EMC Measurements. Jan Sjögren Electronic Measurements Group Agilent Technologies Page 1. EMC seminar

Transcription

1 EMC Measurements Jan Sjögren Electronic Measurements Group Agilent Technologies Page 1

2 Day Agenda 8.45 REGISTRATION 9.00 Introduction 9.15 EMC Back to Basics EMC - What is it and why should you care? EMC compliance issues you need to be aware of. How to make EMC pre-compliance Measurements Lunch and Demo Stations EMSCAN: Very-Near-Field solutions for Far-Field Problems 1 Hour in a chamber or 1 Second with EMSCAN Closing Words Page 2

3 Agenda Introduction to EMI measurements Terminology Measurement system (antenna, LISN, receiver, etc.) Detectors European and international standards Pre-compliance measurement Measurements of radiated emissions Measurements of conducted emissions Measurements of immunity (EMS) Measurement Setup Anechoic chambers versus OATS (Open Area Test Site) Agilent solutions Introducing the new Agilent MXE EMI receiver Full Compliance Using the Agilent X-Series analyzers for EMI pre-compliance measurements Application Software Complete solutions through our partners Page 3

4 What is EMC? Electromagnetic Compatibility (EMC): The ability of equipment to operate in its electromagnetic environment without introducing intolerable disturbances into other devices. Combination of Interference and Immunity. Electromagnetic Interference (EMI): Electromagnetic energy emanating from one device which causes another device to have degraded performance. Electromagnetic Immunity (Susceptibility, EMS): Tolerance in the presence of electromagnetic energy (Performance degradation due to electromagnetic energy). Page 4

5 Definitions EMI Electromagnetic interference (aka emissions) EMC Electromagnetic Compatibility EMS Electromagnetic susceptibility (aka Immunity) Page 5

6 Sources of Electromagnetic Interference Natural Sources Lightning Sun Spots Unintentional emitting products Power lines Motors (mixers, hair dryers etc) Lighting, appliances Devices that intentionally emit signals Most computers Hand held communication devices Radar, transceivers, broadcast equipment etc Page 6

7 EMI measurement system Page 7

8 Pre-compliance vs. Full compliance measurements Pre-compliance measurements Evaluate the conducted and radiated emissions of a device using correct detectors and bandwidths before going to a test house for compliance testing Full Compliance measurements Full compliance testing requires a receiver that meets the requirements of CISPR part (for commercial) or MIL-STD-461 (for military), a qualified open area test site or semi anechoic chamber and an antenna tower and turntable to maximize EUT signals. EMI receivers require a pre-selector at lower frequencies to limit the input energy and maintain sufficient dynamic range to meet the CISPR 16 requirements. Page 8

9 Compliance EMI receiver requirements A CISPR receiver must have the following functionality in the range 9 khz - 18 GHz: A normal +/- 2 db absolute accuracy CISPR-specified resolution bandwidths (-6 db) Peak, quasi-peak, EMI average, and RMS average detectors Specified input impedance with a nominal value of 50 ohms; deviations specified as VSWR Be able to pass product immunity in a 3 V/m field Be able to pass the CISPR pulse test (implies pre-selector below 1 GHz) Other specific harmonic and intermodulation requirements Page 9

10 CISPR Pulse Generator for Testing the QP response Purpose of the Schwarzbeck generator Schwarzbeck Pulse Generator Establish the reference repetition rate for band A, B, C and D using QPD The repetition rate can be varied between 1000 Hz and an isolated pulse The relative equivalent level can be adjusted Page 10

11 Receiver requirements above 1 GHz Above 1 GHz regulations require: 1 MHz bandwidth for measurements No quasi-peak detector No CISPR pulse test, meaning no additional pre-selector required excellent sensitivity According to current FCC regulations, the maximum test frequency is the fifth harmonic of the highest clock frequency for an unintentional radiator (for example, computers without wireless connectivity) and the tenth harmonic for an intentional radiator (such as a cellular phone or wireless LAN). Page 11

