Rohde & Schwarz EMI/EMC debugging with modern oscilloscope. Ing. Leonardo Nanetti Rohde&Schwarz

Transcription

1 Rohde & Schwarz EMI/EMC debugging with modern oscilloscope Ing. Leonardo Nanetti Rohde&Schwarz

2 EMI debugging Agenda l The basics l l l l The idea of EMI debugging How is it done? Application example What now? EMI/EMC debugging with a moder oscilloscope 2

3 EMI debugging Agenda l The basics l l l l The idea of EMI debugging How is it done? Application example What now? EMI/EMC debugging with a moder oscilloscope 3

4 EMI debugging The challenge l For example: IoT devices l This could be anything from a 5,- sensor to a ,- device l According to EEtimes.com article: approx. 90% fail initial compliance testing First pass compliance test Pass Fail Source: EEtimes.com, IoT Devices: Most initially Fail EMI testing EMI/EMC debugging with a moder oscilloscope 4

5 Application: EMI debugging What is EMI? EMC ElectroMagnetic Compatibility EMI ElectroMagnetic Interference EMI Emissions EMS ElectroMagnetic Susceptibility EMS Immunity RE Radiated Emissions CE Conducted Emissions RS Radiated Susceptibility CS Conducted Susceptibility EMI/EMC debugging with a moder oscilloscope 5

6 Introduction to EMI The Problems and Challenges Money and time Trend for Embedded System Design EMI/EMC debugging with a moder oscilloscope 9

7 Preventive measures Application: EMI debugging Time vs. Money PCB, Filtering, Ground bounce, software and etc. Pre-compliance Compliance Effectiveness & available measures Cost incurred R&D Prototype Pre-Production Manufacturing Phase Design Manufacturing EMI/EMC debugging with a moder oscilloscope 10

8 Application: EMI debugging EMC is not a new problem, but ı Trend for Embedded System Design l Faster clock speed l Smaller form factor l More data lines for communications l More design include RF technology l Power has more impact on signals with smaller amplitude Via s Tiny-ITX ı More EMI issues motherboard l Higher speed design introduces more EMI issues l Bad PCB Layout (stacking) causing worse EMI l RF features impact & be susceptible to EMI l Driven by the discontinuities and resonances of the transmission path Cell Phone EMI/EMC debugging with a moder oscilloscope 11

9 EMI debugging Agenda l The basics l l l l The idea of EMI debugging How is it done? Application example What now? EMI/EMC debugging with a moder oscilloscope 13

10 Application: EMI debugging Concept Design Prototype Verify Pre-production Design for test first level debugging Pre-compliance Compliance R&S ESL EMI Test Receiver Conducted and radiated measurement Precompliance and compliance acc. to CISPR/EN/MIL/etc. standard High measurement speed Disturbance measurement R&S ESW R&S ESRP R&S ESR EMI/EMC debugging with a moder oscilloscope 15

11 EMI debugging Agenda l The basics l l l l The idea of EMI debugging How is it done? Application example What now? EMI/EMC debugging with a moder oscilloscope 16

12 Conducted interference measurement set-up Connect directly the test output of the LISN/CDN to the oscilloscope EMI/EMC debugging with a moder oscilloscope 17

13 Conducted interference measurement Conducted Emission using LISN 9 khz 1 MHz EN55015Q EMI/EMC debugging with a moder oscilloscope 18

14 RTx PreCom Main GUI EMI/EMC debugging with a moder oscilloscope 19

15 RTx PreCom Limit Line Viewer / Editor Limit Lines are edited in Notepad EMI/EMC debugging with a moder oscilloscope 20

16 RTx PreCom Report Generator Reports can be saved as RTF and then imported into Word for further processing / formatting. EMI/EMC debugging with a moder oscilloscope 21

17 RTx PreCom Screen Copy Utility EMI/EMC debugging with a moder oscilloscope 22

18 EMI Voltage Test: Measurement Examples (using ENV216 LISN) Test Receiver Spectrum Analyzer Oscilloscope EMI/EMC debugging with a moder oscilloscope 23

19 EMI Current Test: Measurement Examples (using EZ-17 current probe) Test Receiver Oscilloscope EMI/EMC debugging with a moder oscilloscope 24

20 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 25

21 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 26

22 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 27

23 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 28

24 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 29

25 Radiated inteference measure EMI/EMC debugging with a moder oscilloscope 30

26 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 31

27 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 32

28 FFT as Basis for EMI Debugging with Oscilloscopes Conventional FFT Implementation on a Scope Time Domain Frequency Domain x(t) Dt = 1/F s F max = F s /2 S(f) S(f) Data acquisition t Windowing FFT f 1 f 2 f Zoom (f 1 f 2 ) f 1 f 2 Display f Record length T Df = 1/T Disadvantages: Time domain settings define frequency domain Zoom in frequency domain does not give more details Correlated Time-Frequency Analysis not possible EMI/EMC debugging with a moder oscilloscope 33

29 FFT on the RTO Spectrum Analyzer Use Model ı Use model: Frequency domain controls time domain Time domain parameters (record-length / sampling Time Domain Zoom happens here before the FFT! 500 MHz center, 10 MHz span: Fs = 1 GS/s vs 20 MS/s x(t) F s =2B Data acquisition t HW Zoom (DDC) NCO LP rate) automatically changed as necessary ı Downconversion FFT (DDC) zooms into frequency range before FFT Largely reduced record length, much faster FFT 500 MHz center, 10 MHz span: 1 GHz vs 20 MHz sampling frequency Decimation Windowing FFT S(f) B=f 2 -f 1 f 1 f 2 Display f Frequency Domain Record length T Df = 1/T EMI/EMC debugging with a moder oscilloscope 34

