Safety for electronic systems ESD Simulator Verification Greg Senko Business Manager - EMC Test...

safety for electronic systems

ESD Simulator Verification

Greg SenkoBusiness Manager - EMC Test EquipmentSchaffner EMC

Ken WyattHardware Test Center ManagerAgilent Technologies, Colorado Springs

Copyright 2003 Schaffner EMC - All rights reserved

Van de Graaff generator, Boston Museum of Science (photo © 2003 by Kenneth Wyatt)


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

Copyright 2003 Schaffner EMC Inc. - 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 10605 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 chargethe 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 adischarge into a large metallic object

The shunt impedance is < 2.1 Ohms

Block diagram:

ATTENUATOR 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 waswritten into the original standardwas that the analog phosphorstorage oscilloscopes were generallysusceptible to the high field energyproduced by simulators.

The digitizing oscilloscopes todayare much more immune and theFaraday cage is no longer a must. Youmust confirm your measurement systemis unaffected, however!


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ESD measurement systemat Schaffner, Switzerland.


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Typical ESD current measurement system(Agilent lab)

1.2m ground plane clampedto ESD table.


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13


Performing a contact discharge into the older ESD target

Keytek MZ-15EC MiniZapSimulator.


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 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


IEC 801-2 target “ball tip”

Old design is no longer specified


16


IEC 61000-4-2 target

Presently specified in standards

Example: EMCO CTC-3,and others

The large flat disk tendsto build up a pre-coronadischarge, which slowsthe risetime and leads tovariable results for air-discharge measurements.


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).


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New target with “driving” adapter to measure transfer characteristics

Schaffner MD-102


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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

IEC 801-2Target

ANSI Target -less HF ringingand shows truepeak 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 Percentage0.1 1.16%0.3 3.51%0.5 5.93%0.7 8.39%0.9 10.92%


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.

2_

2_ chaintmeasuremenobservedpulseesd risetimerisetimerisetime


28


Oscilloscopes - Bandwidth

How does bandwidth affect observed risetime?

Let‘s assume a Gaussian rolloff

Pulse Risetime

(ps)

Scope BW (GHz)

Scope Risetime

(ps)

Observed Risetime

(ps) Difference % Error

700 1 350 783 82.62379 11.8%

700 1.5 233 738 37.86479 5.4%

700 2 175 722 21.54348 3.1%

700 3 117 710 9.655629 1.4%

700 4 88 705 5.447553 0.8%

700 6 58 702 2.42635 0.3%


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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


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Shot-to-shot variation - 20 shots

33.3 A peakStd dev .425 ±0.64% ofpeak

898 ps RiseStd dev 11.9 ±0.66% ofrisetime


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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


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 ON Interpolation OFF


33


Calibrating the target-attenuator-scope chain

It is recommended that the DC transfer function of the entire chainbe 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 ATTENUATOR OSCILLOSCOPE

TARGET

GROUND PLANE

CABLECURRENT 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

• 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


Oscilloscope shielding - Do we need it?

Standards say yes, but probably not necessary - use distance test

Scope insideFaraday cage

Scopenext tosimulator

Scopeat cornerof plane


36


Ground cable position

Does affect results - peak, rise and duration

Natural loop

Loop closerto plane

20 Gs/s - 33.6A,891ps

20 Gs/s - 36.9A,926ps


37


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


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Air discharge - What risetime/peak do you want?

Approach speedand environmentalfactors will greatlyaffect results - notRepeatable!

Obtaining a passingwaveform is amatter 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

http://www.ce-mag.com/ARG/Senko.html


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Target plane size

ANSI - 1.2m x 1.2m, IEC 1.5m x 1.5m, ISO - N/A, SAE - N/A

Mini TargetPlane

1.2m2

Target Plane

20 Gs/s - 31.85A

20 Gs/s - 33.18A


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 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 andbeeps for each ESD event) www.credencetech.com


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Thank you for your attention

Your feedback is welcome

Greg SenkoBusiness Manager - EMC Test EquipmentSchaffner EMC

(603) [email protected]

Ken WyattSr. EMC EngrHardware Test MgrAgilent Technologies

(719) [email protected]

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