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ESD Simulator Verification

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1 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 Copyright 2003 Schaffner EMC - All rights reserved
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 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 Measuring tip voltage Measured at standard test levels:
±2kV, ±4kV, ±6kV, ±8kV, ±15kV and ±25kV Measured using Electrometer or Giga-ohm meter Most standards don’t specify requirements ISO specifies 100 GOhm minimum input impedance The simulator’s 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 Tip voltage measurement using Giga-ohm meter (Brandenburg Model 139D)

6 Idealized ESD simulator waveform

7 Actual waveform measurement (Tek 7104)

8 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 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 Typical ESD current measurement system
ESD measurement system at Schaffner, Switzerland.

11 Typical ESD current measurement system (Agilent lab)
1.2m ground plane clamped to ESD table.

12 Typical ESD current measurement system

13 Performing a contact discharge into the older ESD target
Keytek MZ-15EC MiniZap Simulator.

14 Target design history IEC 801-2: 1991
No longer referenced by any current ESD standard No performance specifications Poor design - lots of ringing IEC : 1995 Referenced by virtually all current ESD standards 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 IEC 801-2 target “ball tip” Old design is no longer specified

16 IEC 61000-4-2 target Presently specified in standards
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. Example: EMCO CTC-3, and others

17 ANSI C63.16 target Proposed design
Example: Schaffner MD-102, Amplifier Research CTR-2, and others

18 Old versus new ESD targets
EMCO CTC-3 (left) Schaffner MD-102 (right).

19 New target with “driving” adapter to measure transfer characteristics
Schaffner MD-102

20 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 Waveforms of IEC 801-2 target vs. ANSI target
less HF ringing and shows true peak shape

22 Actual waveform measurement (Agilent 54855A, 1.5 GHz BW)
Old target New Target

23 Actual waveform measurement (Agilent 54855A, 6 GHz BW)
Old target New Target

24 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 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 dB Percentage % % % % %

26 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 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 Oscilloscopes - Bandwidth How does bandwidth affect observed risetime?
Let‘s assume a Gaussian rolloff

29 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 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 Oscilloscopes - Sampling rate SAE and ISO recommend 4Gs/s minimum
2 Gs/s A -16.0% 10 Gs/s A -2.9% 5 Gs/s A -3.8% 20 Gs/s A

32 Oscilloscopes – Interpolation - sin(x)/x ON or OFF?
Interpolation ON Interpolation OFF 2 Gs/s A -16.0% 2 Gs/s A -9.6% 5 Gs/s A -3.8% 5 Gs/s A -2.6%

33 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 Other factors - Do’s and don’ts
Shielding Do we need it? Position of ground cable Will it affect waveform? Orientation of simulator Automatic Measurements Must use Min and Max values to calculate 10% and 90% points Other cables Keep them well separated

35 Oscilloscope shielding - Do we need it
Oscilloscope shielding - Do we need it? Standards say yes, but probably not necessary - use distance test Scope inside Faraday cage Scope at corner of plane Scope next to simulator

36 Ground cable position Does affect results - peak, rise and duration
20 Gs/s A, 891ps Natural loop 20 Gs/s A, 926ps Loop closer to plane

37 Simulator orientation to target Does affect results - peak, rise and duration
20 Gs/s A, 891ps Simulator on axis 20 Gs/s A, 913ps Simulator tip down 10º 20 Gs/s A, 945ps Tip down 30º

38 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 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

40 Target plane size ANSI - 1. 2m x 1. 2m, IEC 1. 5m x 1
Target plane size ANSI - 1.2m x 1.2m, IEC 1.5m x 1.5m, ISO - N/A, SAE - N/A 20 Gs/s A Mini Target Plane 20 Gs/s A 1.2m2 Target Plane

41 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 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)

42 Thank you for your attention Your feedback is welcome
Greg Senko Business Manager - EMC Test Equipment Schaffner EMC (603) Ken Wyatt Sr. EMC Engr Hardware Test Mgr Agilent Technologies (719)

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