Digitization (Rate) - Princeton PIXIS-XB System User Manual

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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.

Digitization (Rate)

Introduction
After gain has been applied to the signal, the Analog-to-Digital Converter (ADC)
converts that analog information (continuous amplitudes) into a digital data (quantified,
discrete steps) that can be read, displayed, and stored by the application software. The
number of bits per pixel is based on both the hardware and the settings programmed into
the camera through the software (see "Readout," page 39).
Factors associated with digitization include the digitization rate and baseline offset. The
speed at which digitization occurs is software-selectable but baseline offset is factory-set.
These factors are discussed in the following paragraphs.
Digitization Rate {Speed}
PIXIS-XB cameras incorporate dual digitization (100 kHz/2 MHz), which means that you
have a choice of how quickly the data will be digitized. Dual digitization provides
optimum signal-to-noise ratios at both readout speeds. 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 2 MHz conversion speed is used for the fastest possible data
collection and the 100 kHz conversion speed is used where noise performance is the
paramount concern. Switching between the conversion speeds is completely under
software control for total experiment automation.
Note: In WinX, the ADC rate can be changed on the Experiment Setup|ADC tab. In
LightField, the speed is changed on the Analog-Digital Conversion expander.
PIXIS-XB System Manual Version 2