RF101: EMC Diagnostics Sven De Coster CN Rood Bases on presentation by Steve Stanton, Product Planner, Source/Analyzer Product Line
Agenda Introductions Historical perspective Historical problems and methods The new problems Basics of EMC and EMI testing What does testing look like Acronyms, standards bodies, testing basics EMC Filter and detector definitions and effects Examples using a Real Time Spectrum Analyser in EMI diagnostics 2
RF101: EMC Diagnostics Historical Perspective
EMC Historical Perspective Spark-gaps, huge bandwidths and nobody cared about EMC until there were > 1 transmitters Broadcast transmissions and the rise of the electric society Many sources of EMI (motors, generators, cars, broadcasts) History of the problem: If I can t hear it or see it, does it matter? Current regulations intended to minimize audio and video problems Infrequent interference is allowed Momentary infrequent noise DOES matter to modern systems Packet based systems lose a whole packet and may need to resync Current measurements may be within specification, but cause your own system to fail from internal interference 4
What s the new problem? Switching Power Supply Switching Power Supply CPU Graphics Processor LCD Display Clock Generators Memory 802.15.1 802.15.1 WPAN WPAN Bluetooth 802.11 WLAN Other 802.3ae WPAN Ethernet NFC 802.16e WiMax I/O Control HDD Keyboard DVD Quad-band Multi-mode Cellular Cellular Phone 802.15.3 802.15.3a WPAN WPAN Clock Generators GPS Broadcast Video DVB-H MediaFLO T-DMB ISDB-T Modern system may include multiple noise sources, intentional radiators and multiple receivers in close proximity Transient noise can cause interference with integrated communications in a design Designs can meet regulatory EMI requirements but still not work correctly 5
What s the new problem? Automotive Electronic Applications Source: CVEL Automotive
However, the old problems must still be solved Standards Bodies define receivers in terms of Frequency range Resolution bandwidth Detectors and averaging Accuracy, sensitivity and dynamic range Requirements vary by geography and application CISPR, ANSI, TELEC and MIL standards may apply Comparable results require agreed-upon tools and methods 7
RF101: EMC Diagnostics Basics of EMC and EMI testing
EMC? What does that even look like? Electromagnetic Compatibility: an electronic or electrical product shall work as intended in its environment. The electronic or electrical product shall not generate electromagnetic disturbances, which may influence other products, and shall tolerate interference from other devices. Sounds simple, but EMC must be considered and tested during design, and products must pass many international standards Failure to comply means you can t sell your product, or face penalties Failing EMC testing after the product is designed is a major problem, and companies spend (a lot of) money to make sure it doesn t happen Increasingly, the problem is interference between devices in your own product, not interference from the outside This means your product doesn t work, and it s your fault. 9
Classes of test Emissions DUT must not interfere with other devices Conducted and Radiated tests are done T&M focus is on measurement of signals that come from the DUT Susceptibility DUT must operate in the presence of other devices that produce interference Other radios, computers, electrical motors, radars Power line transients, lightning Conducted and Radiated tests are done T&M focus is on creating interfering signals, and measuring them to make sure they meet standards 10
Emissions testing: Conducted and Radiated Conducted Testing Uses Line Impedance Stabilization Network (LISN) to separate line voltage from interference for measurement Standards are set to avoid the DUT from interfering on the power line Frequency ranges generally from 10 Hz to 30 MHz Radiated Testing DUT radiation measured with antenna or close-field probe. Turntable may be used to capture peaks from all physical orientations of the DUT Standards are set to avoid the DUT from interfering due to radiated emissions Frequency ranges generally from 9 khz to 1 GHz, often extending to 26.5 GHz and beyond 11
EMC in the product life cycle Design Design for EMC, evaluate/diagnose boards as they are developed pre-certification of prototype products followed by diagnoses of problems and fixes to design Certification of final products 12
