Improving EMI Accuracy

James YoungRohde & Schwarz

James YoungRohde & Schwarz

Improving the accuracy ofEMI emissions testing

Q&AQ&A

Who uses what for EMI?Who uses what for EMI?

CISPR, MIL-STD or Automotive?CISPR, MIL-STD or Automotive?

⇒ Spectrum Analyzers (SA)⇒ Spectrum Analyzers (SA)

⇒ Test Receivers (TR)⇒ Test Receivers (TR)

Software or front panel ?Software or front panel ?

Novice, Capable, Fluent or Expert ?Novice, Capable, Fluent or Expert ?

OverviewOverview

EMI Equipment comparisonEMI Equipment comparison

Making accurate measurementsMaking accurate measurements

⇒ RF / IF overload and Preselection⇒ RF / IF overload and Preselection

⇒ EMI Detectors and Filters⇒ EMI Detectors and Filters

⇒ Spectrum Analyzers (SA)⇒ Spectrum Analyzers (SA)

⇒ Test Receivers (TR)⇒ Test Receivers (TR)

⇒ Preamps, where and when⇒ Preamps, where and when

Spectrum Analyzers for EMISpectrum Analyzers for EMI


SA setup for EMI ExampleSA setup for EMI Example- Set Start freq, stop freq, RBW and detector from standard- Set Start freq, stop freq, RBW and detector from standard- Span of 1G-30MHz = 970 MHz / 1000 = 1 MHz resolution- Span of 1G-30MHz = 970 MHz / 1000 = 1 MHz resolution- x samples in RBW are stored, 500 or 1000 are displayed- x samples in RBW are stored, 500 or 1000 are displayed

- samples within RBW analyzed or weighted by the detector- samples within RBW analyzed or weighted by the detector

- QP “integrates” voltage in RBW, applies CISPR weighting- QP “integrates” voltage in RBW, applies CISPR weighting

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120Level [dBµV]

30M 50M 70M 100M 200M 300M 500M 700M 1G


QuestionQuestion

- What was wrong with the previous setup?- What was wrong with the previous setup?

AnswerAnswer- Frequency and amplitude accuracy depend on many samples falling within each measurement bin (also called display pixel).- Next “bin” will be 1 MHz away (nearly 10 x 120 kHz)!- Frequency resolution much too course for EMI- Solution?

- Frequency and amplitude accuracy depend on many samples falling within each measurement bin (also called display pixel).- Next “bin” will be 1 MHz away (nearly 10 x 120 kHz)!- Frequency resolution much too course for EMI- Solution?

30M 50M 70M 100M 200M 300M 500M 700M 1G


Example RevisitedExample Revisited

- Span of 970 MHz / 1001 = 1 MHz resolution- Span of 970 MHz / 1001 = 1 MHz resolution

- If using 120 KHz RBW, CISPR recommends 60 KHz “bin” points (17 x finer than 1 MHz)

- If using 120 KHz RBW, CISPR recommends 60 KHz “bin” points (17 x finer than 1 MHz)

- Solution: subrange in the span- Solution: subrange in the span

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120Level [dBµV]

30M 50M 70M 100M 200M 300M 500M 700M 1G

Frequency Accuracy of SAFrequency Accuracy of SA

- SA frequency resolution is far too course for EMI without sub-ranging the CISPR span

- SA frequency resolution is far too course for EMI without sub-ranging the CISPR span

- SA frequency accuracy when exploring peaksinfluenced by Span, RBW, VBW, marker accuracy

- SA frequency accuracy when exploring peaksinfluenced by Span, RBW, VBW, marker accuracy


Amplitude Accuracy of SAAmplitude Accuracy of SA- 6 dB (EMI) filters- QP and AVE detector times are observed- Data correction for system transducers- EUT specific timing issues are considered- Subranges set properly for sample #- RF and IF stages are not overloaded

- 6 dB (EMI) filters- QP and AVE detector times are observed- Data correction for system transducers- EUT specific timing issues are considered- Subranges set properly for sample #- RF and IF stages are not overloaded


