Improve EMC Compliance Testing Throughput with Time Domain Scanning. Daniel Bockstal Keysight Technologies Belgium

Transcription

1 Improve EMC Compliance Testing Throughput with Time Domain Scanning Daniel Bockstal Keysight Technologies Belgium

2 Agenda Introduction/Overview What Is Time Domain Scanning Benefits of Time Domain Scanning - Commercial - MIL STD Issues/Concerns Using appropriate Dwell Time Complying with CISPR standards Preselector design 2

3 Efficient EMC Testing Improves Revenue Benefits both Compliance Test Houses and Manufacturers Compliance testing Chamber time is limited resource Reducing test time improves efficiency and profitability Precompliance testing Rapid diagnosis of early designs speeds time-to market, facilitating product sales 3

4 Factors Affecting EMC Test Times Many factors affect both Compliance and Precompliance Test times: Device Under Test (DUT) setup time Receiver/ Spectrum Analyzer Scan times Turntable and Antenna movement times Suspect frequency analysis Final Measurement Report Generation Customizable in 6/21/2016 Footer 4

5 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 5 5

6 Key Benefit: Reduced Test Time! Collect list of suspect frequencies faster Device Under Test DUT Emissions 6 Benefits CISPR/FCC testing the most Commercial testing requires turntable and antenna optimization = more required scanning 6

7 How Time Domain Sweep Saves Time Have to dwell at each RBW Receiver Resolution BW Only have to dwell for each FFT BW (multiple RBWs) Receiver FFT BW (Acquisition BW) amplitude amplitude frequency Swept or Stepped Frequency Scan Time Domain Frequency Scan frequency 7 7

8 How Time Domain Sweep Saves Time Uses High overlap FFT to collect emission data simultaneously over a frequency span that includes multiple resolutions bandwidths As opposed to frequency domain where data is collected (and dwelled) in individual resolution, bandwiths TDS saves time because the dwell time is applied once for the given FFT bandwidth. Receiver collects data in a wider bandwidth and processes it into the appropriate regulatory bandwidth

9 How is it done

10 How is it done High degree of overlap in time domain ensures that impulsive signals are captured and measured accurately

11 Time Domain Scan is Not Real Time Spectrum Analysis Time Domain Scan FFT technology to speed frequency scanning High overlap to ensure capture and accuracy Provides CISPR-required amplitude accuracy Accepted by CISPR for Compliance meas. Real Time Spectrum Analysis FFT technology to enhance signal analysis Very wide bandwidth signal capture Provides unique insights into high-speed signals Very focused diagnostic tool No direct application to EMC Compliance 11

12 What about Real Time Spectrum Analysis? Real Time is a Diagnostic tool only - not required by any Compliance standard - no clear value to Compliance Measurement Useful in very specific diagnostic applications - e.g., very fast intermittent signals - not needed for the majority of typical EMI problems (e.g., shielding issues, cross-talk, high signal levels) 12 Agilent Confidential

13 Time Domain acceptance Time domain scanning accepted by CISPR. Many (but not all) CISPR product standards allow it now. The others are in the process of beein changed. 13

14 Review: CISPR Radiated Measurement Methodology 1. Fast Prescan to collect all suspect emissions i. Scan speed limited by CISPR ii. Speed limit ensures you capture all emissions iii. Typically use Peak detector, but can use CISPR detector TDS Helps Here 2. Identify all emissions above target limit line 3. Perform final measurement on individual signals i. Find peak of signal, then make final measurement using appropriate CISPR detector: Quasi-Peak, EMI-Avg, RMS-Avg ii. Requires that weighted amplitude of each final signal be monitored to ensure that it s steady. If not steady variation should be measured for 15 sec. If too much variation should be monitored for a longer time (excessive dwell time negates time saving of TDS). As per CISPR :2010 ed. 3.1 section

15 Test Time Reduction Example: CISPR*-based Test DUT 1 to 4 m above ground plane Test in vertical and horizontal position MXE EMI Receiver 360 deg 3 or 10 m 1. rotate DUT through 360, scanning every 15 = 24 scans 2. test at 3 antenna heights (from 1 4 meters) x 3 3. both vertical and horizontal orientation x 2 Purpose: identify peak emissions 144 scans collect a list of suspect emissions for final measurement * Example based on methodology defined in CISPR : Edition 3.1 section

16 Long Dwell Time Plus Many Scans = Lots of Time DUT 1 to 4 m above ground plane Test in vertical and horizontal position MXE EMI Receiver 360 deg 3 or 10 m 16 Frequency Domain Scan CISPR Band 30MHz 1GHz Peak det. 10ms. dwell RBW =120kHz 3 pts/rbw 150kHz 30 MHz Peak det 100ms. dwell RBW = 9kHz 2 pts/rbw Typical Industry Swept or Stepped times ~ 250 sec sec x 144 scans 250 sec/scan 10 hours Not counting antenna and turntable positioning time 16 Agilent Confidential

17 Time Domain Improves Sweep Time Time Domain Scan Frequency Domain Scan CISPR Band 30MHz 1GHz Peak det. 10ms. dwell RBW =120kHz 3 pts/rbw Typical Industry TDS times Typical Industry Scan times ~.5 to 13 seconds ~ 250 seconds 150kHz 30 MHz Peak det 100ms. dwell RBW = 9kHz 2 pts/rbw ~.1 to 11 seconds seconds Agilent Confidential