Standards bodies define tests The level measured by a receiver or spectrum analyzer of any noncontinuous signal will depend upon the measurement bandwidth used Frequency ranges are defined Bandwidths and (filter) shapes are defined (resolution >< noise BW!) Frequency Range Reference BW (6 db) 9 khz to 150 khz (Band A) 200 Hz 0.15 MHz to 30 MHz (Band B) 9 khz 30 MHz to 1000 MHz (Bands C and D) 120 khz 1 GHz to 18 GHz (Band E) 1 MHz Table 1. Measurement Bandwidth versus Frequency specified by CISPR 16-1-1 Frequency Range Bandwidth (6dB) 10 Hz-20 khz 10, 100, and 1000 Hz 10-150 khz 1 and 10 khz 150 khz-30 MHz 1 and 10 khz 30 MHz-1GHz 10 and 100 khz 1-40 GHz 0.1, 1.0 and 10 MHz Frequency Range Bandwidth (6dB) 30 Hz 1 khz 10 Hz 1 khz-10 khz 100 Hz 10 khz-150 khz 1 khz 150 khz-30 MHz 10 khz 30 MH-1GHz 100 khz Above 1GHz 1 MHz Table 2. Bandwidths versus frequency specified for peak, average and RMS detectors by ANSI C63.2 Table 3. Bandwidths versus Frequency specified by Mil-STD-461E 13
Measurement settings: bandwidth effects Analyzer with selectable -3 db (RBW) and -6 db filter definitions, 1 db/division Random noise measured with 100 khz filters. -3dB, 100 khz response in yellow, -6dB, 100 khz response in blue. The power difference is 1.54 db, in close agreement with the theoretical value. 10*Log 10 (BW1/BW2), or 10*Log(71/100)=-1.5dB difference from using wrong BW 14
Common questions from EMC engineers Does a spectrum analyzer have CISPR peak, CISPR Average and Quasi-peak filters? these are often selectable in the trace function Does a spectrum analyzer have Mil-461 filters? these are often selectable in the RBW shape control Can a spectrum analyzer do limit testing using my antenna or probe? external correction factor tables can be stored and recalled limit testing can be done with the spurious measurement Can a spectrum analyzer generate automatic reports? Not all spectrum analyzers can do this, but often tables of failing frequencies and amplitudes can be generated with spur measurement Is a spectrum analyzer a CISPR-compliant receiver? No. Only a receiver with special preselectors for low-frequencies can meet the CISPR requirements. 15
Measurement settings: Peak, Average and QP Detectors Detectors were designed to place emphasis on frequently occurring signals that would annoy a listener or viewer of broadcast communications Now that communications are bursted and digital, these detectors no longer measure the effect of EMI on communications very well, but regulations are very slow to change Originally, the QP detector really was a RC circuit and a voltmeter- now it s implemented digitally Characteristics 9 khz-150 khz ( Band A) 0.15 MHz to 30 MHz ( Band B) 30 MHz to 1000 MHz ( Bands C and D) Bandwidth (6dB) 0.2 khz 9 khz 120 khz Detector charge time 45 ms 1 ms 1 ms Detector discharge time 500 ms 160 ms 550 ms Time constant of critically damped meter 160 ms 160 ms 100 ms Sin R1 S1 S2 C R2 16 The Quasi-Peak Detector and Associated Voltmeter
Measurement settings: QP detector and meter response Calculated response of the QP detector and and meter to pulse stimuls Characteristics 9 khz-150 khz ( Band A) 0.15 MHz to 30 MHz ( Band B) 30 MHz to 1000 MHz ( Bands C and D) Bandwidth (6dB) 0.2 khz 9 khz 120 khz Detector charge time 45 ms 1 ms 1 ms Detector discharge time 500 ms 160 ms 550 ms Time constant of critically damped meter 160 ms 160 ms 100 ms 17 Characteristic of quasi-peak detector versus frequency specified in CISPR 16-1-1 and ANSI C63.2
Measurement settings: Detector and meter response Average or QP+ Meter is always Peak measurement Measured CW power are equal for Average, QP and Peak detectors Peak Response QP Response 8 us PW, 10 ms rep. rate signal 18
Measurement settings: video filter Video filtering was the original trace smoothing technique to reduce variations in signals Specified off or not used for all but TELEC Widely used for many other SA applications Sometimes yields faster smoothing compared to waveform averaging Has the disadvantage of no intermediate results compared to waveform averaging Required by many legacy measurements, and preferred by many SA users Standards VBW Requirements Analyzer VBW setting CISPR VBW not used Maximum value or disabled TELEC VBW = RBW or VBW 3*RBW VBW=RBW or disabled MIL Greatest value or not used Maximum value or disabled Video bandwidth requirements specified for EMI measurements 19
