February Meeting Notice, Santa Clara Valley IEEE EMC Society
When
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February 9, 1999
Where
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Dinner 5:30 - 7:30 PM
Auspex Cafeteria, 2300 Central Expressway, Buliding A, Santa Clara
Technical Presentation 7:30 - 9:30 PM
Auspex, 2300 Central Expressway, Building A, Santa Clara, CA
Speaker/Topic
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Robert Dockey, HP, "New Techniques for Reducing PCB Common-Mode Radiation"
Details
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On February 9, 1999, the Santa Clara Valley Chapter of the IEEE EMC
Society will hear a presentation by Robert Dockey of HP on
"New Techniques for Reducing PCB Common-Mode Radiation."
Have you ever had the experience of believing that you had done everything
humanly possible to reduce the radiated emissions from an unshielded printed
circuit assembly and yet still measure unacceptable margins? If so, this
presentation could help explain the reasons why. Even when all of the
common emission suppression measures like power supply decoupling, cable
filtering, loop area control and full ground planes have been
utilized, there is still one dominant coupling mechanism remaining which can
be manipulated to improve the margin. Unfortunately it may also set a lower
limit on the possible emission level which can be obtained from a specific
design. This mechanism is referred to as ìGround Plane Voltage Gradient
contamination. This presentation will attempt to describe and analyze this
radiated emission mechanism and present several design techniques which can
be used to deal with it successfully.
A multi-layer printed circuit board with a "good ground plane" can produce
common-mode radiation similar to a dipole antenna. This ground plane is
commonly thought of as a low impedance path for returning currents and one
which is of constant potential across its area.
In 1993, Dockey discovered that a relatively small PCB with a solid
ground-plane could also produce common-mode radiation. On this truncated
Microstrip transmission-line, the majority of the signal-trace current returns
on the ground plane beneath the signal trace.
This presentation will elaborate on these findings and propose several methods
which can be used to effectively mitigate the radiation mechanisms.
Bob has been with Hewlett Packard for 13 years as both an EMC engineer and
engineering manager. Previously, he spent 13 years as a TEMPEST engineering
manager for TRW in Colorado Springs, Colo.
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