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Near field scan immunity measurement with RF continuous wave

A. Boyer, S. Bendhia, E. Sicard

LESIA, INSA de Toulouse, 135 avenue de Rangueil, 31077 TOULOUSE cedex, France.

E-mail : alexandre.boyer@insa-toulouse.fr

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1. Introduction : immunity methods overview

2. Description of the near filed scan immunity method

3. Modeling of the aggression

4. Case studies

5. Conclusion

Outline

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Introduction : immunity methods overviewMethods Advantages DrawbacksDPI IEC 62132-3

(localized method)

Simple model

Low power, Low cost

Frequency limit 1 GHz

BCI IEC 62132-2

(localized method on N pins)

Cable injection

No specific test board

Test on actual production boards

Frequency limit : 400 MHz

Weak coupling

TEM/GTEM IEC 62132-4

(Global aggression)

High frequency method

Weak coupling

Complex coupling

Special board

Mode Stirred Chamber IEC 62132-6

(Global aggression)

High frequency method

Far field

Complex model

Much space and expensive

Objective : Find a simple method to characterize and investigate the immunity of each part of a circuit at high frequency

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Near field probe

RF generator

Field produced by the probe

Lead frame device under test

Parasitic induced currents

Principle Test bench

Description of the near field scan immunity method

• Reuse of near field scan in emission (IEC 61967-3)

• Injection of RF disturbances by a miniature near field probe

Advantages :

Few mm

Magnetic probe

Localized disturbances coupled on lead frame of packages

Produce immunity cartography or scan

No specific test board or test fixture required

Frequency limitation : several GHz, linked with the resonances of the antenna

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Description of the near field scan immunity methodGeneral set-up of near field aggression experiment

• Generation of continuous wave aggression.

• The use of a directional coupler allows to know the forward power in the injection loop. Results are given in terms of forward power.

• For each frequency, the forward power is increased until the failure is detected

• The forward power that creates a failure is stored.

• The probe is then moved to a new position

Signal synthesizerAmplifier

Near fieldprobe

Device under test

OscilloscopeFailure detection :

Pattern exit

Pforw

Directional coupler

Prefl

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Modeling of the aggressionElectrical modeling of the probe

Hi

Tangential magnetic field probe

• Validation of the model up to 10 GHz

• No antenna resonance below 10 GHz

n

dS

Ground plane

I1

L1

L2

RF Generator

Electrical modeling of the coupling

Inductive coupling

10

1

212 2 I

SdH

IM S

i

I

21

12

LL

Mk

• Interesting method to evaluate the mutual coupling coefficient : PEEC method

L=0.13m, εr=2.2Line with losses

Inductive load

SPICE model for the magnetic probe

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Modeling of the aggressionPartial Element Equivalent Circuit to find mutual coupling

Conductor A Conductor B

IaIb

Inductive coupling L ab

1. All conductors are meshed in elementary filaments

2. Inductive coupling between conductors is computed by adding the influence of all filaments on each other :

ABA B

ba

ba

ba

abdVdV

rr

ll

SSL

4

0

3. Gives directly an electrical model which can be simulated under SPICE.

La

Lb

Lab

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Coupling vs. position

• Good correlation for maximum coupling

Coupled power vs. probe position

Electrical modeling of the coupling: Validation

Validation case : coupling to a micro-strip line

Modeling of the aggression

50Ω

εr=2.2

xy

z

h=1mm

40dB Amplification

Signal synthetizer

Pmeasured

(dBmW)Spectrum analyzer

Scan on X

+20dB/dec.

Transmission coef. vs. frequency

• Efficient coupling at high frequency

• Model valid until 6 GHz

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Modeling of the radiated magnetic field

r

b

x

y

z

rH

H

E

I

r

b

x

y

z

rH

H

E

Elementary loop

rj

oooo

o

rj

ooo

o

r

o

o

er

jrr

jbIjH

er

jr

bIjH

3322

2

2

33

2

2

111sin

4

11cos

4

2

Modeling of the aggression

Based on the approximation of the elementary loop crossed by a current

Comparison with measurement – Calibration of the injection loop

Calibration of the injection loop to determine the radiated field as a function of the incident power, the frequency and the distance.

h=1mm

RF Generator

Spectrum analyzer

Measurement probe(calibrated)

Injection probe

xy

z

Good correlation until 2GHz

Hy(f) for h=1mm

Hy(x) for h=1mm and f=500MHz

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Development of a tool under IC-EMC :