12 What is an EMI Receiver? Let s begin with a spectrum analyzer Spectrum Analysis Display and measure amplitude versus frequency for RF & MW signals Separate or demodulate complex signals into their base components (sine waves) Page 12

13 Overview Types of Tests Made Modulation EMC Noise Distortion Page 13

14 Theory of Operation Swept Spectrum Analyzer Block Diagram RF input attenuator mixer IF gain IF filter (RBW) envelope detector Input signal Pre-Selector Or Low Pass Input Filter local oscillator Log Amp video filter sweep generator Crystal Reference Oscillator ADC, Display & Video Processing Page 14

15 RF Pre-selection (RF input filtering) Purpose of RF pre-selection Help to prevent overload by reducing the total energy at the input mixer The RF preselector tracks the center frequency of the EMI receiver The bandwidth of the RF preselector is wider that the widest RBW used Useful in measuring broadband signals Narrow band signals Broadband signals Page 15

16 Traditional Spectrum Analyzer Scalar analysis Digitizing the video signal Product detector loss of phase information Classic superheterodyne swept spectrum analyzer 16

17 Digital IF Spectrum/Signal Analyzer Vector data CAN be preserved (mag/phase or I/Q) Digitizing the IF Signal Some troublesome operations and conversions are now fast, accurate DSP 17

18 Specifications Resolution: RBW Type Determines Sweep Time 8563E Analog RBW PSA Digital RBW PSA FFT RBW 280 sec 134 sec 13.5 sec Page 18

19 Speed Improvements Nominal speed comparison, PSA example: Benchmark PXA PSA Useful comparisons highly specific, many factors PXA mode switching typically faster than PSA Speed improvement Preset (*RST) 28 ms 168 ms 6x Marker peak search 6.5 ms 78 ms 12x Local Update 13 ms 17 ms 1.3x CF Tune and Transfer (4-5GHz) 109 ms 186 ms 1.7x Remote sweep and trace transfer 18 ms 30 ms 1.67x Where speed is critical, consider modifying measurement routines to include features such as list sweep 19

20 Modern spectrum analyzer Resolution BW Selectivity or Shape Factor 3 db 3 db BW 60 db 60 db BW Selectivity = 60 db BW 3 db BW Determines resolvability of unequal amplitude signals Page 20

21 Specifications Resolution: RBW Type and Selectivity ANALOG FILTER Typical Selectivity Analog 15:1 Digital 5:1 DIGITAL FILTER RES BW 100 Hz SPAN 3 khz Page 21

22 Digital Filter Shape Better shape factor, biggest selectivity benefit for different signal levels Equivalent selectivity at a wider, faster-sweeping RBW digital filters swept an additional 3-4x faster 30 khz Digital Filter 22

23 CISPR Bandwidth Requirements Bandwidth -6dB -20dB Measurement Range CISPR Band CISPR Bandwidth 9 KHz 150KHz A 200 Hz 150 KHz 30 MHz B 9 KHz 30 MHz 1 GHz C/D 120 KHz > 1GHz E 1 MHz Page 23

24 CISPR Bandwidth Requirements, cont Band A filter Page 24

25 MIL-STD-461 Bandwidth Requirements Measurement Range -6dB Bandwidth 30Hz - 1 KHz 10 Hz 1 KHz -10 KHz 100 Hz 10 KHz KHz 1 KHz 150 KHz - 30MHz 10 KHz 30 MHz - GHz 100 KHz > 1GHz 1 MHz Page 25

26 Detectors: Convert IF Samples to Display Bins or Buckets Multiple simultaneous detectors Peak, Neg Peak, Sample Display points or buckets Peak Normal, Average, Neg Peak Volts Sample Neg Peak Screen Shot Detector 3types Time 26

27 Detectors Most radiated and conducted limits are based on quasi-peak detection mode. Page 27

28 Peak vs. Quasi-peak vs. Average V Peak Detection Quasi-Peak Detection Average Detection V time Peak Detection time Quasi-Peak Detection Average Detection Page 28

