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
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RF101 EMC Diagnostics
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
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RF101 EMC Diagnostics
What’s the new problem?
Switching
Power Supply
CPU
Switching
Power Supply
Memory
Graphics
LCD
Processor
Display
802.15.1
802.15.1
WPAN
WPAN
802.11
WLAN
Bluetooth®
Clock
Generators
Other
802.3ae
WPAN
Ethernet
NFC
802.16e
WiMax ®
I/O
Control
HDD
Quad
- band
Quad-band
Multi-mode
Cellular
Cellular
Keyboard
DVD
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
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RF101 EMC Diagnostics
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
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RF101 EMC Diagnostics
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.
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RF101 EMC Diagnostics
Classes of test
Emissions
Susceptibility
– DUT must not interfere with
other devices
– 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
measurement of signals that
come from the DUT
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– Conducted and Radiated
tests are done
– T&M focus is on creating
interfering signals, and
measuring them to make
sure they meet standards
RF101 EMC Diagnostics
Emissions testing: Conducted and Radiated
Conducted Testing
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Radiated Testing
Uses Line Impedance Stabilization
Network (LISN) to separate line
voltage from interference for
measurement
DUT radiation measured with antenna or
close-field probe.
Standards are set to avoid the DUT
from interfering on the power line
Standards are set to avoid the DUT from
interfering due to radiated emissions
Frequency ranges generally from
10 Hz to 30 MHz
Frequency ranges generally from 9 kHz
to 1 GHz, often extending to 26.5 GHz
and beyond
Turntable may be used to capture peaks
from all physical orientations of the DUT
RF101 EMC Diagnostics
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
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RF101 EMC Diagnostics
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
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
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Frequency Range
RF101 EMC Diagnostics
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*Log10(BW1/BW2), or 10*Log(71/100)=-1.5dB difference from using wrong BW
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RF101 EMC Diagnostics
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.
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RF101 EMC Diagnostics
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
R1
S1
Sin
C
S2
R2
The Quasi-Peak Detector and Associated Voltmeter
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RF101 EMC Diagnostics
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
Characteristic of quasi-peak detector versus frequency specified in CISPR 16-1-1 and ANSI C63.2
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RF101 EMC Diagnostics
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
8 us PW, 10 ms rep. rate signal
QP Response
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RF101 EMC Diagnostics
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
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RF101 EMC Diagnostics
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
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RF101 EMC Diagnostics
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
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RF101 EMC Diagnostics
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
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RF101 EMC Diagnostics
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.
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RF101 EMC Diagnostics
Capture with frequency mask trigger, then fully analyze
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RF101 EMC Diagnostics
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!
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RF101 EMC Diagnostics