• Compute coupling between a magnetic probe and the package leads

• Build a SPICE-compatible electrical model of the aggression

• Compute H field

Modeling of the aggression

IC-EMC

Immunity simulation flow :

Ibis file

Package geometry

DUT SPICE model

SPICEnetlist of DUT+aggression

Probe dimensions

H field computation

IC-EMC

Fo Po

SPICE

Immunity criteria

checked ?

no

Extract forward power

yes

Transient simulation

Results

freq

Pinjected

fo

Po

freq

Pinjected

fo

Po

Susceptibility threshold

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Aggression of the PLL of a 16 bit microcontroller

Case studies

Hy

Scanned area• Tangential H field

• Frequency 490 MHz

• Scan height 0.25 mm

• Criteria : 5% variation of the frequency of the bus clock

Immunity cartography

Apparition of a weakness zone located on the digital supply of the PLL pin (VddPLL)

VddPLL aggression vs. frequency

Quartz susceptibility

450 MHz

Impedance between VddPLL and

Vss core

Correlation between immunity threshold and impedance between VddPLL and ground of core Vss450 MHz

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Case studiesAggression of the PLL of a 16 bit microcontrollerA measurement in a TEM cell has been tried : no failures detected.

H field generated close to the probe above a pin of a TQFP 144 package:

Theoretical H field generated in TEM cell :

mAE

HmVd

VE

VPVthenondBmPif

TEM

TEM

TEM

in

TEM

incininc

/47.0/176045.0

9.7

9.7505031

For an equivalent power, the maximum H field generated by the probe is 20 times greater than in TEM cell.

H=1mm

Pforw = 31dBm

F=480MHz

Hmax=9A/mHmean=3.6A/m

Htot (A/m)

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Aggression of a 10 bit ADC of a 16 bit microcontroller

Case studies

Hy

Scanned area

VSSA

AN0

• Tangential H field

• Frequency 500 MHz

• Scan height 0.25 mm

• Criteria : LSB modification

Highlights 2 susceptible areas located on the analog ground of the ADC pin (VSSA) and on the input of the ADC channel (AN0).

AN0 aggression vs. frequency

Aggression of the input of the ADC

In-band aggression

VSSA influence

High frequency susceptibility

Weakness at low frequency (in-band aggression) which depends on conversion clock

Weakness at high frequency (800MHz-1.4GHz)

Second weakness linked with VSSA susceptibility (see next slide)

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Case studiesAggression of a 10 bit ADC of a 16 bit microcontroller

VSSA aggression vs. frequency

Aggression of the analog ground of the ADC

• Correlation between immunity threshold and impedance between VSSA and supply rails of core Vdd/Vss.

• These weaknesses are linked with supply impedance resonances

Impedance between VSSA and Vdd/Vss core

In-band aggression

Weakness at low frequency (in-band aggression)

Weakness around 500MHz

500 MHz

450 MHz

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Case studiesAggression of an input port of a 16 bit microcontroller

Near field aggression of an input portDPI aggression of an input port

• Two different injection methods, two different results.

• Only one common point : susceptibility level decreases with frequency above 1 GHz.

• Does the same model predicts these 2 results ? Currently, only DPI injection modeling has been established. Near field injection is on going.

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Case studiesAggression of an input port of a 16 bit microcontroller

Susceptibility SPICE model

• Model of DPI injection valid up to 1.8 GHz

• Z model shows the influence of the different parameters

Injection path model

measure

Block behavior model

Measure/given

IBIS modelMeasure/given

Passive Distribution Network

Measure/ICEM

Reuse of the ICEM model built for emission. Useful blocks to build a susceptibility model in DPI :

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Case studiesAggression of an input port of a 16 bit microcontroller

Comparison DPI injection measurement/simulation

Comparison measure/simulation of forward power

Comparison measure/simulation of transmitted power

• Good correlation until 900 MHz.

• Model built from first order parameters, without any confidential data

• High influence of the injection path and of the PDN and IO model. Essential parameters for a future ICIM model.

Simulation problem

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Conclusion

• A method of susceptibility characterization of ICs using near field has been presented.

• Main advantages :

Valid until 6 GHz

Help to detect susceptible pins of the integrated circuits

Simple inductive model

• A modeling software have been developed to predict the coupling, the radiated field and build an electrical model for susceptibility.

• Several cases have been presented which shows different effects of near field aggression.

• Future work : propose this method as an extension of BCI standard method to higher frequencies