2. EMC Basics concepts

Summary Basic Principles Specific Units Radiating element Emission Spectrum Susceptibility Spectrum Notion of margin Impedance Conclusion February 19

The EM wave propagates through the air Basic principles CONDUCTED AND RADIATED EMI Conducted mode Radiated mode The VDD supply propagates parasits The EM wave propagates through the air Two main coupling mechanisms may be distinguished: the conducted mode and the radiated mode. In conducted mode, the the parasitic perturbations are propagated from the main sources to the victims by interconnects. The supply lines are the main contributors to such coupling, as they are shared by several integrated circuits. Conducted coupling is the most common problem. In the case of radiated mode, the source is able to generate a strong radiated energy, that couple through the air to a victim integrated circuit. Several cases radiated coupling may be found in electronic systems with embedded radio-frequency sources (Mobile phones for example). Power Integrity (PI) Electromagnetic Interference (EMI) February 19

Specific Units THE “EMC” WAY OF THINKING Electrical domain Electromagnetic domain Voltage V (Volt) Current I (Amp) Impedance Z (Ohm) Z=V/I P=I2 x R (watts) Electric Field E (V/m) Magnetic field H (A/m) Characteristic impedance Z0 (Ohm) Z=E/H P=H2 x 377 (watts/m2) far field conditions February 19

Specific units AMPLITUDE IN DB VS. FREQUENCY IN LOG Frequency measurement Fourier transform Freq (Log) dB Spectrum analyser Distinguish contributions of small harmonics Cover very large bandwidth Volt Time Time domain measurement A very important mathematics tool is used in EMC, called the Fourier transform. It converts time domain voltage waveform into frequency domain energy contents. Usually we plot frequency domain waveforms in log for frequency and log for volts. Oscilloscope February 19

Specific units EMISSION AND SUSCEPTIBILITY LEVEL UNITS Voltage Units 0.001 0.1 0.01 1 0.0001 Milli Volt dBµV 0.00001 Voltage Units 0.1 10 1 100 0.01 Volt dBV 0.001 Wide dynamic range of signals in EMC → use of dB (decibel) For example dBV, dBA : Extensive use of dBµV Due to the wide dynamic range of signals in EMC, we use decibel instead of linear units. In other words, we replace µV, mV, kV and mega–volt by corresponding values. Both currents and voltage are described in dB. Radio frequency integrated circuits such as the ones used in mobile phones are sensitive to very small amplitudes of signal. Consequently, the dBµV unit is also commonly used. 0dBµV is equal to 1µV. February 19

Tools > dB/Unit converter Specific units EMISSION AND SUSCEPTIBILITY LEVEL UNITS 1 W 1 MW 1 KW Power (Watt) 1 mW (dBm) 1 µW 1 nW Power Units The most common power unit is the “dBm” (dB milli-Watt) 1 mV = ___ dBµV 1 W = ___ dBm Exercise: Specific units For power, we use the dBm unit, where m (very simply) means milli-watts. Fill the dBm/Watt scale according to this formulation. IC-EMC: 0dbm in 50  Tools > dB/Unit converter February 19

Radiating elements h RADIATED EMISSION Elementary “Hertz” current dipole. Short wire with a length << λ , crossed by a sinusoidal current with a constant amplitude Io h The radiation is linked to a loss of energy when an EM wave is propagated along a waveguide. Determining E and H field requires the resolution of Maxwell equations. This is not the aim of this presentation. Here, we present a basic model: the elementary or Hertz dipole, in order to show some important properties of the radiated emission. This basic approximation is useful to deal with some common simple problem with wires.

Radiating elements NEAR FIELD/FAR FIELD Close to the antenna Far from the antenna Near-field region Far-field region Non radiating field (non TEM wave) E and H decreases rapidly in 1/r³ Radiating field (TEM wave) E and H decreases in 1/r 100 MHz : Rlimit =____ February 19

Specification example for an IC emission Emission spectrum EMISSION LEVEL VS. CUSTOMER SPECIFICATION EMC compatible Parasitic emission (dBµV) Specification example for an IC emission 80 70 IC-EMC: load Emission > d60 > d60_vde.tab 60 50 Measured emission 40 30 IC-EMC: load Getting started > mpc > mpc_vde.tab 20 This slide shows a parasitic emission of an equipment vs. frequency. The green line is the measured emission, the violet line the upper limit specified to comply with electromagnetic emission. 10 -10 1 10 100 1000 Frequency (MHz) February 19

Customer's specified limit Emission spectrum LOW PARASITIC EMISSION IS A KEY COMMERCIAL ARGUMENT Emission FM RF GSM 100 dBµV Not EMC compliant Supplier A 80 Customer's specified limit 60 Supplier B 40 EMC compliant 20 Low parasitic emission is a key commercial argument. The characterization of the electromagnetic emission is usually presented in frequency domain, log/log, with the frequency in X axis, and the emission level in dBµV in Y axis. 0dBµV is 1µV, 40dBµV is 100µV, 80dBµV is equal to 10mV. For automotive applications, three frequency bands are worth of interest: the FM band near 100MHz, the short distance radio links near 400MHz and the mobile phone 900,1800 and 1900MHz. The IC in red (Supplier A) exhibits a very high level of harmonics in the three “sensitive” bands. Electronic systems using this component could not comply EMC regulations. The same IC from an other supplier B, pin-to-pin compatible, features a significantly lower level of emission, which will probably be compliant with the customer’s specifications. 10 100 1000 Frequency(MHz) February 19

