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Chapter 5 Gate Mode Operation 83
5.10 Controller Gain {Analog 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 level of gain is done on the
Acquisition —> Experiment Setup… —> ADC tab {Analog to Digital Conversion
expander}. Available options are:
•1 {Low}
Users who measure high-level signals may wish to select 1{Low} for digitization of
larger signals: more electrons are required per ADU. Since binning combines the
signal from two or more pixels, the user may also want to select
1 {Low} if binning
is being applied. In both instances, the goal is to prevent CCD saturation and
maximize signal acquisition.
• 2 {High}
Users who consistently measure low-level signals may wish to select 2 {High},
which requires fewer electrons to generate an ADU and reduces some sources of
noise. If saturation occurs at this setting,
1 {Low} should be selected.
The following three factors should be considered in order to make an appropriate gain
selection:
• The intensity of the incoming signal;
• Binning;
• CCD saturation.
5.11 Digitization
During readout, an analog signal representing the charge of each pixel (or binned group of
pixels) is digitized. The number of bits per pixel is 16.
Some PI-MAX4 cameras are equipped with two complete analog channels, including
separate A/D converters. Because the readout noise of CCD arrays increases with the
readout rate, it is sometimes necessary to trade off readout speed for high dynamic range.
The two analog converters, both high speed, are optimized for slower read rates by digitally
processing the signal in the camera before transferring it to the host.