Western MI IEEE Meeting
3-25-15
EMI Instrument Trends
CISPR-Ave and CISPR-RMS Detectors
Time Domain Scan Introduction
Instruments for EMI

Why two instruments for the same application?
-
ESR
Europe developed around EMI receivers
US market developed around Spectrum Analyzers
FCC written more for spectrum analyzers
CISPR specifies receivers
FSW
February 2012 | CISPR 16 – FFT-based measuring receiver | 2
FSH
Spectrum Analyzers for EMI
 Spectrum analyzer for EMI
- Speed….. Very fast initial look at emitters
- Quick feedback on changes to DUT
- Common, already in most labs
- Usable for other tests (spectral mask, transmitter / receiver quality tests,
antenna pattern measurement….)
 If used for EMI Tests, be aware
- Major Differences in spectrum analyzers before ~ 2004
- If using older SA (i.e. HP8566B or 8568B, FSE, ESIB)
- 1001 points only, sub ranging span is necessary
- Others only offered 501 meas points
- Newer analyzers offer 8000 - 36,000 measurement points
February 2012 | CISPR 16 – FFT-based measuring receiver | 3
Spectrum Analyzers for EMI

Frequency Accuracy of SA
- 500-1000 pts is far too course for EMI work
- Zoom in on emitter, what happens on screen?
- Rule-of-thumb: Need meas point at ½ RBW spacing

Example for RE102
- 200-1000 MHz range with 100 kHz RBW and 15mS dwell
- ½ of RBW = 50 kHz resolution required
- 800 MHz span / 50 kHz = 16,000 meas pts
- Even modern SA subrange 200-600 and 600-1000 MHz
- Set sweep time to 8000 pts x .15 mS = 1.2 sec min
February 2012 | CISPR 16 – FFT-based measuring receiver | 4
Samples and Measurement Pts
samples
Freq error
RBW
RBW
Integration of samples
Peak Displayed as
Measurement
Point
detector
Peak
QP
QP
Ave
Ave
•
QP
peak
peak
RMS
detector
Display Point 1
RMS
Display Point 2
Point amplitude is detector value, Point freq is reported in center
February 2012 | CISPR 16 – FFT-based measuring receiver | 5
Spectrum Analyzers for EMI
Conclusions ?
⇒ Even modern SA require user intervention for EMI
- Step size calculation for measurement pts
- Dwell time x meas points = sweep time setting
- Zero span mimics receiver function of tune / dwell
⇒ EMI procedure with spec an
 pick small span
 zoom in on measured peak
 center emission
 activate QP if needed
 record results
 repeat for next span
February 2012 | CISPR 16 – FFT-based measuring receiver | 6
Test Receivers for EMI
 Receivers allow direct programming of
- Frequency Span (start / stop)
- RBW Filter and detector
- DWELL TIME at each measurement point
- FREQUENCY INCREMENT (step size independent of RBW)
 Receivers
- adjust measurement points depending on span
- often gathers 30,000 – 100,000+ measurement points
- give proper frequency resolution when set
according to standard being used (no calculations)
February 2012 | CISPR 16 – FFT-based measuring receiver | 7
Receiver Measurements
•
Required Measurement Points using Rule-of-thumb Step size ≤ ½ RBW
Frequency Range
CISPR / FCC
Res BW
(6 dB)
Span
Min Freq
Resolution
Min # points
calculation
9 kHz – 150 kHz
200 Hz
~ 140 kHz
100 Hz
1,400
150 kHz – 30 MHz
9 kHz
~ 30 MHz
4.5 kHz
6,667
30 MHz – 1 GHz
120 kHz
970 MHz
60 kHz
16,167
1 GHz – 40 GHz
1 MHz
40 GHz
500 kHz
80,000
Frequency Range
RE101 / RE102
Res BW
(6 dB)
Span
Min Freq
Resolution
Min # points
calculation
30 Hz – 1 kHz
10 Hz
~ 1 kHz
5 Hz
200
1 – 10 kHz
100 Hz
9 kHz
50 Hz
180
10 – 250 kHz
1 kHz
240 kHz
500 Hz
480
250 kHz – 30 MHz
10 kHz
~ 30 MHz
5 kHz
6000
30 – 1000 MHz
100 kHz
~ 1 GHz
50 kHz
20,000
1 - 18 GHz
1 MHz
17 GHz
500 kHz
34,000
18-40 GHz
1 MHz
22 GHz
500 kHz
44,000
February 2012 | CISPR 16 – FFT-based measuring receiver | 8
Measurement Points Example
120
100
80
60
40
20
0
30M
50M
70M
100M
200M
300M
500M
700M
1G
Level [dBµV]
57.00
50.00
40.00
30.00
20.00
10.00
0.00
79.94M
85M
90M
95M
Frequency [Hz]
100M
109.63M
2012 | CISPR 16 –
FFT-based
receiversample
| 9
Example: February
TR (green)
vs.
SAmeasuring
(blue)
points
Test Receivers for EMI

