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Chapter 3
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.
To
Microprocessor
Modulation
Input Port
+ -
Photodiode
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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Laser Diode Driver Module Operation
Limit DAC
A/D Converter
Optically
Isolated
Serial
Bus
Fault Monitors
Output On/Off
and
Slow Turn-On
Set Point
DAC
Figure 20 - Laser Module Block Diagram
Unregulated DC
Voltage
Regulator
Pass
Transistor
Output
Output
Shorting
Voltage
Sensing
Current
Sensing
Current
Feedback
Laser
Diode
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