- STEP SIZE between measurement bins- STEP SIZE between measurement bins

- DWELL TIME at each measurement bin- DWELL TIME at each measurement bin

⇒ SA lacks 2 control parameters for EMI⇒ SA lacks 2 control parameters for EMI

ConclusionConclusion

⇒ Sub-ranging and zero span is an attempt to make SA measure like TR

⇒ Sub-ranging and zero span is an attempt to make SA measure like TR

- Lacks dynamic range and overload protection (later slides)- Lacks dynamic range and overload protection (later slides)

Test Receivers for EMITest Receivers for EMI


Receivers for EMIReceivers for EMI

- Frequency Span (start / stop)- Frequency Span (start / stop)

- RBW Filter and detector- RBW Filter and detector

- DWELL TIME at each measurement point- DWELL TIME at each measurement point

- TR adjusts sample x and bins depending on span- TR adjusts sample x and bins depending on span

- Span / x = frequency resolution- Span / x = frequency resolution

- FREQUENCY INCRIMENT (step size independent of RBW) - FREQUENCY INCRIMENT (step size independent of RBW)

- x is often 16,000 – 100,000+- x is often 16,000 – 100,000+

Sample Points ExampleSample Points Example

Example: TR (green) vs. SA (blue) sample pointsExample: TR (green) vs. SA (blue) sample points

020406080

100120

30M 50M 70M 100M 200M 300M 500M 700M 1G

0.00

10.00

20.00

30.00

40.00

50.00

57.00Level [dBµV]

79.94M 85M 90M 95M 100M 109.63MFrequency [Hz]

Samples and BinsSamples and Binssamples

Display BIN

detector

peak

QP

Ave

RMS

detector

peak

QP

Ave

RMSDisplay BIN

Integration of samplesPeak Lost

Freq error

QPPeak

• Bin amplitude is detector value, Bin freq is reported in center• SA has 1001 bins, TR accesses 100,000 bins (from memory)

RBW

RBW

Receiver MeasurementsReceiver Measurements

Frequency Range 6-dB Bandwidth Step Size(<1/2 RBW)

# of measBins

150 kHz to 30 MHz 9 kHz 4 kHz 7,463

30 MHz to 1 GHz 120 KHz 50 KHz 19,400

• CISPR 16 recommends Step size ≤ RBW / 2

80M 85M 90M 95M 100M 110M

Frequency [Hz]

VS


- Time dependant on detector and EUT, notmeasurement speed of instruments

- Time dependant on detector and EUT, notmeasurement speed of instruments

Time Penalty ?Time Penalty ?

⇒ TR incorporates EMI control parameters⇒ TR incorporates EMI control parameters


- STEP SIZE between measurement bin- STEP SIZE between measurement bin

- DWELL TIME at each measurement bin- DWELL TIME at each measurement bin

- # of measurement bins as necessary for accuracy- # of measurement bins as necessary for accuracy

Best Instrument for EMI?Best Instrument for EMI?

Pros and Cons of EachPros and Cons of Each

- SA can also be used for RX and TX measurements- SA can also be used for RX and TX measurements

- SA frequency / amplitude accuracy easily skewed by improper settings and interpretation

- SA frequency / amplitude accuracy easily skewed by improper settings and interpretation

- SA is faster for initial preview- SA is faster for initial preview

- SA sub-ranging negates any speed advantage over TR for EMI

- SA sub-ranging negates any speed advantage over TR for EMI

- TR has little use outside EMI, expensive unit for one use

- TR has little use outside EMI, expensive unit for one use

Which one to use?Which one to use?Use SA or TR to develop “hit list”Use SA or TR to develop “hit list”

Use SA or TR for maximizationUse SA or TR for maximization

TR is optimum for final (dwell time, step size and auto attenuator)

TR is optimum for final (dwell time, step size and auto attenuator)

