Product category:
Design and Development Software
News Release from: Flomerics | Subject: Flo/EMC
Edited by the Electronicstalk Editorial
Team on 28 September 2004
Software illustrates merits of proper
grounding
Recent research has indicated that electromagnetic emissions from interface cards can be reduced by as much as 20dB through simple changes in grounding arrangements.
Recent research has indicated that electromagnetic emissions from interface cards can be reduced by as much as 20dB through simple changes in grounding arrangements Stuart Charles of E-Mead Consulting performed the simulation study on paddle-board cards connected to the backplane of an equipment enclosure through connector pins
This article was originally published on Electronicstalk on 20 Jun 2007 at 8.00am (UK)
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The study focused on modelling the effectiveness of the grounding pins using the concepts of partial inductance.
Charles progressed using the Flo/EMC simulation software from Flomerics to investigate the impact of grounding, bonding and inductance in real-world designs which could not be easily be analysed by "pure" mathematics.
In the basic arrangement that Charles studied he showed that simply changing from one to four grounding pins in a "coaxial" topography reduced emissions by more than 20dB.
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"The results of this research study are equally applicable to daughterboards as paddle-boards", said Charles.
"It's often necessary to pass a clock signal in the 10 to 50MHz range to one of these boards, with one pin typically carrying the clock signal and the connector ground pins carrying the return".
"The Ldi/dt voltage drop across the connector ground pins excites the paddle-board and associated cable".
"This assembly then acts like an aerial that can potentially radiate beyond FCC (Federal Communications Commission) Class A limits".
Charles began the current study by using the concepts of partial self and mutual inductance to demonstrate the correlation between radiated emissions and the radio frequency (RF) voltage drop across the ground pins.
He began with a typical daughterboard with a 20MHz clock routed from the motherboard.
He calculated the partial self and partial mutual inductance of combinations of parallel conductors with the distance between them of less than their length and between 10 and 100 times their radius.
He then used the partial inductance concept to compute the "net inductance" of the ground wires or pins.
(The "L" in Ldi/dt).
Charles then used Flo/EMC to model the effectiveness of the grounding pins using the concepts of partial inductance.
The advantage of Flo/EMC over the "first principles" approach is that it is capable of modelling geometries of nearly any complexity and that it determines the real world quantitative impact of grounding arrangements while shielding the user from the complex mathematical analysis involved.
Flo/EMC makes it possible to identify EMC design issues early in the design cycle, well before physical prototypes are built.
The simulation tool uses the transmission line matrix (TLM) method for solving Maxwell's equations, solving for all frequencies of interest in a single calculation and therefore capturing the full broadband response of the system in one simulation cycle.
Charles used Flo/EMC to simulate five different grounding configurations, a reference design with a single ground pin, model 2 and 3 which both have two ground pins, model 4 which is a three ground pin arrangement, and model 5 which has four ground pins.
The results matched the theoretical calculations very closely.
When Charles compared the different grounding configurations, the simulation showed major differences between them from an EMC standpoint.
Models 2, 3, 4 and 5 generated 7, 9, 13 and 20dB, respectively, less emission than the reference design.
This study demonstrates how EMC simulation can substantially reduce emissions in real-world applications by allowing engineers to investigate many more alternatives that would be practical with physical prototypes.
It is planned to build a hardware demonstrator in late 2004 to investigate more complex grounding arrangements, and to study the effect of paddle board emissions with and without cables attached.
Flo/EMC will be used to provide correlation with the laboratory measurements for the radiated emissions signature and to investigate the geometric dependencies of different grounding arrangements and PCB structure dimensions. Request a free brochure from Flomerics ...
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