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QCL500, QCL1000, QCL1500 Low Noise Quantum Cascade Laser Drivers
PAGE 13
QCL1500-00400-D
APPLICATION NOTES
OPTIMIZE NOISE
Noise is specifi c to each application. Here are a few suggestions for reducing system noise:
•
Buy the right controller for your QCL. The lower the maximum current capacity, the lower the
current noise. Contact the factory for a custom range.
•
Manage ground loops. Any current fl owing through inadvertant ground loops will show as current
noise. See “Ground Loop Avoidance” Application Note.
•
Keep the ANALOG IN signal clean. Any noise on that input will transfer directly to the output
current.
•
If possible, tie the QCL driver chassis to ground (without introducing ground loops). This reduces
60 (or 50) Hz peaks. Pin 15 on the 20 pin connector is ground. It can be wired to a screw on the
chassis, to the mounting slots, etc. Note that despite the peak at 60 Hz, 0 ot 100 kHz RMS noise
for the two graphs is equivalent.
Figure 12:
60 Hz noise with chassis fl oating and chassis grounded
•
Choose the right power supply. Wavelength has tested with a switching TDK / Lambda power
supply (PWRPAK-24V) as well as linear supplies. The better the switching supply, the better the
noise performance. Specifi cations to look at are minimum noise and maximum load rejection.
Figure 13:
Example linear and switching power supply noise current density graphs.
Linear
Switching
•
Filter the power supply. Use an off-the-shelf EMI fi lter such as TDK / Lambda’s MAW series.
•
Fan wiring. Do not power a fan from the dual supplies. Keep it on a completely different power
supply.
•
Minimize lead length to the power supply and load. Use twisted pair, shielded cables, or SMAs.
