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EMC Basics concepts

EMC Basics concepts. 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.

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EMC Basics concepts

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  1. EMC Basics concepts

  2. Summary • Basic Principles • Specific Units • LC Resonance • Radiating element • Emission Spectrum • Susceptibility Spectrum • Notion of margin • Impedance • Conclusion

  3. 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)

  4. Specific Units THE “EMC” WAY OF THINKING

  5. 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

  6. 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)

  7. 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

  8. 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)

  9. 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

  10. 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 =____

  11. LC Resonance THE BOARD IS A RESONATOR • The VDD/VSS plate acts as a capacitor Impedance (Ω) Eurodots > z11-board-d21on.z Frequency (Hz)

  12. 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)

  13. 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)

  14. 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)

  15. 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

  16. 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)

  17. 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)

  18. Impedance R,L,C VS. FREQUENCY Impedance profile of: • 1Ω resistor (z11-1Ohm_0603.z) Schematic diagram:

  19. Impedance R,L,C VS. FREQUENCY Impedance profile of: • 1 nF capacitor (z11-C1nF_0603.z) Schematic diagram:

  20. Impedance R,L,C VS. FREQUENCY Impedance profile of: • Inductance 47 µH (Zin_L47u.s50) Schematic diagram:

  21. 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:

  22. Characteristic Impedance IMPEDANCE MATCHING Why impedance matching is fundamental ? IC-EMC Impedance> impedance_mismatch.sch Not adapted: Adapted: Voltage Voltage time time

  23. 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 = ___ 

  24. Characteristic Impedance 50 OHM ADAPTED SYSTEMS Spectrum analyzer Tem cell Waveform generator Amplifier Tools > Interconnect parameters

  25. 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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