Conclusion
⇒ Receiver incorporates additional control parameters
- STEP SIZE between measurement point
- DWELL TIME at each measurement point
- # of measurement points as necessary for accuracy

Time Penalty ?
- Test time more dependent on detector and EUT, not
measurement speed of instruments
- New scan modes eliminate any time penalty
February 2012 | CISPR 16 – FFT-based measuring receiver | 10
Receiver vs. Spectrum Analyzer Hardware
Both use super heterodyne down-conversion
Full
Spectrum
RF
Full Spectrum
RF
(9 kHz-3 GHz)
Preamp
Mixer
Stages
IF (RBW)
Filters
IF Hz
M
0
Preselection
Mixed
Spectrum RF
(3.5 GHz)
Filtered
Spectrum RF
(2
Attenuator
Filtered
Spectrum
RF
(2-8 MHz)
)
Digital Conversion
- Grey boxes show receiver
only hardware or functions
Local Oscillator
3.4-6.6 GHz
Detectors
Display
Markers
Limit lines
Trace evaluation
- Preselection improves selectivity (vital to mixer overload protection)
- Preamp improves sensitivity
- Firmware tools built specifically for EMI work
February 2012 | CISPR 16 – FFT-based measuring receiver | 11
Best Instrument for EMI?

Pros and Cons of Each
+ SA is faster for initial preview (but zoom in necessary)
+ SA can also be used for RX and TX measurements
+ TR can program required EMI parameters without
calculations or workarounds (less chance for errors)
- TR has little use outside EMI, expensive unit for one use
- SA needs special considerations when using QP detector
- SA sub-ranging & zooms negate any speed advantage for EMI
- SA frequency / amplitude accuracy easily skewed by
improper settings and interpretation
February 2012 | CISPR 16 – FFT-based measuring receiver | 12
Pre-Selection Filtering
Preselection is a hardware filter bank with switches
• Needed to reduce the total signal power present at the mixer
• Not likely available for spectrum analyzers
• Specified for EMI due to very large and very small signal
amplitudes encountered
• Critical for conducted emissions and OATS work
Mixer stage
Pre-selection
V(f)
V(f)
B2
B1
f
February 2012 | CISPR 16 – FFT-based measuring receiver | 13
Preselection Filtering

Preselector is a “tracking” RF filter
- ALL RF power (noise & signals) go into mixer
- high amplitude signals outside displayed span can
overload the instrument , compress or intermodulate

