you may want to change
the setting to Medium or Low.