EMC Training - Volta

EMC Training

Ing Angelo Cereser

[email protected]

Mobile: 335 57 88 293

Dott Mirko Bombelli

[email protected]

Mobile: 335 12 36 792

mailto:[email protected]

mailto:[email protected]

Agenda

Introduzione alle misure EMI Terminologia; precompliance verso full compliance

Setup di misura: emissioni radiate e condotte

CISPR 16-1-1 & MIL461F (Cenni)

L’analizzatore di spettro per le misure EMI

Time Scan mode Differenti metodi di scansione ( swept, stepped, time domain )

Approccio veloce al precompliance

Real Time Analysis Definizione di Real Time , Real Time operation , Overlap processing

Agenda


Setup di misura: emissione radiate e condotte






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 all the requirements of CISPR

16-1-1 (response to a CISPR pulse gen), a

qualified open area test site or semi

anechoic chamber and an antenna tower

and turntable to maximize EUT signals.

Precompliance Conducted Emission Testing set-up

Precompliance Radiated Emission Testing set-up

Compliance EMI receiver requirements

A CISPR 16-1-1 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

Receiver requirements above 1 GHz

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).

MIL STD 461F

• Spectrum Analyzer use allowed (and commonly used)

- need to ensure measurement linearity (avoid overloads)

- need to have sufficient sensitivity (may need preamp)

• Requires MIL Bandwidths

• Requires Peak Detector

• +/- 2dB amp accuracy, +/- 2% frequency accuracy

• Dwell times specified in document

Agenda








Theory of Operation

• Swept Spectrum Analyzer Block Diagram

Pre-Selector

Or Low Pass

Input Filter

Crystal

Reference

Oscillator

Log

Amp

RF input

attenuator mixer

IF filter

(RBW)envelope

detector

video

filterlocal

oscillator

sweep

generator

IF gain

Input

signal

ADC,

Display &

Video

Processing

RF Section ADC

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

FFT

All Digital IF” Advantages

Digital IF Improves Amplitude Accuracy

Input

Connector

Down-

conversionIF

Gain

IF

FilterLog

Amp

Video

Filter

RF Input

Attenuator2 dB Steps

Pre-selector

Log ADC

ADC DSP

Digital IF improves Amplitude Accuracy:

• Ref Level switching uncertainty (IF gain)

− Level correction digitally synthesized

• RBW filter switching uncertainty

− RBWs all digitally synthesized

• Display scale fidelity (Log Amp)

− Log response & display scaling digitally synthesized

Frequency

DependentFrequency

Independent

Amplitude

Uncertainty

N9038A

Receiver

Analog IF

(older

receivers)

Ref Level

Switching0dB <= +/- 1dB

RBW

Switching+/- .05dB <= +/- .5dB

Display Scale

Fidelity+/- .15dB <= +/- .85dB

EMI Receiver Block Diagram ( Keysight MXE )

Input 1

Input 2

Attenuation

Transient

Limiter

RF Preselector

Analog IF

Filter

Pre-amp

ADC

Digital IF

Filter

Digital Log Amp

Digital Detectors

FFT

Swept vs. FFT

MXE

RF Pre-selection (RF input filtering)

Purpose of RF pre-selection

– Help to prevent overload by reducing total energy at input mixer

– RF preselector tracks the center frequency of the EMI receiver

– The bandwidth of the RF preselector is wider than the widest RBW used

Useful in measuring broadband signals

Types of filters used in RF pre-selectors

– Low-pass, Band-pass and High-pass

– Fixed and Tracking

Broadband

signals

Narrow

band

signals

Wider RF Preselector Filter BW = Reduced Impulse Overload Protection

• Examples* : @10MHz: 20 log (35MHz/9.5MHz) = 11.3dB

• @ 500MHz: 20 log (200MHz/ 50MHz) = 12dB

• *Note: Above calculations using 6dB BW ratios, not impulse BW ratios

• Results provide approximate values of required input attenuation

Down-

conversion

RF

Preselector

Receiver RF Section

Vp

Impulse BW

BWi

Τ= pulse

width

Vmax = Vp Τ BWi

Input pulse

Max Pulse voltage

into mixer is

proportional

to RFPS filter

impulse BW (BWi)RF Input

Attenuator

RF Preselector Bands for MXE

Pre-compliance

Compliance

N6141A EMI Measurement Application

GW Instek

low cost

solution

Keysight CXA entry-level Keysight MXE N9038A

CXA EMC analyzer precompliance

USB LAN/USB

EMSCAN Scanner

MXE EMI Reciever

• Excellent accuracy and sensitivity

- 0.82 dB @ 1 GHz

- -163 dBm @ 1 GHz

• Full Cispr 16.1.1 Compliance

- -two inputs for conducted and radiated

• Real Time Analyzer

- Up to 85 Mhz RTBW

- Time Domain Scan Capability

- Upgradable up to 44Ghz

20 Hz to 3.5Ghz or

8.4Ghz or 26.5Ghz

or 44GHz

20 Hz to 1 GHz

surge protected

Agenda








Customer challenge

• Need for SPEED

– DUTs that require short measurement time (ex. motor starter)

– Test MORE devices

– Shorter turn-around-time

• Depends On:

– Scan type (Stepped, Swept, Time Domain)

– Resolution Bandwidth

– Dwell Time

– RF Preselector

– Other?

Methods to EMI Scanning

• Stepped Scan

– Slowest method

– LO moves for every bin

– Must re-tune LO each time

• Swept Scan

– Slow (slightly faster than Stepped)

– LO re-tunes once each sweep

• Time Domain Scan (TDS)

– Very fast

– Highly overlapped FFT (>90%)

– Alternate scan method allowed by CISPR 16

Time Domain Scan (TDS)

• What is “Time Domain Scan”- A new way to do Frequency scanning

- Swept scans, Stepped scans, now Time Domain scans

• FFT-based scan

- uses ~ 90% overlap (in time) to ensure amplitude accuracy

for measurements of both CW and Impulsive signals

•Allowed by CISPR 16, but not required.

