Product category:
Design and Development Software
News Release from: Flomerics | Subject: Flo/EMC
Edited by the Electronicstalk Editorial
Team on 24 May 2005
Simulation shows simple route to
compliance
Computer simulation helped to solve a difficult electromagnetic compatibility (EMC) problem caused by differential signalling used in high-speed buses.
Computer simulation helped to solve a difficult electromagnetic compatibility (EMC) problem caused by differential signalling used in high-speed buses The product consisted of a four-foot rack carrying multiple blades and enclosed in an aluminium chassis with honeycomb gasketting
This article was originally published on Electronicstalk on 20 Jun 2007 at 8.00am (UK)
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Recognising the potential for a problem in a printed circuit board that used no less than six high-speed buses, the designers had seemingly taken all possible precautions by sandwiching each of the bus traces in between ground planes.
Each of the buses operated at about 400MHz and had 800ps rise times.
When the product still failed to pass FCC Class A electromagnetic interference (EMI) testing, even with cables disconnected, the telecommunications equipment vendor that designed it called in Ron Matthews, President of Noise Doctors, a consulting firm based in Marlborough, Massachusetts, that specialises in EMC compliance.
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Matthews said he began the assignment by collecting as much design information as possible.
He obtained the Cadence files used to define the electrical design, the Pro/Engineer solid model used for the mechanical design, and the Ibis behavioural model of the digital drivers, which specifies voltage as a function of current and time.
The equipment vendor had also used a software package called Omega Plus from Quantic EMC to perform signal integrity analysis.
Based on the Ibis data, Omega Plus generated voltages and current on the board and, based on these values, predicted E (electric) and H (magnetic) fields in the vicinity of the board.
Then Matthews used a software package called Flo/EMC from Flomerics, also based in Marlborough, Massachusetts, to predict the EMI generated by the board and diagnose its causes.
Flo/EMC differs from general-purpose electromagnetic simulation software in that it uses the transmission line matrix (TLM) method for solving Maxwell's equations, which provides major advantages when performing EMC simulations.
The TLM method solves for all frequencies of interest in a single calculation and therefore captures the full broadband response of the system in one simulation cycle.
This is particularly advantageous for EMC analysis as potential resonances and emissions vary over a wide frequency spectrum.
Matthews simulated FCC Class A testing and the EMI numbers generated by the simulation closely matched the test results.
Matthews examined not just the amount of radiation but the path by which radiation escapes from the enclosure, and quickly discovered the problem.
The differential signal lines were routed between layers by plated through-hole vias.
These vias not only provided an escape from the shielding layers but also upset the differential balance, causing the common mode current to rise.
Redesigning the board probably would not have helped much, so Mathews searched for another solution.
The simulation also showed that a majority of the EMI escaped the cabinet though a couple of fan louvres near the top of the back of the chassis.
Matthews ran several additional simulations that showed that the product could pass Class A testing simply by increasing the shielding at this point.
Testing showed that this change did indeed solve the problem. Request a free brochure from Flomerics ...
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