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1/18
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 : [email protected]
2/18
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
3/18
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
4/18
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
5/18
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
6/18
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
7/18
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
8/18
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
9/18
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
10/18
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
11/18
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
12/18
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)
13/18
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)
14/18
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
15/18
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.
16/18
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 :
17/18
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
18/18
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