ULg - EMC Lab Cost 286 Wroclaw

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Research activities in Liège Ir. V. Beauvois,
Ir. S. Coets, Ir. M. Renard and Ir. Ph.
Camus V.Beauvois_at_ulg.ac.be
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1st Research interest conducted and radiated
emissions measurements on large systems Ir. V.
Beauvois, Ir. S. Coets and Ir. M.
Renard (Sorrento 2002 and Zurich 2003) in coll.
With Johan Catrysse (KHBO, Oostende,
Belgium) V.Beauvois_at_ulg.ac.be
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Conducted Emission Introduction
In the low frequency range 150kHz - 30MHz
, conducted emission measurements are performed
with
? a LISN (Line Impedance Stabilized Network) which

• prevents the EUT from the noise coming from the
  mains

? provides a defined impedance at the point of
measurement
? a passive voltage probe if LISN unavailable
(i.e. if currents too large)
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Conducted Emission - Measurement Setup
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Conducted Emission - Problems encountered

• Oppositely, the voltage probe (point 2) can be
  placed anywhere
• between points 1b and 3, depending on the
  accessibility of
• the EUT

Which signal voltage is measured (distributed
impedance between 1b and 3 not negligible) ??
?
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Conducted Emission - Six-pole Concept
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Cond. Emission - More accurate model
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Cond. Emission - Actual and Future Works
As the tests performed without LISN may not be
compared with those performed with LISN, the next
steps of the study are

• create a virtual power mains network similar
  to the
• LISN s one and perform measurements with the
  help of this
• LISN-equivalent network

? for instance by the use of an EMI filter
instead of the LISN
? an alternating method to the LISN could then be
reached
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Cond. Emission - Actual and Future Works (contd)

• time domain and frequency domain measurements
• are done.
• alternate measurement methods
• classical passive voltage probe (one or two
• with differential method)
• alternate probes and clamps (capacitive clamp,
• EM clamp, current probe)

• ? improve the sensitivity of the measurements and
  the signal
• processing to get more accurate results

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Radiated emission - Introduction
Theoretical test configuration
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Radiated emission - Problems encountered
? Noise coming from the environment.

• Multiple reflexions  against  the environment
  which leads
• to an over-estimation or an under-estimation
  of the emission
• of the EUT.

• The measurement cannot necessarily be performed
  at a
• 10 meters distance from the EUT.

• How many measurements are to be done? And where?

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Radiated emission - Solutions to consider

• Retrieve the right signal from noise by using
• a differential method.

• As the measurements cannot be performed at a 10
  meters
• (or 3 meters) distance, perform near-field
  measurements
• in addition with a near-field ? far-field
  transformation.

• Take into account the reflecting characteristics
  of the global
• environment

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2nd Research interest Characterization and
modelling of embedded systems emissions Ir. V.
Beauvois, Ir. Ph. Camus V.Beauvois_at_ulg.ac.be
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Architecture of embedded systems
Main clock
Data Transmission Lines
Level shifters
I/O Controller
µcontroller
Sensors and Actuators
Analog and Power Section
Memory
Power Supply
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• Fast switching occurs on the bus and
• transmission lines which leads to current
  pulses.
•  
• Current pulses produce electromagnetic
• emissions radiated through the P.C.B.
  traces,
• integrated circuits pads and connected
  cables.
•  
• For a given architecture and software,
• the current waveforms on the board
  connections
• can be evaluated - they are related to
  electromagnetic
• emission.
• By mean of Fourier transform the spectrum
• can be computed and compared with EMC limits.

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Typical waveforms Data bus
Data bus, address bus and control signal are
combined (summation) in time domain.   As signals
are synchronous (one main clock) phase is the
same for each signal at a given frequency -gt
spectrum can be easily computed.
One simple loop on 80C320 Dallas
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Typical waveforms Power supply

• White filtered noise
• for analog parts
• Simple pulse noise
• for switched circuits

7805 linear regulator (white noise with cut off
frequency near 1 MHz) and MAX232 level shifter
(245 kHz and harmonics)
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Typical waveforms Analog and Power section

• Classification into families of circuits
• with same noise signatures
•  White filtered noise and switching noise.

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First results and actual works

• Conducted and radiated emission of a 80C320 board
• were measured for different codes and compared
• with computed spectrum
•  
• computed spectrum components occur
• at the same frequency as in the measurement on a
  real circuit
• variation of amplitude follows a similar
  envelope.

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Actual and Future Works

• Characterization of a great number of boards
  same CPU with different clocks and different
  peripherals,
•  
• Better modelling of switching process and
  relationship with conducted and radiated noise.
•  
• VHDL modelling of CPU to gain a better
  comprehension of processor noise sources,
  synthesis into an FPGA and measurements in
  anechoic chamber.
•  
• Development of software tools to predict noise
  behaviour of embedded systems.