29 Peak QP Average Peak Detector Initially used Faster than QP and Average modes If all signals fall below the limit, then the product passes and no future testing is needed. QP For CW signal, Peak = QP Much slower by 2 or 3 order magnitude compared to using Peak detector Charge rate much faster than discharge rate the higher repetition rate of the signal, the higher QP reading Average Radiated emissions measurements above 1 GHz are performed using average detection Page 29

30 EMI Receiver Detectors (cont d) EMI Average Detection This is the response to a pulse by the average detector RMS Average Detection RMS-average weighting receivers employ a weighting detector that is a combination of the rms detector (for pulse repetition frequencies above a corner frequency fc) and the average detector (for pulse repetition frequencies below the corner frequency fc), thus achieving a pulse response curve with the following characteristics: 10 db/decade above the corner frequency and 20 db/decade below the corner frequency. Page 30

31 Modern Spectrum Analyzer Accuracy Some modern analyzers approach accuracy of power meter + sensor Even better for low-level signals, with narrower noise bandwidth and the benefit of frequency selectivity Some factors determining uncertainty: Input connector (mismatch) RF input attenuator Mixer and input filter (flatness) IF gain/attenuation (reference level) RBW filters Display scale fidelity Calibrator 31

32 Modern Spectrum Analyzer - Specifications Digital IF provides power meter like accuracy Page 32

33 Line Impedance Stabilization Networks (LISN) Purpose of a LISN: 1. Isolates the power mains from the equipment under test. The power supplied to the EUT must be as clean as possible. Any noise on the line will be coupled to the X-Series signal analyzer and interpreted as noise generated by the EUT. 2. Isolates any noise generated by the EUT from being coupled to the power mains. Excess noise on the power mains can cause interference with the proper operation of other devices on the line. 3. The signals generated by the EUT are coupled to the X-Series analyzer using a high-pass filter, which is part of the LISN. Signals that are in the pass band of the high-pass filter see a 50-Ω load. Page 33

34 LISN Page 34

35 Electrical Network 150 khz to 30 MHz Page 35

36 Transient Limiter The purpose of the limiter is to protect the input of the EMC analyzer from large transients when connected to a LISN. Switching EUT power on or off can cause large spikes generated in the LISN. Limiter LISN The Agilent 11947A transient limiter incorporates a limiter, high-pass filter, and an attenuator. It can withstand 10 kw for 10 μsec and has a frequency range of 9 khz to 200 MHz. The high-pass filter reduces the line frequencies coupled to the EMC analyzer. Page 36 DUT

37 Field Strength Unit Radiated EMI emissions measurements measure the electric field. The field strength is calibrated in dbμv/m. Pt = total power radiated from an isotropic radiator Pd = the power density at a distance from the isotropic radiator (far field >λ/2π) P d Pt 4 r 2 E R 2 Pt 4 r 2 R 120 [ohm] Free Space Impedance 2 E P d R r E Pt 30 r [V/m] Page 37

38 Field Strength and Antenna factors Radiated EMI emissions tests measure the electric field. The field strength is calibrated in dbμv/m. Antenna factors is the ratio of the electric field (V/m) present at the plane of the antenna versus the voltage out of the antenna connector. Log units: AF(dB/m) = E(dBμV/m) - V(dBμV) E(dBμV/m) = V(dBμV) + AF(dB/m) Notes: Antenna factors are not the same as antenna gain. dbμv = dbm Page 38

39 Broadband antenna examples Double ridged horn antennas Biconical antenna Log Periodic antenna Hybrid log periodic Hybrid log periodic Page 39

40 EMC Regulations An Overview Page 40

41 Standard Setting Institutions CISPR (International Special Committee on Radio Interference) IEC* 174 Technical committees and subcommittees CENELEC European standards organization TC77 (Technical Committee 77) deals with EMC FCC Federal Communication Commission ANSI American National Standards Institute *IEC International Electrotechnical Commission Page 41