Radiated Emissions and the RTSA, Advantages and Limitations Digital Phosphor Technology (DPX) is key to transient troubleshooting Frequency Mask Trigger (FMT) and capture great for diagnosis For some measurements, a Real-Time Spectrum Analyser (RTSA) is faster Some pre-certification and certification labs might want an RTSA for diagnostics, but unlikely to make their own system around it More likely candidate for a real-time spectrum analyzer is the designer who must troubleshoot their design before going to these (pre-)certification labs 20
Standards, Compliance, Pre-compliance and Diagnostics: Where RTSA s Fit To meet commercial standards, certified test results are required Not suited Pre-compliance tests can use uncertified sites and cost less than a full compliance test Problems are found earlier in the design stages, when fixes are relatively cheap Diagnostics is when the design engineer attempts a fix and needs to see what effect it had without doing a new pre-compliance or compliance test measurements are relative to previous results (before and after the fix) done in the development lab, or in a screen room or screen box might use close-field probes for evaluation of fixes Relative before and after measurement made to see if the problem was solved 21
Question: Do you do EMI measurements? What type of EMI measurements are you making? Certified: look for an (expensive) certification reciever or hire an (expensive) EMI expert at a certification lab Diagnostics: consider real-time spectrum analysis to shorten your design cycle and troubleshoot problems fast, before you go for certification Pre-certification produce spurious graphs and tables basic precertification making difference measurements as you change design elements Diagnostics probably not your only use of a Spectrum Analyzer make manual scans for checking on how your design changes will affect your final results, using the right filters and detectors find your transient EMI problem faster and better than anything else 22
An example of EMI diagnostics Embedded system with frequent hard-drive access during some modes of operation Transient EMI missed in peak scan with swept analyzer (yellow trace), found after 1 minute of Max-hold (blue trace) while DUT was cycled through disk-cache operation. Infrequent transient discovered with DPX after 5 seconds. The red areas are frequently-occurring signals, and the blue and green portions are transients. 23
Capture with frequency mask trigger, then fully analyze 24
RF101: EMC Diagnostics Example Applications an conclusion
Example Applications: Automotive Hybrid/Electric Vehicle Pain Point: Need a Spectrum Analyzer that can discover all the emissions for inverter motor in Hybrid/Electric vehicles, esp. the transient emissions, that cause interference to equipments, like Digital TV/radios, ECUs, Car Navigation/GPS system Conventional SA and VSA can not show all the transients Advantage of Real-Time Spectrum Analysis: Digital Phosphor (DPX) helps to discover all the transient emissions in real-time Frequency Mask Trigger (FMT) and real-time spectrogram greatly improved the troubleshooting productivity by reducing the test time from days to hours DC to 20MHz Base Band with DANL at less than -100dBm at 100kHz RBW captures low frequency inverter noise
Example Applications: Consumer Electronics Digital Camera Pain Point: Need a Spectrum Analyzer that can discover all the emissions, esp. the transient emissions, that cause interference to other modules on PCB, WLAN channels and GPS receiver Conventional EMC Compliance Tester/Reciever can not give full insights on all the transients Advantage of Real-Time Spectrum Analysis: DPX helps to discover all the transient emissions in real-time FMT and Real Time spectrogram greatly improves troubleshooting productivity Wide Acquisition Band (110MHz) can discover any signal anomalies in 2.4GHz ISM band Built in QP Detector and CISPR filters helps with conventional EMC pre-compliance tests
Conclusions A Real-Time Spectrum Analyser is a great diagnostic tool for EMI it s Digital Phosphor Technology (DPX) and Frequency Mask Trigger (FMT) makes the difference signals have changed, and having the filters and detectors is not enough Hopping, bursting and modulated signals that cause very low response to average or QP detectors are present in many designs They may even be missed by a peak detector if they are very infrequent, or shorter than the detector s attack specification These signals might pass a compliance test, but could cause problems in your own equipment or others DPX is the way to find and diagnose these signals DPX Density Trigger and Frequency Mask Trigger is the way to capture and fully analyze these signals Thank you! 28