30 MHz 1 GHz

dBµVdBµV

1 PKCLRWR

SGL

RBW 120 kHzMT 1 sPREAMP ONAtt 30 dB AUTO

100 MHz 200 MHz 300 MHz 400 MHz 500 MHz 600 MHz 700 MHz 800 MHz 900 MHz

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60

10 20 30 40 50 60 70 80 90

FREQUENCY 931.9200000 MHz

LEVEL QPK dBµV

10 20 30 40 50 60 70 80 90


LEVEL QPK dBµV

10 20 30 40 50 60 70 80 90


LEVEL QPK dBµV

FCC15RB

Date: 8.SEP.2003 14:13:12

Making accurate measurementsMaking accurate measurements

Overload protectionOverload protection

Detectors for EMIDetectors for EMI

PreampsPreamps

RBW Filters for EMIRBW Filters for EMI

Accurate MeasurementAccurate Measurement

Accuracy killersAccuracy killers

160 dB = 10e8 or 8 orders of magnitude160 dB = 10e8 or 8 orders of magnitude

EMC engineers don’t know what signalsthey are looking for initially

EMC engineers don’t know what signalsthey are looking for initially

Dynamic range of SA / TR is ~160 dBDynamic range of SA / TR is ~160 dB

- Overloads (RF and IF)- Incorrect detector settings- Preamplifiers improperly used- Improper RBWs

- Overloads (RF and IF)- Incorrect detector settings- Preamplifiers improperly used- Improper RBWs

RF OverdriveRF Overdrive

RF: Watch for harmonics of large signalsRF: Watch for harmonics of large signals

- Use attenuator to set mixer input level- Use attenuator to set mixer input level

Mixer Level

RF Attenuation sets mixer input level

Ref Level

Max Input LevelIn

put

1st

mix

er

RF Overload Example RF Overload Example

Example: amplified signal at 500 MHzExample: amplified signal at 500 MHz

Ref 0 dBm 496 MHz

A

496 MHz

1 SA

496 MHz

AVG

496 MHzRBW 3 MHz

496 MHz VBW 10 MHz 496 MHzSWT 10 ms

496 MHzAtt 10 dB

496 MHz*

496 MHz 496 MHz 496 MHz 496 MHz 496 MHz 496 MHz 496 MHz 496 MHz 496 MHz 496 MHz

Center 1 GHz

496 MHz

Span 2 GHz

496 MHz

200 MHz/

496 MHz

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496 MHz1

Marker 1 [T1 ] 3.03 dBm 496.000000000 MHz

2

Marker 2 [T1 ] -48.80 dBm 996.000000000 MHz

3

Marker 3 [T1 ] -48.60 dBm 1.500000000 GHz

MARKER 1

496 MHz

Date: 23.JUN.2004 20:33:37

IF OverdriveIF Overdrive

IF: Watch for overload flagsIF: Watch for overload flags

- Set IF gain using “ref Level”- Set IF gain using “ref Level”

Mixer Level

Ref Level sets IF Gain

Ref LevelIn

put

1st

mix

er

IF G

ain

- Use Ref Level to set IF Gain- Use Ref Level to set IF Gain

IF Overload ExampleIF Overload Example

Example: +6 dBm PulseExample: +6 dBm Pulse

1 AP

10 dB

CLRWR

10 dB

A

10 dB 10 dB 10 dB 10 dB 10 dB 10 dB 10 dB 10 dB 10 dB 10 dBRBW 3 MHz

10 dB VBW 10 MHz 10 dB

SWT 5 ms

10 dB

Ref 0 dBm

10 dB

Center 502.0534106 MHz

10 dB

Span 990.2160153 MHz

10 dB

99.02160153 MHz/

10 dB

Att 10 dB

10 dB*

10 dB

OVLD

10 dB

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10 dB

1

Marker 1 [T1 ] 6.13 dBm

502.053410569 MHz

RF ATTENUATION

10 dB

Date: 23.JUN.2004 20:55:20

Preselection FilteringPreselection Filtering

Preselector is a “tracking” RF filterPreselector is a “tracking” RF filter

Cure: preselect filtering of signals before RF or IFCure: preselect filtering of signals before RF or IF

- SA may not warn of RF or IF overdrive- SA may not warn of RF or IF overdrive

- IF overload won’t show on display - IF overload won’t show on display

- ALL RF power (noise & signals) go into mixer- ALL RF power (noise & signals) go into mixer

- high amplitude signals outside displayed span caninfluence amplitude and may be aliased

- high amplitude signals outside displayed span caninfluence amplitude and may be aliased

- Signals outside display ruin amplitude reading- Signals outside display ruin amplitude reading