42 Frequency Bands for Conducted and Radiated Emission Mil-STD Radiated (RE101, RE102) Mil-STD Mil-STD Conducted (CE106) or Mil-STD Radiated (RE103) Mil-STD Conducted (CE101, CE102) Commercial CISPR Radiated FCC Radiated CISPR, FCC conducted 30Hz 9 khz 10 MHz 30 MHz 10 khz 18GHz To 40 GHz RE103 may be used as an alternative for CE106 when testing transmitters with their intended antennas. CE106 is the preferred requirement unless the equipment or subsystem design characteristics preclude its use. Page 42 Page 年 9 月 5 日星期一 Sun Tong

43 Who must comply with EMC Directive Manufacturers of electronic equipment such as: ITE (information technology equipment) ISM (industrial, scientific medical) Broadcast receivers Household appliances and tools Luminaries and fluorescent lighting If a product does not fit into one of the above categories then it must follow the generic standard Page 43

44 National Regulations Summary for Radiated and Conducted Emissions CISPR FCC EN Description 11 Part 18 EN55011 ISM equipment 12 (SAE) EN55012 Vehicles off board rec. 13 Part 15 EN55013 Broadcast receivers 14 EN55014 Household appliances 15 EN55015 Luminaries (fluorescent lights) 16 Receivers/Methods 22 Part 15 EN55022 IT Equipment 25 EN55025 Vehicle on board rec. Page 44

45 European Norms example EN55014 (CISPR 14) This standard applies to electric motor-operated and thermal appliances for household and similar purposes, electric tools and electric apparatus. Limit line use depends upon the power rating of the item. EN55014 distinguishes between household appliances, motors less than 700W, less than 1000W and greater than 1000W. Limits for conducted emissions are 150 khz to 30 MHz, and limits for radiated emissions are 30 MHz to 300 MHz Page 45

46 MIL-STD 461 Bandwidths and Measurement Times Page 46

47 EMC Testing During Product Life Cycle Page 47

48 The Need for a Complete EMC Test Strategy Why Not Just Build the product then test it? The chances of passing compliance testing is less than 10% The cost of failure: Market window lost (Competitor beats you to market) Additional engineering time Cost of fixes to pass emissions Cost of retesting Page 48

49 EMI problem costs Breadboard/Design Prototype Production The Cost of EMI solutions as the project progresses Project development time line Page 49

50 Compliance Testing for Emissions 50

51 General Process for Making EMI Measurements Determine the country or countries in which the product will be sold which in turn identifies the regulatory agency. Select the limit lines to be tested to (conducted/radiated). Select the band to be used. Correct for transducer loses and amplifiers gains. Identify signals above the limit that must be evaluated. Zoom in on failed signal and perform quasi-peak or average measurements. Page 51

52 Conducted Emissions Measurements 1. Connect DUT to the test system 2. Set the proper frequency range 3. Load limit lines and correction factors for LISN and limiter 4. View the ambient emissions with DUT OFF 5. Switch on the DUT and find signals above limits by using peak detector 6. Measure all signals above limits with quasi-peak and average detectors Page 52

53 Page 53

54 The challenge of measuring radiated emissions Radiated Emissions are difficult to measure because of multiple dimensions (five) and the use of quasi-peak detection below 1GHz 5 -Time 1 - Azimuth 2 - Antenna Height 3 - Field Strength MHz MHz MHz 4 - Frequency Page 54

55 Examples of Test Facilities Open Area Test Site (OATS) Useful in low ambient signal environments GHz Transverse Electro Magnetic Cell (GTEM Cell) Used for smaller devices. Can be used for immunity and emissions. Page 55

56 GTEM Cell details RF output for emissions testing or RF input for immunity testing DUT Area Septum terminated in 50 ohms RF absorbers Page 56

57 Test Facilities (cont d) 10 Meter Semi Anechoic* Chamber This chamber uses 2 antenna towers, one for vertical and one for horizontal polarization. Uses a ground plan. Reverberation Chamber Uses a mode stirring tuner to generate a uniform field (no absorption material on the walls) *Anechoic material are made of carbon impregnated rubberized cones or ferrite tiles or both Page 57

