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Safety for electronic systems ESD Simulator Verification Greg Senko Business Manager - EMC Test Equipment Schaffner EMC Ken Wyatt Hardware Test Center.

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Presentation on theme: "Safety for electronic systems ESD Simulator Verification Greg Senko Business Manager - EMC Test Equipment Schaffner EMC Ken Wyatt Hardware Test Center."— Presentation transcript:

1 safety for electronic systems ESD Simulator Verification Greg Senko Business Manager - EMC Test Equipment Schaffner EMC Ken Wyatt Hardware Test Center Manager Agilent Technologies, Colorado Springs Copyright 2003 Schaffner EMC - All rights reserved Van de Graaff generator, Boston Museum of Science (photo © 2003 by Kenneth Wyatt)

2 safety for electronic systems Virtually every EMC laboratory has one or more ESD simulator. Almost none are equipped to verify the ESD simulators performance. We will cover: Verification techniques, including ISO, SAE, ANSI and IEC standards Proposed changes in the measurement setup Practical aspects of measurement setup and performance Live demonstration Copyright 2003 Schaffner EMC - All rights reserved

3 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 3 safety for electronic systems What parameters must be measured? Tip voltage Current waveform Peak Rise Current at 30ns Current at 60ns Time Constant (air discharge, auto manf) Current derivative - ANSI Draft (gives indication of smoothness) Positive peak Negative peak

4 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 4 safety for electronic systems Measuring tip voltage Measured at standard test levels: ±2kV, ±4kV, ±6kV, ±8kV, ±15kV and ±25kV Measured using Electrometer or Giga-ohm meter Most standards dont specify requirements ISO 10605 specifies 100 GOhm minimum input impedance The simulators tip voltage not affected by the measurement If a Giga-ohm meter is used, the simulator must continuously charge the high-voltage capacitor - Many older simulators provide an initial charge only, which can bleed off with time or with load

5 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 5 safety for electronic systems Tip voltage measurement using Giga-ohm meter (Brandenburg Model 139D)

6 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 6 safety for electronic systems Idealized ESD simulator waveform

7 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 7 safety for electronic systems Actual waveform measurement (Tek 7104)

8 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 8 safety for electronic systems How do we measure the current waveform? A low impedance shunt (ESD target) is used to represent a discharge into a large metallic object The shunt impedance is < 2.1 Ohms Block diagram: ATTENUATOR OSCILLOSCOPE TARGET GROUND PLANE CABLE Optional Attenuator for > 8 kV (20 dB)

9 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 9 safety for electronic systems Typical ESD current measurement system NOTE: The reason a Faraday cage was written into the original standard was that the analog phosphor storage oscilloscopes were generally susceptible to the high field energy produced by simulators. The digitizing oscilloscopes today are much more immune and the Faraday cage is no longer a must. You must confirm your measurement system is unaffected, however!

10 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 10 safety for electronic systems Typical ESD current measurement system ESD measurement system at Schaffner, Switzerland.

11 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 11 safety for electronic systems Typical ESD current measurement system (Agilent lab) 1.2m ground plane clamped to ESD table.

12 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 12 safety for electronic systems Typical ESD current measurement system

13 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 13 safety for electronic systems Performing a contact discharge into the older ESD target Keytek MZ-15EC MiniZap Simulator.

14 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 14 safety for electronic systems Target design history IEC 801-2: 1991 No longer referenced by any current ESD standard No performance specifications Poor design - lots of ringing IEC 61000-4-2: 1995 Referenced by virtually all current ESD standards No performance specifications Transfer function zero at 5-6 GHz ANSI C63.16 Draft 9 Proposed new design (uses sm resistors and tapered transitions) Flat to 6GHz Driving adapter to evaluate high frequency performance

15 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 15 safety for electronic systems IEC 801-2 target ball tip Old design is no longer specified

16 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 16 safety for electronic systems IEC 61000-4-2 target Presently specified in standards Example: EMCO CTC-3, and others The large flat disk tends to build up a pre-corona discharge, which slows the risetime and leads to variable results for air- discharge measurements.