- Internal Automotive industry testing specifications require

Time Domain

33

How Time Domain Sweep Saves Time

frequency

am

plit

ude

frequency

am

plit

ude

Receiver FFT BWReceiver Resolution BW

Swept or Stepped

Frequency Scan

Time Domain

Frequency Scan

Have to dwell at

each RBW

Only have to dwell for each

FFT BW (multiple RBWs)FFT BW

• Classic FFT is critically sampled – windows are contiguous

• What happens to impulsive signals?

• Signals that fall between windows are attenuated by window edges

• Impulsive signals not detected or detected with “amplitude scalloping”

• How to solve this problem?

Window Effects and Sample Rate

• Answer is to add overlap windowing

• Equivalent to increasing sampling rate out of the decimated downconverters

• Impulsive signals no longer can fall between widows

• “Amplitude scalloping” reduced

• More overlapping => less amplitude errors

Oversampling before FFT

Time

Domain

Scan

Frequency

Domain Scan

CISPR Band MXE MXE

30MHz–1GHzPeak det. 10ms. dwell

RBW =120kHz

3 pts/RBW~ 12 s 242 sec

smooth scan

150kHz–30 MHzPeak det 100ms. dwell

RBW = 9kHz

2 pts/RBW~ 13 s 664 sec

smooth scan

Time Domain improves sweep time

Page 37

Agenda








Customer Challenge

Quickly detect and locate non-cooperative modern

signals which may be intermittent, be of short duration,

spread spectrum, have low power and/or low energy.

What is “Real Time” Analysis?

•General Definition of Real Time

– Measurement operations where all signal samples are used in calculating

measurement results of some kind (usually spectrum)

•Real Time Bandwidth (RTBW)

– The widest analysis bandwidth where an analyzer can maintain real time

operation

– Duration of maintaining real time operation is not specified; it may assumed to

be short term or long term or unlimited

•Current Usage for Signal Analyzers

– A spectrum or FFT analyzer having a signal processing path where most or all

samples, even at wide bandwidths, are used to create a spectral display or to

trigger signal measurement or acquisition (sometimes both)

What is Real Time?

Gap free

• no dead time between acquisitions; all sampled data is processed; process is continuous

Consistent speed

• all hardware implementation of FFT spectrum generation – not subject to Windows’ task interruptions

What is Real Time?

High speed measurements

• many thousands of FFT generated spectrums per second, vastly exceeding software FFT speed

High speed displays

• combine large numbers of measurements to form responsive, insight-producing displays

Real Time Operation

•In Real Time Operation the Analyzer’s Processing (CALC) is

Fast Enough to Keep Up with All Data Samples

•CALC Time Includes FFT or Power Spectrum, Averaging, Display

Updates, etc.

However some data

may still be “lost”

Overlap Processing

•If Processing is Faster than Sampling, Perform Additional FFTs With Partially-New

Time Records as Samples Come In

Avoid Loss of Data Due to Windowing

Accurate Amplitude Measurements of Short Duration Signals

Overlap 0%

Overlap 50% Processor Idle

Window

Function

Swept tuned spectrum analyzer

Pros:

- Excellent dynamic range

- Very fast sweep for very large span

- Precisely control sweep time

- Easy to measure line spectrum of pulse

signal

-

Cons:

- Could miss intermittent signal contents

- Very slow when RBW:SPAN is too small

-

Snap shot FFT spectrum analyzer

filterattn IF A/D FFT

mixer

LO Sample scheduler

Pros:

- Not missing signal content within

information bandwidth

- Very fast update at narrow RBW

- Provides digital demodulation

Cons:

- Relative slow under very large bandwidth

- Cannot precisely control sweep time

- When signal is larger than its instantaneous

bandwidth, stitching is required (could miss

change of signals)

Real Time Spectrum Analyzer

filterattn IF A/D FFT

mixer

LO Gap free sampling

/buffering

Pros:

- Provide 100% POI to capture signal within

real time bandwidth

- Only way to measure transient and

dynamic signals

- IQ streaming

- Ideal for RF pulse signal characterization

-

Cons:

- Real time bandwidth is limited

- Typically it is less accurate comparing with

GP SA

Probability of missing signals

Real time BW

Freq

Time

Swept tuned SA Snapshot FFT SA Real time SA

RTSA applications

In traditional SA mode, it is hard to

find the interfering signal buried

inside downlink carrier.

The narrow band signal (center:

877MHz, bandwidth:12 kHz )

In RTSA, density display can clearly

identify the embedded signal at

877MHz

Embedded signal

RTSA Enhancements

Available on Xseries

• Enabled in both FMT and Level Triggers

• Trigger only on signals that are less than,

greater than, inside, or outside defined time

durations

Interfering Zigbee and

WLAN - Overlapping

signals in the frequency

domain can be resolved

by using TQT

Isolated WLAN

signal

Isolated Zigbee

Summary

3.57 us Probability of Intercept

• Best performance for measuring intermittent signals

Widest BW & Freq

• 85 MHz bandwidth and 44 GHz frequency range to analyze large chunks of the spectrum

Two in one

• Eliminate the need for a specialized or dedicated instrument by adding real-time capabilities to the MXE EMI Reciever

Per documentazione su prodotti ed applicazioni EMI/EMC visitare il sito

http://www.keysight.com/find/EMC

THANK YOU!!

http://www.keysight.com/find/EMC

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EMC Training - Volta