Photometrics Cascade 128, Руководство пользователя, Страница: 30 / 54

Chapter 3. Operating Features 19
Cascade:512F/
512B/128+/128
Features
A 12-bit DAC is provided to control the multiplication gain of the Cascade: 512F,
Cascade:512B, Cascade:128+, and Cascade:128 in 4096 steps. A DAC setting of
zero (0) refers to a no-gain state where the camera behaves like a standard high
speed CCD (with rather high read noise). Settings 1 to 4095 are mapped linearly to
the internal serial clock voltages that vary the multiplication gain in a complex
exponential fashion. Typically at a DAC setting of 4095, Cascade:
512F/512B/128+/128 can offer multiplication gain factor in the excess of 1000x.
Even though the camera is capable of delivering large multiplication gain factors,
multiplication gain should be used only as needed to preserve as much dynamic
range as possible.
An approximate relationship between the DAC setting and charge multiplication
factor for the Cascade:512F, 512B, 128+, and 128 is shown in the graph below.
Figure 13. DAC Setting vs. Charge Multiplication Gain for Cascade:512F/512B/128+/128
Dual-Readout Port
Operation
The Cascade:512F and 512B can be configured with software-selectable dual-
readout amplifiers, also referred to as "ports", shown in
Figure 14 . The two
amplifiers are listed below.
Port #1: On-chip Multiplication amplifier
Port #2: Traditional or non-multiplication amplifier
Normal Voltage Clock
Standard Serial Register
Frame-transfer Area
Sensor Area
High Voltage Clock
Readout
Amplifier
Output or Sensor Node
Extended Multiplication Register
Readout
Amplifier
Output or Sensor Node
Port #2 (non-multiplication)
For standard, high dynamic range
applications. Available in
Cascade:512F and Cascade:512B only.
Port #1 (multiplication)
For high speed, low light level
applications.
Cascade:512F/512B CCD
Figure 14. Cascade:512F and 512B CCD Array Structure