Susceptibility spectrum IMMUNITY LEVEL HAS TO BE HIGHER THAN CUSTOMER SPECIFICATION Immunity level (dBmA) Specification for board immunity 50 Current injection limit 40 30 Measured immunity 20 10 -10 A very low energy produces a fault -20 This slide shows the susceptibility threshold an equipment vs. frequency. The green line is the measured susceptibility, the pink line the limit specified to comply with electromagnetic susceptibility, the 2nd green line at 40 dB represents the maximum injected level. This limit corresponds to a limit for equipment or a limit of destruction of the DUT. -30 -40 1 10 100 1000 Frequency (MHz) February 19

Parasitic emission (dBµV) Notion of margin WHY A MARGIN ? Parasitic emission (dBµV) Nominal Level Design Objective To ensure low parasitic emission ICs supplier has to adopt margins Margin depends on the application domain Domain Lifetime Margin Aeronautics Automotive Consumer Aero : 30 ans, 40 dB. Auto : 10 ans, 20 dB. Consumer : 1 an, 0 dB ! Margin : process = 3 dB, measurement = 3 dB, ageing = xx dB, environment = 6 dB Safety margin, Process dispersion, Measurement error/dispersion , Component/PCB/System Ageing, Environment February 19

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) February 19

Immunity vs. ageing (LTOL) 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) February 19

Impedance R,L,C VS. FREQUENCY Impedance profile of: 1 Ω resistor z11-1Ohm_0603.z 0603 = 1.6 x 0.8 mm Schematic diagram: February 19

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

Impedance R,L,C VS. FREQUENCY Impedance profile of: Inductance 47 µH (Zin_L47u.s50) Schematic diagram: February 19

Impedance R,L,C VS. FREQUENCY Impedance profile of: Ferrite Zin_FerriteBLM18HK102SN1.s50 Schematic diagram: February 19

Characteristic impedance CONDUCTOR IMPEDANCE OR CHARACTERISTIC IMPEDANCE Z0: Coaxial line Microstrip line From the electromagnetic point of view: Link to conductor geometry and material properties lossless conductor From the electric point of view : Equivalent electrical schematic Any conductor can be represented by a combination of R, L, C, G parameters. In most conductors, L and C are the most important. The characteristic impedance Z0 is in first approximation the square root of L/C. We say that the conductor is adapted with its load if |Z0|= R. In that case, although existing physically and electrically, the conductor is almost transparent to the signal from the generator to the load. February 19

Characteristic impedance IMPEDANCE MATCHING Why impedance matching is fundamental ? IC-EMC Impedance> impedance_mismatch.sch Not adapted: Adapted: Voltage Voltage If |Z0| is equal to R, the aspect of the signal (close to R at the far end of conductor) is very similar to the near end of the conductor (close to Volt generator). Now, if |Z0| is different from R, ringing may be observed meaning that the signal is disturbed significantly. This effect is significant above 10 MHz in cables, 100 MHz in packaging and 1 GHz inside ICs. time time February 19

Characteristic impedance CHARACTERISTIC IMPEDANCE Z0: Small conductor Large conductor What is the optimum characteristic impedance for a coaxial cable ? Or ? Small conductor Large conductor Power handling Bending weight Low loss Small capacitance Small inductance Low Impedance 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 = ___  Why do we often talk about 50 ohm adaptation? Why not 1 or 1 k ?. The answer may be found in cable design. A small radius a for the signal conductor would mean an easy bending, light cable, with low loss. But the high L/C ratio means a high impedance, and the small radius high dielectric loss due to a thick conductor. A conductor with large radius would be heavy, low impedance, uneasy to bend, but with high dielectric loss due to this oxide. The minimization of dielectric loss leads to Z0=77 , the minimization of power loss leads to Z0=32 . The compromise Z0=50  is a worldwide accepted standard. February 19

Characteristic impedance 50 OHM ADAPTED SYSTEMS Spectrum analyzer Tem cell Waveform generator Amplifier All these systems have something to do with 50 ohm adaptation. The spectrum analyser has a 50 ohm input impedance. It corresponds in this case to a physical resistance connected between the input signal and the ground. The waveform generator is 50 ohm adapted, meaning that its output resistance is 50 ohm. The amplifier input and output also feature a 50 ohm resistance. The TEM cell and GTEM cell used in EMC characterization are also 50 ohm adapted, meaning that the internal conductor is sized and placed in such a way the square root of the L/C ratio is 50ohm. Tools > Interconnect parameters February 19

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 <End> February 19