36 Chapter 4 Principles of Operation
4.2.8 Photodiode Feedback Amplifier
A precision Transimpedance amplifier provides photodiode feedback. When
constant Power mode is selected, the photodiode feedback signal is used to
control the laser output. A precision instrumentation amplifier is used to
amplify the thermopile’s voltage.
4.2.9 Constant Current, High Bandwidth Mode
This mode of laser operation is shown in Figure 14. In this mode, current
feedback is used to control the laser output.
4.2.10 Constant Current, Low Bandwidth Mode
This mode of laser operation is shown in Figure 15. In this mode, current
feedback is used to control the laser output.
In this mode, capacitors are switched into the circuit. These capacitors act as
a filter and therefore prevent the laser output from changing too rapidly. This
gives added laser diode protection. This also limits the laser output
bandwidth to about 10 kHz.
Internal
Modulation
Regulated
Supply
Modulation
Input Port
Current Set Point
Laser Diode
Current
Sense
Output
Shorting
Pass
Figure 14 - Constant Current - High Bandwidth Mode
Artisan Technology Group - Quality Instrumentation ... Guaranteed | (888) 88-SOURCE | www.artisantg.com
To Next Page
Loading...