58 Radiated Emissions Measurements 1. Connect the antenna to the EMI receiver and separate the antenna from the DUT as specified by the regulation requirements 2. Set the proper frequency range and bandwidth 3. Load limit lines and correction factors for antenna and cable. 4. With DUT OFF, measure the ambient emissions and store them 5. Switch on the DUT and find signals above limits by using peak detector (only those not present during the ambient scan). Rotate the DUT to maximize the emissions. 6. Measure all signals above limits with quasi-peak and average detectors Page 58

59 1. Select the measurement range Page 59

60 2. Load Corrections factors Amplitude at point circled Amplitude referenced to blue line Page 60

61 3. Load Limit line Circle indicates the position of the amplitude frequency pair Page 61

62 4. Scan for signals above the limits with peak detector Page 62

63 5. Quasi-peak and average measurements Page 63

64 Once EMC testing becomes part of the product strategy (THEN WHAT) Continue to use test houses at $$$$ per hour OR Build your own facility for M$ + Purchase and setup a precompliance system X-Series signal analyzer with N6141A /EMC app. LISN Antennas and tripod Page 64

65 Pre-compliance testing Approach Full Compliance Testing Accuracy At a fraction of the cost of full compliance testing Minimum Pre-compliance test system Pricing Product CXA Signal Analyzer to 7 GHz W6141A EMC application LISN Biconical Antenna Log Periodic Antenna Antenna Tripod Total Price Price 16.3k USD 4.1k USD 2.4k USD ~5k USD ~5k USD ~0.5k USD ~33.3k USD Page 65

66 Automation in Pre-compliance Measurements Reasons for Automation -Supplement skill and knowledge of the tester -Measurements repeatability -Results are presented in a common format -Reduce test time by automating setups Types of Automation -Internally executed application such as N6141A -PC based applications Software Available -Techcelerant, TILE from ETS Lindgren, TDK RF Solutions, Radimation from DARE Page 66

67 Pre-compliance Conducted Emissions Setup X-Series Signal Analyzer To Mains LISN DUT With N6141A EMC App Transient Limiter DUT power cord* *Keep the power cord short to avoid becoming an antenna Page 67

68 Pre-compliance Radiated Emissions Setup Perform testing in both the horizontal and vertical position 3 or 10 Meter distance DUT Ground Plane X-Series Signal Analyzer with N6141A EMC App The goal is to find and record the maximum emissions from the DUT by rotating the turn table, changing the polarization and the height of the antenna. Page 68

69 Troubleshooting Use the close-field probe to locate the sources of the radiated signals exceeding the limit lines Page 69

70 Immunity test setup Amplifiers Radiated Immunity 30 MHz 18 GHz HF-Switch Conducted Immunity 100 khz 1 GHz Page 70

71 Agilent Solutions Page 71

72 What is a CISPR Compliant Receiver CISPR is a subcommittee of the IEC CISPR is the document that defines the functionality of an EMI receiver Detectors Frequency response N9038A MXE EMI receiver is CISPR Compliant Page 72

73 EMI Receiver Requirements for Compliance Testing of Conducted and Radiated Emissions N9038A MXE Compliant receiver CISPR Hz, 9 khz, 120 khz (6 db) and 1 MHz (imp) bandwidths -Peak, Quasi-peak, EMI average, RMS average detectors -RF Pre-selection to meet CISPR pulse generator response -VSWR, 0dB and 10dB input attenuation -Amplitude Accuracy MIL-STD 461 -Peak detection only -MIL STD BWs (10 Hz, 100 Hz, 1 khz, 10 khz, 100 khz, 1 MHz) Page 73

74 What is the MXE EMI Receiver? The Agilent MXE is more than a CISPR compliant EMI receiver It is also an X-Series signal analyzer that can run a variety of measurement applications The MXE can evolve as technology changes X-Series signal analyzer CISPR 16 compliant EMI receiver Page 74

75 Agilent X-Series Signal Analyzers Multiple instruments in one box: Swept spectrum analyzer; FFT analyzer; Analog and digital modulation analyzer; Noise Figure analyzer EMI receiver Fastest signal analysis measurements Broadest set of applications and demodulation capabilities Upgradeable HW Most advanced user interface & world-class connectivity Page 75

