Research activities in Liège Ir. V. Beauvois , Ir. S. Coets, Ir. M. Renard and Ir. Ph. Camus

ULg - EMC Lab Cost 286 Wroclaw 1

Research activities in Liège

Ir. V. Beauvois, Ir. S. Coets, Ir. M. Renardand Ir. Ph. Camus

[email protected]


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)

[email protected]


Conducted Emission – Introduction

In the low frequency range [150kHz - 30MHz] ,conducted emission measurements are performed with:

a LISN (Line Impedance Stabilized Network) which

a passive voltage probe if LISN unavailable (i.e.

if currents too large)

prevents the EUT from the noise coming from the mains

provides a defined impedance at the point of measurement


Conducted Emission - Measurement

Setup


Conducted Emission - Problems encountered

With the LISN, the measurement is always performed at point 1b

The point of measurement is ‘‘standardized’’ (fixed)

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 impedancebetween 1b and 3 not negligible) ??

Solution: introduction of a new concept: the six-pole


Conducted Emission - Six-pole Concept

In this research, only single-phased situations are considered

concept of the six-pole

If three-phased situations with neutral (3P + N + PE)

ten-pole

If three-phased situations without neutral (3P + PE)

eight-pole


Cond. Emission - More accurate model

H1 : six-pole between mains and point of measurement (1b or 2)

EUT emission signal voltage

H2 : six-pole between point of measurement and EUT


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


Cond. Emission - Actual and Future Works (contd)

• time domain and frequency domain measurements are done.• alternate measurement methods :

- classical passive voltage probe (one or twowith 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


Radiated emission - Introduction

Theoretical test configuration:


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?


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


2nd Research interest:Characterization and modelling of

embedded systems emissions

Ir. V. Beauvois, Ir. Ph. Camus

[email protected]


Architecture of embedded systems

µcontroller

Main clock

Memory

I/OController

Analog and Power Section

Sensors and Actuators

Level shifters

Power Supply

Data Transmission

Lines


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.


Typical waveforms – Data bus

0 50 100 150 200 250 300 350 4000

1

2

3

4

5

6

7

Boucle while(1); durée =100 µs

t (µs)

0 20 40 60 80 100 120 140 1600

1000

2000

3000

4000

5000

f (kHz)

Data bus,address busand control signalare combined(summation) in time domain. As signals are synchronous(one main clock) phase isthe same for each signalat a given frequency-> spectrum can be easilycomputed.One simple loop on

80C320 Dallas


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)


Typical waveforms – Analog and Power section

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


First results and actual works

Conducted and radiated emission of a 80C320 boardwere measured for different codes and comparedwith 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.


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.

Research activities in Liège Ir. V. Beauvois , Ir. S. Coets, Ir. M. Renard and Ir. Ph. Camus

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