17 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 17 safety for electronic systems ANSI C63.16 target Proposed design Example: Schaffner MD-102, Amplifier Research CTR-2, and others

18 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 18 safety for electronic systems Old versus new ESD targets EMCO CTC-3 (left) Schaffner MD-102 (right).

19 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 19 safety for electronic systems New target with driving adapter to measure transfer characteristics Schaffner MD-102

20 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 20 safety for electronic systems ANSI C63.16 target specifications Reflection coefficient of target and adapter < 0.1 Equivalent to VSWR < 1.22 Insertion loss < 0.3dB up to 4 GHz Variation of attenuation of the target -attenuator-cable chain < ±0.3dB from DC to 1GHz (< ±3.51%) < ±0.8dB from 1GHz to 4GHz (< ±9.65%)

21 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 21 safety for electronic systems Waveforms of IEC 801-2 target vs. ANSI target IEC 801-2 Target ANSI Target - less HF ringing and shows true peak shape

22 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 22 safety for electronic systems Actual waveform measurement (Agilent 54855A, 1.5 GHz BW) Old target New Target

23 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 23 safety for electronic systems Actual waveform measurement (Agilent 54855A, 6 GHz BW) Old target New Target

24 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 24 safety for electronic systems Choosing attenuators Target transfer function is ~1V/A when loaded by 50 Ohms Contact mode peak current at 8kV is ~30A Input range of most oscilloscopes is < 10V in 50 Ohm mode Therefore, an attenuator is needed to reduce the signal level 20dB is typically chosen for 10:1 ratio Contact mode to 25kV may require additional attenuation

25 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 25 safety for electronic systems Choosing attenuators Low power attenuators may damaged by the short term peak power Attenuators are available with 1kW peak power ratings Use an 18GHz attenuator with low SWR, < 1.25 to 8GHz The attenuator accuracy requires that the entire chain be calibrated Accuracy variation dBPercentage 0.11.16% 0.33.51% 0.55.93% 0.78.39% 0.910.92%

26 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 26 safety for electronic systems Choosing cables A low loss cable is required Cable length < 1m is required by most standards Double shielding is required by most standards The ANSI standard recommends RG 400 RG 214 is twice the dia, 1/2 the loss and is commonly available

27 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 27 safety for electronic systems Oscilloscopes - Bandwidth All standards require at least 1GHz bandwidth The BW/risetime of the oscilloscope is the single most limiting factor to accurately measure the pulse risetime The true risetime is related to the observed risetime as follows: The above correction is proposed in the ANSI draft standard and assumes a Gaussian rolloff in frequency response. However most digitizers use a sharper cutoff filter, 20dB/decade or higher.

28 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 28 safety for electronic systems Oscilloscopes - Bandwidth How does bandwidth affect observed risetime? Lets assume a Gaussian rolloff

29 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 29 safety for electronic systems Oscilloscopes - Sampling rate Single-shot sampling rate is the key A fast-edge triangular peak requires fast sample rate Risetime of 800 ps from 10%-90% is 80% of waveform 10 Gs/s = 100 ps/sample 8 samples in 800 ps or 10%/sample! Since peak is symmetrical and somewhat rounded actual error is < 5% (assumes a triangle shape) Effective sampling rate increased by capturing multiple shots Must have stable waveform Useful for contact mode only - never for air discharge Shot to shot variation is low for most simulators Should be used for verification - not for calibration

30 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 30 safety for electronic systems Shot-to-shot variation - 20 shots 33.3 A peak Std dev.425 ±0.64% of peak 898 ps Rise Std dev 11.9 ±0.66% of risetime

31 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 31 safety for electronic systems Oscilloscopes - Sampling rate SAE and ISO recommend 4Gs/s minimum 2 Gs/s - 27.87A -16.0% 5 Gs/s - 31.92A -3.8% 20 Gs/s - 33.18A 10 Gs/s - 32.23A -2.9%