Preselection SimplePreselection Simple

V(f)

f

B1

V(f)

B 2

Mixer stagePre-selection

Overdrive and PreselectionOverdrive and Preselection

Example: +10 dBm signal at 500 MHz causing overdriveExample: +10 dBm signal at 500 MHz causing overdrive

CLRWR

1.000272533 GHz

A

1.000272533 GHzRef 0 dBm 1.000272533 GHz

*

1.000272533 GHz

1 PK

1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHzAtt 20 dB

1.000272533 GHz*

1.000272533 GHz

141.6135906 MHz/

1.000272533 GHz

Start 400 MHz

1.000272533 GHz

Stop 1.816135906 GHz

1.000272533 GHzRBW 3 MHz

1.000272533 GHz VBW 10 MHz 1.000272533 GHzSWT 10 ms

1.000272533 GHz

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1.000272533 GHz

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Marker 1 [T1 ] -43.41 dBm 1.000272533 GHz

2

Marker 2 [T1 ] -54.36 dBm 1.501204189 GHz

MARKER 1

1.000272533 GHz

Date: 8.SEP.2003 13:03:46


Example2: Moving overload off screen won’t clear overloadExample2: Moving overload off screen won’t clear overload

CLRWR

600 MHz

A

600 MHzRef 0 dBm 600 MHz

*

600 MHz

1 PK

600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHzAtt 20 dB

600 MHz*

600 MHz

121.6135906 MHz/

600 MHz

Start 600 MHz

600 MHz

Stop 1.816135906 GHz

600 MHzRBW 3 MHz


600 MHz

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600 MHz

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Marker 1 [T1 ] -43.41 dBm 1.000272533 GHz

2

Marker 2 [T1 ] -54.58 dBm 1.501204189 GHz

START FREQUENCY

600 MHz

Date: 8.SEP.2003 13:04:13


Example3: Activating Preselector clears overload by filtering the fundamentalExample3: Activating Preselector clears overload by filtering the fundamental

CLRWR

1.000272533 GHz

A

1.000272533 GHzRef 0 dBm 1.000272533 GHz

*

1.000272533 GHz

1 PK

1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHz 1.000272533 GHzAtt 20 dB

1.000272533 GHz*

1.000272533 GHz

141.6135906 MHz/

1.000272533 GHz

Start 400 MHz

1.000272533 GHz

Stop 1.816135906 GHz

1.000272533 GHzRBW 3 MHz

1.000272533 GHz VBW 10 MHz 1.000272533 GHzSWT 10 ms

1.000272533 GHz

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1.000272533 GHz

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Marker 1 [T1 ] -43.41 dBm 1.000272533 GHz

2

Marker 2 [T1 ] -54.36 dBm 1.501204189 GHz

MARKER 1

1.000272533 GHz

Date: 8.SEP.2003 13:03:46

CLRWR

600 MHz

A

600 MHzRef 0 dBm 600 MHz

*

600 MHz

1 PK

600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHz 600 MHzAtt 20 dB

600 MHz*

600 MHz

121.6135906 MHz/

600 MHz

Start 600 MHz

600 MHz

Stop 1.816135906 GHz

600 MHzRBW 3 MHz


600 MHz

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600 MHz

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Marker 1 [T1 ] -43.41 dBm 1.000272533 GHz

2

Marker 2 [T1 ] -54.58 dBm 1.501204189 GHz

START FREQUENCY

600 MHz

Date: 8.SEP.2003 13:04:13

CLRWR

A

Ref 0 dBm

*1 PK

Att 20 dB*

121.6135906 MHz/Start 600 MHz Stop 1.816135906 GHz

RBW 3 MHzVBW 10 MHzSWT 10 ms

PS

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Marker 1 [T1 ] -62.14 dBm 1.000272533 GHz

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Marker 2 [T1 ] -63.57 dBm 1.501204189 GHz

Date: 8.SEP.2003 13:04:47

PRF, Dwell time and DetectorsPRF, Dwell time and Detectors

EUT / Detector dwell time requirementsEUT / Detector dwell time requirements

- Must capture “worst case” emissions of EUT- Must capture “worst case” emissions of EUT