30 What if we combine time and frequency domain? Overlap FFT comes into play Record length 10GS/s 18.96ns/div 5 us/div ksamples FFT 1 FFT 2 FFT N Max frame count limit N = N max Frame coverage up to here ~440 1 FFT FFTs (persistance disabled) Advantages: Analyse time-dependend spectrum Conventional (non-overlapping) FFT looses information due to windowing overlapping allows to capture everything Limit No of frames to ensure fast FFT processing Note: FFT processing starts from the left! EMI/EMC debugging with a moder oscilloscope 35

31 Gated FFT in the RTO Practical Time-Frequency Analysis Gated FFT: 50% overlap (default setting) One complete Time-Domain capture Key Feature for EMI Debug! EMI/EMC debugging with a moder oscilloscope 36

32 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 37

33 Measurement Consideration: Sensitivity Ability to detect weak Signals EMI tends to be weak and near field probes have low gain, the oscilloscope needs to be able to detect small signals over its full bandwidth 1mV/div Low Noise and High Sensitivity at Full Bandwidth EMI/EMC debugging with a moder oscilloscope 38

34 Signal to Noise and ENOB Higher ENOB => lower quantization error and higher SNR => Better accuracy ı ADC-Picture Single-core monolithic 10GS/s ADC vs Multiple ADCs in Single chip > 7 ENOBs! High Accuracy without using interleaving! EMI/EMC debugging with a moder oscilloscope 39

35 Signal to Noise and ENOB ı Effective Number of Bits (ENOB): A Number for Signal Fidelity ± ½ LDB Error Effective Bits (N) Quantization Levels Least Significant Bit V mv Ideal ADC vertical 8bits = 256 Quantatizing levels Quantatized Digital Level Sample Points Analog Waveforms RTO Ideal mv mv mv mv < 8 bits Effective Number of Bits! Offset Error Gain Error Nonlinearity Error Aperture Uncertainty And Random Noise ı Higher ENOB => lower quantization error and higher SNR Better accuracy EMI/EMC debugging with a moder oscilloscope 40

36 Signal to Noise >80 db EMI/EMC debugging with a moder oscilloscope 41

37 Important Scope-Parameters for EMI Debugging Parameter Record length Sample rate Coupling Vertical sensitivity Color table & persistence FFT Span / RBW Signal zoom & FFT gating Description Ensure that you capture enough >2x max frequency, start with 2.5 GS/s for 0 1 GHz frequency range 50 W for near-field probes (important for bandwidth) 1 5 mv/div is usually a good setting Easily detect and distinguish CW signals and burst Constant Span / resolution bandwidth factor ( ) for easy usage when changing frequency span Easily isolate spurious spectral components in time domain EMI/EMC debugging with a moder oscilloscope 42

38 Radiated interference measurement EMI/EMC debugging with a moder oscilloscope 43

39 Locating EMI Faults: First Steps There are many potential sources of EMI on a board. Before you can eliminate an EMI issue you must first identify it. General approach Start with the largest loop probe smaller loop probe stub probe EMI/EMC debugging with a moder oscilloscope 44

40 Observe the Spectrum While Scanning With a Near-Field Probe I) General Approach ı Wide Span scan fundamental of interfering signals are usually lower than 1GHz, a span of <1GHz is sufficient as a start EMI/EMC debugging with a moder oscilloscope 45

41 Observe the Spectrum While Scanning With a Near-Field Probe I) General Approach ı Wide Span scan fundamental of interfering signals are usually lower than 1GHz, a span of <1GHz is sufficient as a start ı Identify abnormal spurious or behavior and its location while moving the probe around EMI/EMC debugging with a moder oscilloscope 46

42 Observe the Spectrum While Scanning With a Near-Field Probe I) General Approach ı Wide Span scan fundamental of interfering signals are usually lower than 1GHz, a span of <1GHz is sufficient as a start ı Identify abnormal spike or behavior and its location while moving the probe around ı Narrow down to smaller span and RBW, change to smaller probe for better analysis EMI/EMC debugging with a moder oscilloscope 47

43 Identifying EMI Through Signal Analysis Understand the DUT Known frequency source (clock and etc.) Possible harmonic frequencies Frequency & power of switching power supply emissions Identify miscellaneous periodic waves *Take into consideration of technique used such as Spread Spectrum Clocking, frequency hopping and etc. Causes of EMI ı EMI is often caused by the switching of signals, e.g. power supply, clocks, memory interface, etc. This is referred to as narrowband interference and generally occurs at very specific frequencies related to components on your board. EMI/EMC debugging with a moder oscilloscope 48

44 Identifying EMI by Frequency Content Understanding the expected signals and their harmonics, analyze possible interference sources in the frequency range of interest Signal Harmonics EMI/EMC debugging with a moder oscilloscope 49

45 Debugging EMI Using a Digital Oscilloscope Summary ı The modern oscilloscope with hardware DDC and overlapping FFT is capable of far more than a traditional oscilloscope ı EMI Debugging with an Oscilloscope enables correlation of interfering signals with time domain while maintaining very fast and lively update rate. ı The combination of synchronized time and frequency domain analysis with advanced triggers allows engineers to gain insight on EMI problems to isolate and converge the solution quickly. ı Power Supply design choices have a large impact on EMI emissions, frequency and time techniques can help unravel the mystery. EMI/EMC debugging with a moder oscilloscope 50

46 Debugging EMI Using a Digital Oscilloscope Thank you EMI/EMC debugging with a moder oscilloscope 51