76 All Digital IF Advantages RF Section ADC FFT IF/BB Section on ASIC Flexibility: RBW filtering in 10% steps Filters with better selectivity Multiple operation modes (Swept, FFT, VSA, NFA) Accuracy: Log conversion practically ideal No drift errors; increased repeatability Speed: When Swept mode is slow, go FFT Page 76

77 Techniques for Reducing DANL, Improving Dynamic Range Reduce attenuation Add preamp Reduce RBW Add external filtering Better/shorter cables, connectors Move analyzer closer Time averaging (where possible, not measurement avg.) Measurement processing (take advantage of Moore s Law) Noise power subtraction/noise correction/nnc Noise floor extension (NFE) leverages deep knowledge of analyzer/circuit behavior 77

78 CW Signal Measured Near Analyzer Noise Floor Example: No noise subtraction or near noise correction Apparent Signal Actual S/N Displayed S/N CW Signal Ampl & Freq Axes Expanded This is fundamental, and often missed 78

79 Noise Floor Subtraction P obss+n = P obsn + P S P S = P obss+n P obsn Analyzer noise adds incoherently to any signal to be measured Power calculations are performed on a linear power scale (watts, not dbm) and results typically are shown in dbm 79

80 Noise Subtraction, Noise Floor Extension New technique NFE improves D.A.N.L. analyzer noise power calculated/subtracted real time No error 3 db error without NFE Improved noise floor or displayed average noise level 80

81 EMC Features standard in all X-Series Spectrum analyzers Limit Lines (2000 pts) Amplitude correction (2000 pts) sweep points Page Page 81 81

82 Option EMC in X-Series spectrum analyzer CISPR detectors (to latest spec) Quasi Peak EMI Average ( CISPR-AVG ) RMS Average ( CISPR-RMS ) EMI Bandwidths (CISPR & MIL STD) EMI Presets Tune & Listen Measure at Marker EMI Peak, EMI Average, and Quasi Peak measurements displayed together Page 82

83 W/N6141A EMC measurement application Full Featured Pre-compliance Application Available in all X-Series models Page 83

84 Corrections factors edit display Amplitude at point circled Amplitude referenced to blue line Page 84

85 Limit line edit display Circle indicates the position of the amplitude frequency pair Page 85

86 Auto-detect peaks Log Display Realtime Meters with any 3 Simultaneous Detectors Peak List Limit Delta Page 86

87 N6141A measurement: Frequency Scan with Log Display Meters tune to selected signal Page 87

88 N6141A measurement: Strip Chart Time record of zero span data scrolls to left Up to three different detectors Can be used to make click measurements Patent Applied For Click measurements are made on home appliances Page 88

89 Option EDP (Enhanced Display Package) for the SA Spectrogram Trace Zoom Zone Span Page 89

90 N6141A EMI Measurement Application PXA MXA Pre-compliance EXA Compliance CXA Agilent MXE N9038A

91 Agilent products for Immunity test (EMS) Signal generator Signal generator 9 khz 3 GHz, AM, FM, Phase, Pulse IQ Modulator, 40 MHz Mod.-BW N5181B, N5182B, N5183A 9 khz- 1,3, 6, 20, 40 GHz, AM, FM, Phase, Pulse, optional vector, 120 MHz Mod.-BW, step, sweep, USB-Power meter included Power meter/ Power sensors E441x, E191x, N8262, U200x 100 khz 40 GHz single channel, dual channel, USB, peak, envelope, pulse Accessories Directional Couplers, cables, Adapters, Switches etc. Page 91

92 Solution partners for EMC Complete solution: 1. Automation software 2. Chambers 3. GTEM 4. Antennas 5. Power amplifiers 6. Accessories Page 92

93 For more information about EMC solutions from Agilent please visit: Contacts: Jan Sjogren Signal Analysis and Generation Sales Specialist Agilent Contact Center Tel: Microlease (Agilent Authorized Technology Partner) Tel: Page 93