- Cycle time, modulation, and pulse repetition frequency may require extended dwell in each subrange (QP,AVE, RMS)

- Cycle time, modulation, and pulse repetition frequency may require extended dwell in each subrange (QP,AVE, RMS)

- Test Receivers include this parameter-Since tuning each bin, can dwell as long as necessary

- Spectrum Analyzers have a workaround-Zero Span is a way to trick SA into dwelling at tuned bin-Must do calculation since overall sweep time is controlled-Dwell time = sweep time / measurement bins

- Test Receivers include this parameter-Since tuning each bin, can dwell as long as necessary

- Spectrum Analyzers have a workaround-Zero Span is a way to trick SA into dwelling at tuned bin-Must do calculation since overall sweep time is controlled-Dwell time = sweep time / measurement bins

Detector SettingsDetector Settings

Quasipeak ???? Quasipeak ????

⇒ QP is an attempt to quantify a signalsImpact on a radio receiver (annoyance)⇒ QP is an attempt to quantify a signalsImpact on a radio receiver (annoyance)

Quasipeak restrictions Quasipeak restrictions

- Dwell time (per step or subrange) at least 1 second- Dwell time (per step or subrange) at least 1 second

- PRF issues increase dwell time requirements- PRF issues increase dwell time requirements

- Factors: amplitude, frequency, pulse repetition frequency- Factors: amplitude, frequency, pulse repetition frequency

Detector SettingsDetector Settings

Peak Detector Peak Detector

Average or RMS DetectorAverage or RMS Detector

- Peak gives “worst case”- Peak gives “worst case”

- Safest detector: Often fast enough to see most signals even if instrument settings are not “optimum”

- Safest detector: Often fast enough to see most signals even if instrument settings are not “optimum”

- Average detector used above 1 GHz for FCC and CE tests- Average detector used above 1 GHz for FCC and CE tests

- Watch RBW (1MHz or 120 KHz above 1GHz?)- Watch RBW (1MHz or 120 KHz above 1GHz?)

- dwell for at least 100 mS at each bin for proper integration- dwell for at least 100 mS at each bin for proper integration

- RMS for ultra wide band, dwell time critical for integration- RMS for ultra wide band, dwell time critical for integration

Detector Settings ExampleDetector Settings Example

Example: -40 dBm signal at 280 MHz measures with RMSExample: -40 dBm signal at 280 MHz measures with RMS

Ref -20 dBm Att 10 dB

CLRWR

A

50 MHz/Start 0 Hz Stop 500 MHz

RBW 120 kHz

SWT 175 ms

*1 RM

VBW 1 MHz

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Marker 1 [T1 ]

-49.64 dBm 280.000000000 MHz

Date: 23.JUN.2004 21:44:15

Detector Settings ExampleDetector Settings Example

Example2: Same -40 dBm but with Ave and same settingsExample2: Same -40 dBm but with Ave and same settings


CLRWR

A


RBW 120 kHz

SWT 175 ms

*1 RM

VBW 1 MHz

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Marker 1 [T1 ]

-49.64 dBm 280.000000000 MHz

Date: 23.JUN.2004 21:44:15


CLRWR

A


RBW 120 kHz

SWT 175 msVBW 1 MHz

*1 AV

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Marker 1 [T1 ] -56.89 dBm 280.000000000 MHz

Date: 23.JUN.2004 21:44:41

Detector Settings ExampleDetector Settings ExampleRef -20 dBm Att 10 dB

CLRWR

A


RBW 120 kHz

SWT 175 ms

*1 RM

VBW 1 MHz

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Marker 1 [T1 ]

-49.64 dBm 280.000000000 MHz

Date: 23.JUN.2004 21:44:15


CLRWR

A


RBW 120 kHz

SWT 175 msVBW 1 MHz

*1 AV

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Marker 1 [T1 ] -56.89 dBm 280.000000000 MHz

Date: 23.JUN.2004 21:44:41


CLRWR

A


*1 QP

RBW 120 kHzVBW 1 MHzSWT 175 ms

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Marker 1 [T1 ] -76.57 dBm 280.000000000 MHz

Date: 23.JUN.2004 21:45:04

Example3: Same -40 dBm but with QP and same settingsExample3: Same -40 dBm but with QP and same settings

