Newport 8000 - Laser Module Theory of Operation; Laser Interface; Limit DAC; Figure 20 - Laser Module Block Diagram

40 Chapter 3 Laser Diode Driver Module Operation
3.6 Laser Module Theory of Operation
Figure 20 shows the functionality of the Laser Module. The following sections detail
the theory of operation for each of the blocks in Figure 20.
The circuit block diagrams for each laser mode of operation are shown in Figure 21,
Figure 22, and Figure 23. The theory of operation for each mode of operation is
discussed in Sections 3.6.9 - 3.6.11.
Optically
Isolated
Serial
Bus
Microprocessor
To
Limit DAC
Fault Monitors
A/D Converter
Output On/Off
and
Slow Turn-On
Unregulated DC
Voltage
Regulator
Pass
Transistor
Output
Shorting
Output
Laser
Current
Sensing
Diode
Current
Feedback
Set Point
DAC
Modulation
Input Port
Photodiode
+
-
Voltage
Sensing
Figure 20 - Laser Module Block Diagram
3.6.1 Laser Interface
The laser interface provides optically isolated serial communications between the
laser board and the microprocessor. Control signals are passed to the laser board to
set the laser board status, current limit, current set points, and photodiode feedback
functions. Instructions and data are sent over the serial interface to the optical
barrier. Status and data are serially passed back to the microprocessor.
3.6.2 Limit DAC
The microprocessor loads the current limit value into the 12-bit DAC. The Limit
DAC converts a digital limit signal from the microprocessor to a voltage which
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