Cure: preselection / band filtering of signals
- SA may not warn of RF or IF overdrive
- Signals outside display ruin amplitude reading
- Allows zoom on low amplitude signals near high strength signals
- Dynamic range of instrument used for signals of interest
February 2012 | CISPR 16 – FFT-based measuring receiver | 14
Overdrive and Preselection
MARKER 1
1.000272533 GHz
Ref 0 dBm
*Att
20 dB
RBW 3 MHz
VBW 10 MHz
SWT 10 ms
0
Marker 1 [T1 ]
-43.41 dBm
1.000272533 GHz
Marker 2 [T1 ]
-54.36 dBm
1.501204189 GHz
-10
1 PK*
CLRWR -20
-30
-40
1
-50
2
-60
-70
-80
-90
+10 dBm signal at 500 MHz causing overdrive
-100
Start 400 MHz
February 2012 | CISPR 16 – FFT-based measuring receiver | 15
141.6135906 MHz/
Stop 1.816135906 GHz
A
Overdrive and Preselection
START FREQUENCY
600 MHz
Ref 0 dBm
*Att
20 dB
RBW 3 MHz
VBW 10 MHz
SWT 10 ms
0
Marker 1 [T1 ]
-43.41 dBm
1.000272533 GHz
Marker 2 [T1 ]
-54.58 dBm
1.501204189 GHz
-10
1 PK*
CLRWR -20
-30
-40
1
-50
2
-60
-70
-80
-90
Moving overload off screen won’t clear overload
-100
Start 600 MHz
February 2012 | CISPR 16 – FFT-based measuring receiver | 16
121.6135906 MHz/
Stop 1.816135906 GHz
A
Overdrive and Preselection
Ref
0 dBm
*Att
0
20 dB
RBW 3 MHz
VBW 10 MHz
SWT 10 ms
Marker 1 [T1 ]
-62.14 dBm
1.000272533 GHz
Marker 2 [T1 ]
-63.57 dBm
1.501204189 GHz
-10
A
1 PK*
CLRWR -20
-30
-40
PS
-50
-60
1
2
-70
-80
Activating Preselector clears overload by filtering the fundamental
-90
-100
Start 600 MHz
February 2012 | CISPR
16
measuring
121
.–6FFT-based
135906
MHz/receiver | 17 Stop 1.816135906 GHz
Quasi-Peak Detector

Quasipeak; Compliance vs Pre-compliance
- QP is an attempt to quantify annoyance factor
- Factors: amplitude, frequency, pulse repetition
- Requires special RBWs for accurate calculation