32 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 32 safety for electronic systems Oscilloscopes – Interpolation - sin(x)/x ON or OFF? 2 Gs/s - 29.98A -9.6% 5 Gs/s - 32.32A -2.6% 2 Gs/s - 27.87A -16.0% 5 Gs/s - 31.92A -3.8% Interpolation ONInterpolation OFF

33 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 33 safety for electronic systems Calibrating the target-attenuator-scope chain It is recommended that the DC transfer function of the entire chain be measured as follows: Inject a known current Measure the resulting voltage at the oscilloscope The attenuation factor = Injected current / observed voltage Attenuation factor is used to correct waveform amplitude ATTENUATOR OSCILLOSCOPE TARGET GROUND PLANE CABLE CURRENT SOURCE Optional Attenuator for > 8 kV (20 dB)

34 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 34 safety for electronic systems Other factors - Dos and donts Shielding Do we need it? Position of ground cable Will it affect waveform? Orientation of simulator Will it affect waveform? Automatic Measurements Must use Min and Max values to calculate 10% and 90% points Other cables Keep them well separated

35 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 35 safety for electronic systems Oscilloscope shielding - Do we need it? Standards say yes, but probably not necessary - use distance test Scope inside Faraday cage Scope next to simulator Scope at corner of plane

36 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 36 safety for electronic systems Ground cable position Does affect results - peak, rise and duration Natural loop Loop closer to plane 20 Gs/s - 33.6A, 891ps 20 Gs/s - 36.9A, 926ps

37 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 37 safety for electronic systems Simulator orientation to target Does affect results - peak, rise and duration Simulator on axis Tip down 30º Simulator tip down 10º 20 Gs/s - 33.6A, 891ps 20 Gs/s - 33.6A, 913ps 20 Gs/s - 34.5A, 945ps

38 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 38 safety for electronic systems Air discharge - What risetime/peak do you want? Approach speed and environmental factors will greatly affect results - not Repeatable! Obtaining a passing waveform is a matter of patience!

39 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 39 safety for electronic systems Measurement uncertainty The estimated bounds of the deviation of a measured quantity from its true value List all the possible error sources and compute the uncertainty Uncertainty budget for each measured parameter Statement of confidence that can be placed in the value of uncertainty Does measured result truly fall within acceptable limits? National Association for Measurement and Sampling publication NIS81, The Treatment of Uncertainty in EMC Measurements Link to CE-Mag site http://www.ce-mag.com/ARG/Senko.html

40 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 40 safety for electronic systems Target plane size ANSI - 1.2m x 1.2m, IEC 1.5m x 1.5m, ISO - N/A, SAE - N/A Mini Target Plane 1.2m 2 Target Plane 20 Gs/s - 31.85A 20 Gs/s - 33.18A

41 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 41 safety for electronic systems Demonstration equipment Simulator:Schaffner NSG 435 / Keytek Minizap MZ-15EC New Target:Schaffner MD 102 (designed to new ANSI stnd) Old Target:Emco CTC-3 (designed to meet IEC 61000-4-2 stnd) Target Plane:Small sized plane for demo purposes Attenuator: Weinschel Model 2-20, 20dB, 5W, 1000W peak Cable: RG-214 1m Oscilloscope:Agilent Infiniium 54855A 6GHz BW, 20Gs/s scope ESD Monitor:Credence Technologies CTC034-3 (counts and beeps for each ESD event) www.credencetech.com www.credencetech.com

42 Copyright 2003 Schaffner EMC Inc. - All Rights Reserved 42 safety for electronic systems Thank you for your attention Your feedback is welcome Greg Senko Business Manager - EMC Test Equipment Schaffner EMC (603) 642-4694 gsenko@schaffner.com Ken Wyatt Sr. EMC Engr Hardware Test Mgr Agilent Technologies (719) 590-2852 ken_wyatt@agilent.com


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