EMC Training. Ing Angelo Cereser Mobile:

Transcription

1 EMC Training Ing Angelo Cereser Mobile: Dott Mirko Bombelli Mobile:

2 Agenda Introduzione alle misure EMI Terminologia; precompliance verso full compliance Setup di misura: emissioni radiate e condotte CISPR & 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

3 Agenda Introduzione alle misure EMI Terminologia; precompliance verso full compliance Setup di misura: emissione radiate e condotte CISPR & 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

4 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 (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.

5 Precompliance Conducted Emission Testing set-up

6 Precompliance Radiated Emission Testing set-up

7 Compliance EMI receiver requirements A CISPR 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

8 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).

9 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

10 Agenda Introduzione alle misure EMI Terminologia; precompliance verso full compliance Setup di misura: emissione radiate e condotte CISPR & 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

11 Theory of Operation RF input attenuator mixer IF gain IF filter (RBW) envelope detector Input signal Pre-Selector Or Low Pass Input Filter local oscillator Log Amp video filter sweep generator Crystal Reference Oscillator Swept Spectrum Analyzer Block Diagram ADC, Display & Video Processing

12 All Digital IF Advantages RF Section ADC 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 FFT IF/BB Section on ASIC Speed: When Swept mode is slow, go FFT

13 Digital IF Improves Amplitude Accuracy Input Connector ADC DSP RF Input Attenuator 2 db Steps Pre-selector Frequency Dependent Frequency Independent Amplitude Uncertainty Ref Level Switching RBW Switching Display Scale Fidelity N9038A Receiver 0dB Analog IF (older receivers) <= +/- 1dB +/-.05dB <= +/-.5dB +/-.15dB <= +/-.85dB 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 Downconversion IF Filter IF Gain Log Amp Video Filter Log ADC

14 EMI Receiver Block Diagram ( Keysight MXE ) Input 2 Pre-amp Input 1 Transient Limiter Attenuation RF Preselector Digital IF Filter Digital Detectors FFT MXE Analog IF Filter ADC Swept vs. FFT Digital Log Amp

15 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 Narrow band signals Broadband signals

16 Wider RF Preselector Filter BW = Reduced Impulse Overload Protection Input pulse Vp Τ= pulse width RF Input Attenuator Receiver RF Section Impulse BW BW i RF Preselector Vmax = Vp Τ BW i Downconversion Max Pulse voltage into mixer is proportional to RFPS filter impulse BW (BW i ) Examples* 20 log (35MHz/9.5MHz) = 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

17 RF Preselector Bands for MXE

18 N6141A EMI Measurement Application Pre-compliance GW Instek low cost solution Compliance Keysight CXA entry-level Keysight MXE N9038A

19 CXA EMC analyzer precompliance USB LAN/USB EMSCAN Scanner

20 MXE EMI Reciever Excellent accuracy and sensitivity GHz GHz Full Cispr Compliance - -two inputs for conducted and radiated Real Time Analyzer - Up to 85 Mhz RTBW - Time Domain Scan Capability 20 Hz to 1 GHz surge protected 20 Hz to 3.5Ghz or 8.4Ghz or 26.5Ghz or 44GHz - Upgradable up to 44Ghz

21 Agenda Introduzione alle misure EMI Terminologia; precompliance verso full compliance Setup di misura: emissione radiate e condotte CISPR & 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

22 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?

23 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

24 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

25 amplitude amplitude How Time Domain Sweep Saves Time Have to dwell at each RBW Only have to dwell for each FFT BW (multiple RBWs) FFT BW Receiver Resolution BW frequency Receiver FFT BW frequency Swept or Stepped Frequency Scan Time Domain Frequency Scan

26 Window Effects and Sample Rate 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?

27 Oversampling before FFT 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

28 Time Domain improves sweep time Time Domain Scan Frequency Domain Scan CISPR Band MXE MXE 30MHz 1GHz Peak det. 10ms. dwell RBW =120kHz 3 pts/rbw ~ 12 s 242 sec smooth scan 150kHz 30 MHz Peak det 100ms. dwell RBW = 9kHz 2 pts/rbw ~ 13 s 664 sec smooth scan Page 37

29 Agenda Introduzione alle misure EMI Terminologia; precompliance verso full compliance Setup di misura: emissione radiate e condotte CISPR & 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

30 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.

31 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)

32 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

33 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

34 Real Time Operation In Real Time Operation the Analyzer s Processing (CALC) is Fast Enough to Keep Up with All Data Samples However some data may still be lost CALC Time Includes FFT or Power Spectrum, Averaging, Display Updates, etc.

35 Overlap Processing If Processing is Faster than Sampling, Perform Additional FFTs With Partially-New Time Records as Samples Come In Overlap 0% Overlap 50% Processor Idle Avoid Loss of Data Due to Windowing Window Function Accurate Amplitude Measurements of Short Duration Signals

36 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 - -

37 Snap shot FFT spectrum analyzer mixer attn filter IF A/D FFT 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)

38 Real Time Spectrum Analyzer mixer attn filter IF A/D FFT 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

39 Probability of missing signals Freq Real time BW Time Swept tuned SA Snapshot FFT SA Real time SA

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41 RTSA applications Embedded signal 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

42 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

43 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

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