Quasipeak on Spectrum Analyzers
- Dwell time (per measurement point) at least 1 second
- zero span each measurement point
- sweep with QP trace active – 32,325 second sweep time
- QP NEVER higher than PK, increase sweep time if found
- QP results ~ 30 dB lower than peak for
pulse rates 100 Hz – 1 Hz
- SA need ~40 dB RF attenuation for QP & pulsed signals
- mixer dynamic range / VSWR requirements of CISPR-16-1
February 2012 | CISPR 16 – FFT-based measuring receiver | 18
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CISPR 11: Industrial, scientific and medical (ISM) radio-frequency equipment Electromagnetic disturbance characteristics - Limits and methods of measurement.
CISPR 22: Information technology equipment - Radio disturbance characteristics - Limits and
methods of measurement
CISPR 24: Information technology equipment - Immunity characteristics - Limits and methods
of measurement.
CISPR 12: Vehicles, boats and internal combustion engine driven devices - Radio disturbance
characteristics - Limits and methods of measurement for the protection of receivers except
those installed in the vehicle/boat/device itself or in adjacent vehicles/boats/devices.
CISPR 25: Vehicles, boats and internal combustion engines - Radio disturbance
characteristics - Limits and methods of measurement for the protection of on-board receivers"
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CISPR 14: Electromagnetic compatibility - Requirements for household appliances, electric
tools and similar apparatus - Part 1: Emission / Part 2: Immunity - Product family standard.
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CISPR 16: Specification for radio disturbance and immunity measurement apparatus
and methods
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Part 1: Radio disturbance and immunity measuring apparatus
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Part 2: Methods of measurement of disturbances and immunity
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Part 3: Reports and recommendations of CISPR
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Part 4: Uncertainties, statistics and limit modeling
February 2012 | CISPR 16 – FFT-based measuring receiver | 19
IT / ISM
autos
appliances
and tools
meas
devices
Other EMI Detectors
 RMS and Peak Detectors
- RMS for ultra wide band, dwell time critical for integration
- Peak is “safest detector”: fast enough to see most signals
even if instrument settings are not “optimum”
 CISPR Average & CISPR RMS Detector
- C-Ave responds to “intermittent, unsteady & drifting narrow
Band disturbances” equivalent to a peak power meter
- C-RMS responds to signals that interfere with digital
communication systems like WCDMA, Tetra, DECT, DVB
February 2012 | CISPR 16 – FFT-based measuring receiver | 20
CISPR Ave Detector
 CISPR Ave detector implementation
- uses a “meter simulating network”
- 160 mS time constant in CISPR bands A & B (9 kHz – 30 MHz)
- 100 mS time constant in CISPR bands C & D (30 MHz – 1 GHz)
Digital Conversion
Mixed
Spectrum RF
(3.5 GHz)
Mixer
Stages
Detectors
Display
Markers
Limit lines
Trace evaluation
IF
(20 MHz)
IF (RBW)
Filters
Envelope
Detector
Meter Simulating
Network
Local Oscillator
3.4-6.6 GHz
February 2012 | CISPR 16 – FFT-based measuring receiver | 21
CISPR Ave Detector
 CISPR Ave weighting for pulsed signals
February 2012 | CISPR 16 – FFT-based measuring receiver | 22
CISPR RMS Detector
 C-RMS (RMS-average) protects digital communication
- digital cellular, Tetra, DAB, DVB-T, DECT
- QP overvalued signals / Ave undervalued signal impact
- Implements a Combo RMS / linear average detector
Digital Conversion
Mixed
Spectrum RF
(3.5 GHz)
Mixer
Stages
IF
(20 MHz)
IF (RBW)
Filters
Detectors
Display
Markers
Limit lines
Trace evaluation
RMS
Detector
10 dB/decade
decrease
Linear
Average
Detector
Peak
meter
Decrease 20 dB/
decade + meter
constant
For low repetition
pulses Fp < 10 Hz
Local Oscillator
3.4-6.6 GHz
February 2012 | CISPR 16 – FFT-based measuring receiver | 23
CISPR RMS Detector
C-RMS behavior (applicable to continuous disturbances)
- Unmodulated sinewave signals (CW)
⇒ All detectors yield same values
- Gaussian Noise
⇒ C-RMS reads ~1dB higher than ave
⇒ 6 dB lower than QP (i.e. in band C & D)
⇒ 10 dB lower than PK
- Impulsive Noise
⇒ C-RMS reads higher than Ave, Lower than QP
February 2012 | CISPR 16 – FFT-based measuring receiver | 24
CISPR RMS Detector
RMS+Average weighting detector compared to existing detectors
(example as proposed for Bands C and D)
Weighting
Factor/dB
70
Average
RMS-AV
Quasi-Peak
Peak
60
RMS-AV
50
20 dB/decade
40
30
corner frequency
10 dB/decade
20
10
fp/Hz
0
1
10
100
1000
10000
100000
February 2012 | CISPR 16 – FFT-based measuring receiver | 25
1000000
Instrument and Standards Update
Time Domain Scans for EMI
February 2012 | CISPR 16 – FFT-based measuring receiver | 26
FFT Type Receivers- Can You Use Them?
l Amendment 1 to CISPR 16-1-1 (3rd Ed.)
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Use of FFT-based measurement instruments for compliance measurements
Specific requirements for FFT-based measuring instruments
The standard was published on 21 June 2010
l Applicability
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CISPR 13:2001 (Radio + TV)
CISPR 32:2012 (Multimedia)
CISPR 15:201x (Lighting)
CISPR 12 and 25 (Automotive)
CISPR 11 and 22
MIL-STD 461G
Applicable since 21.06.2010
Applicable since 30.01.2012
Applicable since 2012
Applicable since 2013
Allowed, but not required
Likely will be expressly allowed
February 2012 | CISPR 16 – FFT-based measuring receiver | 27
CISPR 16-1-1 A1 (3rd Ed.)
Measurement
receiver
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CISPR 16-1-1
compliant
measurements
Definition of “measuring receiver” added:
“instrument such as a tunable voltmeter, an EMI receiver, a spectrum
analyzer or an FFT-based measuring instrument, with or without
preselection, that meets the relevant parts of this standard”
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Specific requirement for FFT-based measuring instruments
“for EMI measurements, FFT-based measuring instruments shall sample
and evaluate the signal continuously during the
measurement time”
February 2012 | CISPR 16 – FFT-based measuring receiver | 28
CISPR 16 – FFT-based measuring receivers
FFT-based receivers – digital signal processing

