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Summary

- Basic Principles
- Specific Units
- LC Resonance
- Radiating element
- Emission Spectrum
- Susceptibility Spectrum
- Notion of margin
- Impedance
- Conclusion

Basic principles

CONDUCTED AND RADIATED EMI

Conducted mode

Radiated mode

The VDD supply propagates parasits

The EM wave propagates through the air

Power Integrity (PI)

Electromagnetic Interference (EMI)

Specific Units

THE “EMC” WAY OF THINKING

Specificunits

Distinguish contributions of small harmonics

dB

Volt

Freq (Log)

Time

Cover very large bandwidth

Frequency measurement

Fourier transform

Spectrum analyser

AMPLITUDE IN DB VS. FREQUENCY IN LOG

Time domain measurement

Oscilloscope

Specific units

Milli

Volt

Volt

dBV

dBµV

100

1

10

0.1

For example dBV, dBA :

1

0.01

0.1

0.001

Extensive use of dBµV

0.01

0.0001

0.001

0.00001

EMISSION AND SUSCEPTIBILITY LEVEL UNITS

Voltage Units

Wide dynamic range of signals in EMC → use of dB (decibel)

Specific units

Power

(Watt)

Power

(dBm)

1 MW

1 KW

1 W

1 mW

Exercise: Specific units

1 µW

1 mV = ___ dBµV

1 W = ___ dBm

1 nW

EMISSION AND SUSCEPTIBILITY LEVEL UNITS

Power Units

The most common power unit is the “dBm” (dB milli-Watt)

IC-EMC: 0dbm in 50

Tools > dB/Unit converter

LC Resonance

THE CHIP IS A LC RESONATOR

f= ___

- DSPIC33F DIE ALONE

Impedance (Ω)

Tools > LC resonance

Eurodots > z11-dspic-vdd_10-vss_9.z

Impedance measurement between Vdd and Vss

Frequency (Hz)

Radiating Element

RADIATED EMISSION

- Elementary “Hertz” current dipole.
- Short wire with a length << λ , crossed by a sinusoidal current with a constant amplitude Io

h

Radiating Element

NEAR FIELD/FAR FIELD

- Close to the antenna

- Far from the antenna

Near-field region

Far-field region

- Radiating field (TEM wave)
- E and H decreases in 1/r

- Non radiating field (non TEM wave)
- E and H decreases rapidly in 1/r³

100 MHz : Rlimit =____

LC Resonance

THE BOARD IS A RESONATOR

- The VDD/VSS plate acts as a capacitor

Impedance (Ω)

Eurodots > z11-board-d21on.z

Frequency (Hz)

Emission spectrum

EMISSION LEVEL VS. CUSTOMER SPECIFICATION

EMC compatible

Specification example for an IC emission

Parasitic emission (dBµV)

80

70

60

50

Measured emission

40

30

20

10

0

-10

1

10

100

1000

Frequency (MHz)

Emission spectrum

Not EMC compliant

Customer's specified limit

EMC compliant

LOW PARASITIC EMISSION IS A KEY COMMERCIAL ARGUMENT

Emission

FM

GSM

RF

100

dBµV

Supplier

A

80

60

Supplier

B

40

20

0

10

100

1000

Frequency(MHz)

Susceptibility spectrum

IMMUNITY LEVEL HAS TO BE HIGHER THAN CUSTOMER SPECIFICATION

Immunity level (dBmA)

Specification for board immunity

Current injection limit

50

40

30

Measured immunity

20

10

0

-10

A very low energy produces a fault

-20

-30

-40

1

10

100

1000

Frequency (MHz)

Notion of margin

Parasitic emission (dBµV)

Nominal Level

Design Objective

WHY A MARGIN ?

- To ensure low parasitic emission ICs supplier has to adopt margins

- Margin depends on the application domain

Notion of margin

INFLUENT PARAMETERS ON IC EMC

- The variability between components induce a dispersion of emission and susceptibility level. Radiated emission in TEM cell of a 16 bit microcontroller PIC18F2480. Measurement of 12 samples and extraction of emission level dispersion.

- The temperature of a circuit has a direct impact on the switching time of internal devices. When temperature increases, the high frequency content of the emission spectrum tends to be reduced.

Std deviation = 1.7 dB

K. P. Slattery et al., “Modeling the radiated emissions from microprocessors and other VLSI devices”, IEEE Symp. on EMC, 2000.

H. Huang and A. Boyer (LAAS-CNRS)

Notion of margin

INFLUENT PARAMETERS ON IC EMC

- MOS device characteristics fluctuate by +/- 30 %

- Ageing may significantly alter EMC performances

Ioff/Ion MOS

32-nm

PhD A. C. Ndoye, INSA, 2010

Immunity vs. ageing (LTOL)

Characteristic Impedance

- From the electromagnetic point of view:

Coaxial line

Microstrip line

Link to conductor geometry and material properties

- From the electric point of view :

lossless

conductor

Equivalent electrical schematic

CONDUCTOR IMPEDANCE OR CHARACTERISTIC IMPEDANCE Z0:

Characteristic Impedance

IMPEDANCE MATCHING

Why impedance matching is fundamental ?

IC-EMC

Impedance>

impedance_mismatch.sch

Not adapted:

Adapted:

Voltage

Voltage

time

time

Characteristic Impedance

Small conductor

Large conductor

CHARACTERISTIC IMPEDANCE Z0:

What is the optimum characteristic impedance for a coaxial cable ?

Or ?

Ideal values:

- Maximum power : Z0 = ___

- Minimum loss: Z0 = ___

Cable examples:

- EMC cable (compromise between power and loss) : Z0 = ___
- TV cable : Z0 = ___
- Base station cable : Z0 = ___

Characteristic Impedance

50 OHM ADAPTED SYSTEMS

Spectrum analyzer

Tem cell

Waveform generator

Amplifier

Tools > Interconnect parameters

Conclusion

- Specific units used in EMC have been detailed
- The current dipole is the base for radiated emission
- The Emission Spectrum has been described
- Susceptibility Threshold, margins have been discussed
- The notion of impedance has been introduced
- Characteristic impedance of cables lead to specific values
- Discrete components used in the experimental board have been modeled up to 1 GHz

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