18 Time Domain Scan Offers Significant Pre-scan Time Reduction DUT 1 to 4 m above ground plane Test in vertical and horizontal position MXE EMI Receiver 360 deg 3 or 10 m 18 CISPR Band 30MHz 1GHz Peak det. 10ms. dwell RBW =120kHz 4pts/RBW 150kHz 30 MHz Peak det 100ms. dwell RBW = 9kHz 4 pts/rbw Time Domain Scan Typical Industry TDS Time ~.5 to 13 seconds ~.1 to 11 seconds 144 scans 2 x ~250 sec/scan 10 hours 4.8 minutes Not counting antenna and turntable positioning time 18 Agilent Confidential

19 TDS Benefit for Testing Short Operation-Time Devices Example: Automotive Starter motors Operating for extended periods during testing leads to overheating / thermal damage Time domain scanning significantly reduces test time. 19

20 Agenda Introduction/Overview What Is Time Domain Scanning Benefits of Time Domain Scanning - Commercial - MIL STD Issues/Concerns Using appropriate Dwell Time Complying with CISPR standards Preselector design

21 TDS Dwell Time Must be as Long or Longer than the Emission Pulse Period TDS Dwell Time = 20ms Correct Dwell Time Emission 2usec RF pulse Pulse Period 20ms TDS Dwell Time = 10ms time TDS misses pulse, signal not displayed Incorrect Dwell Time Emission 2usec RF pulse time Pulse Period 20ms Customizable in 6/21/2016 Footer 21

22 Compliance with CISPR Time Domain accepted in the Receiver as of CISPR : Usable for pre-scan to create suspect list? Yes this is the key contribution 2. Usable for Final measurement? a) only if standard references CISPR : currently, only CISPR 13 and CISPR 32 - other CISPR documents being adapted 22

23 Compliance with CISPR (continued) 2. Usable for Final measurement? b) methodology must comply with recommended measurement methodologies CISPR : must monitor each suspect to ensure QP value is constant - if QP not constant, must monitor for 15 seconds - if QP varies by more than +/- 2dB in 15 seconds, signal needs to be monitored for a longer period. Single TDS sweep does not meet CISPR requirements for Final Measurement 6/21/

24 Preselector Design Considerations Speed vs Susceptibility to Overload TDS speed is a function of: - width of IF acquisition bandwidth - processing speed Acquisition bandwidth limited by RF Preselection bandwidth 6/21/

25 Preselection What is it, Why use it? Input Low band Path ( 3.6 GHz in X-series) RF Low Preselector pass (bandpass filter filters) Low band Down-conversion Simplified Spectrum EMI Analyzer Receiver RF Input Attenuator Front End High band Path RF Preselector YIG preselector filter (microwave bands) ~ 60 MHz 3dB BW Microwave band Down-conversion Bank of Filters before first mixer (fixed or tuned) critical piece of a CISPR-compliant EMI receiver Helpful when measuring large impulses (which have wideband spectral energy) reduces broadband energy to 1 st Mixer measure with less input attenuation Provides Dynamic Range to measure CISPR pulse / meet CISPR 16 requirements 25

26 Wider Preselector Filters Enable Faster Scanning Speed Input freq Preselector Down- Convert Acquisition BW A/D Display Micro Processor Narrow Preselector Filters Acq. BW Wide Preselector Filter Acquisition BW freq. Wider Preselector Filters enable freq. Use of Wider Acquisition BWs Fewer Acquisitions for a given frequency range Faster Scanning..BUT there is a Problem. 26

27 Wider Preselector Filters = Reduced Impulse Overload Protection Input pulse Vp Receiver RF Section Impulse BW BW i Vmax = Vp Τ BW i Τ= pulse width RF Input Attenuator RF Preselector Downconversion Max Mixer input voltage is proportional to Preselector Filter Bandwidth Receiver with Wider Preselector filters will Overload earlier for same pulse acquisition bandwidth 27 Agilent Confidential 27

28 Compare Two Receivers: Wider Filters Overload First Input pulse Vp Τ= pulse width Receiver 1: Wide Preselector Filters RF Input Attenuator Wide BW RF Preselector Receiver 2: Narrow Preselector Filters RF Input Attenuator Narrow BW RF Preselector Vp1 Vp2 Downconversion Downconversion Vp1 Overloads Receiver 1 Vp2 < Vp1 Vp2 does not overload Receiver 2 Wider Preselector filters result in lower impulse dynamic range 28 Agilent Confidential 28

29 Compare Two Receivers: Wider Filters Require More Input Attenuation to Eliminate Overload Input pulse Vp Receiver 1: Wide Preselector Filters Att1 RF Input Attenuator Wide BW RF Preselector Vp1 Receiver 2: Narrow Preselector Filters Rx 1 requires larger Att1 to eliminate overload! Att1> Att2 Τ= pulse width Att2 RF Input Attenuator Narrow BW RF Preselector Downconversion Downconversion Wider Preselector filters can result in worse sensitivity Rx1 sensitivity now worse than Rx2 29 Agilent Confidential Vp2 29

30 Summary Time Domain significantly reduces test time! -CISPR - Accepted by CISPR for use in receivers - Greatest value is in Prescan - MIL STD 461F Not specifically called out in 461F Being considered for mention in 461G Critical to use appropriate dwell time - Dwell time must be at least 1/ (DUT Pulse repetition rate) - needed to ensure emission during Dwell period Be aware of lower overload thresholds when using receivers with wide preselector filters 30

31 Time Domain Demo 31