Time domain
Temporal sampling of the filtered signals with
high sampling rate/resolution
Frequency domain
Frequency range to be measured is
sub-divided in consecutive frequency
segments and filtering
F(s) f(t)



Discrete Fourier transform (DFT)
Signal transformation of the filtered signals
from time domain to frequency domain
Frequency domain
Merging the spectral distributions of all partial
frequency ranges
February 2012 | CISPR 16 – FFT-based measuring receiver | 29
FFT Errors – Leakage Effect
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Convolution with window function yields wider spectrum
i.e. shows additional spectral components
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Sidelobes (referred to as leakage effect)
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These sidelobes should be suppressed by at least 40 dB
A suitable windowing reduces the leakage effect (Gauss, Kaiser-Bessel)
Rectangular window and magnitude of the Fourier transform 1)
Gaussian window and magnitude of the Fourier transform, σ=2
Sidelobes when using rectangular window or Gaussian window
1) Tilman Butz, Fouriertransformation fuer Fußgaenger, ISBN 978-3-8351-0135-7
February 2012 | CISPR 16 – FFT-based measuring receiver | 30
1)
FFT Errors – Picket Fence Effect
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The FFT calculates a discrete line spectrum at the frequency bins
If the sampled sine wave signal is at a frequency that doesn’t align with
a calculated frequency point an amplitude error appears
The amplitude error is known as “picket fence effect”
Like stepped-frequency scan with wide IF bandwidth vs step size
Fixed with smaller step size in frequency domain (i.e 1/4 RBW)
time domain
frequency domain
window width
February 2012 | CISPR 16 – FFT-based measuring receiver | 31
FFT Errors – Single Pulse Errors
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Measurement times must be long enough to capture single pulses
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Sample/calculate process must be gapless during the meas time
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Without time domain overlap amplitude / detection problems
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FFT Calculation overlap of >75%
in the time domain is necessary
to meet the pulse amplitude
specification of CISPR 16-1-1
February 2012 | CISPR 16 – FFT-based measuring receiver | 32
FFT Errors – Pulse Sequences
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0% overlap
25% overlap
75% overlap
90% overlap
Overlapping also
fixes pulse
sequence
amplitude errors
Example shows
the recalculated
IF signal for
different overlapping factors
February 2012 | CISPR 16 – FFT-based measuring receiver | 33
Minimizing the FFT Errors
Time-Domain Scan versus Stepped Scan
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R&S instruments provide
both scan methods using
the same hardware and
firmware
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Measurement was done
using a pulse generator for
CISPR bands C and D
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Overall frequency
response (Detector =
Max.Peak) shows that the
differences between the
two scan modes are
negligible
<0.5 dB
Trace 1: Time-domain scan (blue)
Trace 2: Stepped frequency scan (black)
February 2012 | CISPR 16 – FFT-based measuring receiver | 34
Incredible Speed of FFT Scans
CISPR Measurement Times FFT vs stepped scan
Automotive
February 2012 | CISPR 16 – FFT-based measuring receiver | 35
Summary: Benefits of FFT / Time Domain Scans
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Huge time savings vs conventional frequency (stepped) scans
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QP, CISPR-AV, RMS-AV are applicable in time-domain scan modes
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Plus still have classic modes to compare if in doubt
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Preselection preserves the full dynamic range for band of interest
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Measurement time up to 100 s without any gaps
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UMOD chip still allows zoom on any time window inside the capture
Measurement of pulses without significant error
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90% overlap (Auto Pulse) of the window function and gapless sampling
February 2012 | CISPR 16 – FFT-based measuring receiver | 36