Photometrics Cascade 128, User Manual, Page: 28 / 54

Chapter 3. Operating Features 17
Cascade:650/1K
Features
In absolute terms, the Cascade:650 and the Cascade:1K cameras have a greater
than 200X multiplication factor. An approximate relationship between the DAC
setting and charge multiplication factor for the Cascade:650 and the Cascade:1K is
shown in the graph below.
Figure 12. DAC Setting vs. Charge Multiplication Gain for Cascade:650 and Cascade:1K
As the software you are using may depict the multiplication gain differently, you
should refer to the documentation that comes with it for accurate information. For
example, a straightforward implementation will show a scale between 0 and 4095
with 0 being the minimum and 4095 representing the maximum multiplication gain.
Because of the exponential nature of the gain, it may be possible to achieve even
higher gains by increasing the voltage by only a small fraction at the higher end.
The charge multiplication also introduces additional noise, quantified by noise
factor (F). Typically, F is measured between 1.0 and 1.4.
Note: As the on-chip multiplication introduces additional noise, it is recommended that
the multiplication be used only as required. For more information, refer to the "On-Chip
Multiplication Gain" technical note. This technical note can be accessed by going to the
Photometrics web site at
www.photomet.com , clicking on "Library", clicking on
"Technical Notes", and selecting the title from the list of notes.
Conversion Gain
Apart from multiplication gain, which actually multiplies the number of
electrons generated in each pixel, the Cascade:650 and the Cascade:1K also have
three (3) conversion gains. Conversion gain simply quantifies how the resulting
electrons are converted into ADU (Analog-to-Digital) units and displayed on the
display screen.
Typical conversion gains for the readout port are listed in Table 1. Your camera
is individually calibrated for these gains. So, please refer to the certificate of
performance that accompanied your camera.