Transducer correctionTransducer correction

- CISPR needed a way to eliminate effects of variability inchambers, antennas and cable losses

- CISPR needed a way to eliminate effects of variability inchambers, antennas and cable losses

- Standards require normalization of these effects to compare results to limit line

- Standards require normalization of these effects to compare results to limit line

Transducers and PRFTransducers and PRF

- Chamber ruled by Normalized Site Attenuation (NSA)- Chamber ruled by Normalized Site Attenuation (NSA)

- Transducers and connections used correction factors derivedfrom actual calibrations

- Transducers and connections used correction factors derivedfrom actual calibrations

Resolution Bandwidth FiltersResolution Bandwidth Filters

Unit dB V

A

SWT 5 ms

Ref Lvl

97 dB V

Ref Lvl

97 dB V

RF Att 20 dB

Center 100 MHz Span 1 MHz100 kHz/

2MA

RBW 100 kHz

VBW 10 MHz

IN11MA1MAX

2VIEW2VIEW 2MA1MA

0

10

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30

40

50

60

70

80

90

-3

97

6dB RBW

3dB RBW

PreampsPreamps

Preamps: When are they needed? Preamps: When are they needed?

- Generally needed above 7 GHz- Generally needed above 7 GHz

- Below 7 GHz ONLY if stringent limit line or long cables- Below 7 GHz ONLY if stringent limit line or long cables

Preamps: Where to put them?Preamps: Where to put them?

- Preamps amplify signal and noise- Preamps amplify signal and noise

- Real goal of preamp is PRESERVE signalto noise ratio (best at the antenna)

- Real goal of preamp is PRESERVE signalto noise ratio (best at the antenna)

- Low level signals require amplification at antenna, before signal is subjected to path loss of cables

- Low level signals require amplification at antenna, before signal is subjected to path loss of cables

PreampsPreamps

Preamp S/N Ratio examplePreamp S/N Ratio example

S N

S N S N

S N

S N S N

Preamp near EMI receiver

Preamp at antenna

Common Cables loss

½ dB per meter at 1GHz

3 dB per meter at 40 GHz

PreampsPreamps

Preamps Preamps

- Must have high gain & low noise figure (amp contributed noise)- 1-18 GHz gain around 30 dB with NF of 3.2 dB or less- 18-26 GHz gain around 35 dB with NF of 3.0 dB or less- 26-40 GHz gain around 50 dB with NF of 2.8 dB or less

- Must have high gain & low noise figure (amp contributed noise)- 1-18 GHz gain around 30 dB with NF of 3.2 dB or less- 18-26 GHz gain around 35 dB with NF of 3.0 dB or less- 26-40 GHz gain around 50 dB with NF of 2.8 dB or less

- Noise Figure equation states the 1st gain/loss encountered has the most impact on s/n ratio

- Noise Figure equation states the 1st gain/loss encountered has the most impact on s/n ratio

S NRF Thermal Noise (N0)

Noise contributed by preamp (NF)

PreampsPreamps

Know your Preamp overload range and behaviorKnow your Preamp overload range and behavior

- Know the preamp range (what is the max signal input without compression or damage)

- Know the preamp range (what is the max signal input without compression or damage)

- Must keep preamp in linear region- Must keep preamp in linear region

- Watch RF input levels to 1st mixer system check if unsure (variable attenuator)- Watch RF input levels to 1st mixer system check if unsure (variable attenuator)

- Non-wave guide antennas have a direct connection to the FET, watch static discharge

- Non-wave guide antennas have a direct connection to the FET, watch static discharge

PreampsPreamps


RF & IF OverloadsRF -> Harmonics IF -> If overload flag

Attenuator Ref Level

RF & IF OverloadsRF -> Harmonics IF -> If overload flag

Attenuator Ref Level

Preampsamplify at antenna know linear region below 1gz

system check (attenuator) static

Preampsamplify at antenna know linear region below 1gz

system check (attenuator) static

TR vs. SASpan Subranges step size resolution

dwell time overloading preselection

TR vs. SASpan Subranges step size resolution

dwell time overloading preselection

Documents

Improving EMI Accuracy