Transcript Document

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]
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Outline
1. Introduction : immunity methods overview
2. Description of the near filed scan immunity method
3. Modeling of the aggression
4. Case studies
5. Conclusion
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Introduction : immunity methods overview
Methods
Advantages
DPI IEC 62132-3
(localized method)
Simple model
Frequency limit 1 GHz
Low power, Low cost
BCI IEC 62132-2
(localized method on
N pins)
Cable injection
Frequency limit : 400 MHz
No specific test board Weak coupling
Test on actual
production boards
TEM/GTEM IEC
High frequency
method
Weak coupling
Complex coupling
Special board
High frequency
method
Far field
Complex model
Much space and expensive
62132-4
Drawbacks
(Global aggression)
Mode Stirred
Chamber IEC 62132-6
(Global aggression)
Objective : Find a simple method to characterize and investigate
the immunity of each part of a circuit at high frequency
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Description of the near field scan immunity method
• Reuse of near field scan in emission (IEC 61967-3)
Few mm
• Injection of RF disturbances by a miniature near field probe
Magnetic probe
RF generator
Near field
probe
Field produced
by the probe
Lead frame
device under test
Parasitic induced
currents
Test bench
Principle
Advantages :
 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 method
General set-up of near field aggression experiment
Signal synthesizer
Amplifier
Pforw
Prefl
Directional coupler
Failure detection :
Near field
probe
Oscilloscope
Device under test
Pattern exit
• 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
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Modeling of the aggression
Electrical modeling of the probe
Tangential magnetic field probe
L=0.13m, εr=2.2
Line with losses
Inductive load
SPICE model for the magnetic probe
• Validation of the model up to 10 GHz
• No antenna resonance below 10 GHz


  H i  dS
2
S
M 12 
I 0 
I1
I1
Electrical modeling of the coupling

2
RF Generator
L1
I1
n
dS
Ground plane
Hi
k
L2
Inductive
coupling
M 12
L1  L2
• Interesting method to evaluate the mutual
coupling coefficient : PEEC method
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Modeling of the aggression
Partial Element Equivalent Circuit to find mutual coupling
Ib
Ia
Conductor A
2.
1. All conductors are meshed
in elementary filaments
Conductor B
Inductive coupling between conductors is computed by adding the influence
of all filaments on each other :
0
la  lb
Lab 
dVB dVA

4  S a Sb A B ra  rb
3.
Gives directly an electrical model which
can be simulated under SPICE.
La
Lab
Lb
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Modeling of the aggression
Electrical modeling of the coupling: Validation
Signal
synthetizer
Validation case : coupling
to a micro-strip line
40dB
Amplification
Scan on X
z
εr=2.2
h=1mm
y
x
50Ω
Spectrum
analyzer
Pmeasured
(dBmW)
+20dB/dec.
Coupling vs. position
Coupled power vs. probe position
Transmission coef. vs. frequency
• Efficient coupling at high frequency
• Good correlation for maximum coupling
• Model valid until 6 GHz
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Modeling of the aggression
Modeling of the radiated magnetic field
z
q
 1
2 o2
1 
Hr  j
Ib 2 cosq 
 j 3 3 e  j r
4o
o r 
 or
o

Hq
r
b
I

Hr

Ej
Based on the approximation of
the elementary loop crossed by a
current
 1
 o2
1
1 
Hq  j
Ib 2 sin q  j
 2 2  j 3 3 e  j r
4o
o r 
 or o r
o
y
Elementary loop
x
Comparison with measurement – Calibration of the injection loop
RF Generator
Injection probe
z
h=1mm
x
y
Hy(f) for h=1mm
Measurement probe
(calibrated)
Spectrum
analyzer
Hy(x) for h=1mm and
f=500MHz
Calibration of the injection loop to
determine the radiated field as a
function of the incident power, the
frequency and the distance.
Good correlation
until 2GHz
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Modeling of the aggression
Development of a tool under IC-EMC :
• Compute coupling between a magnetic probe and the package leads
IC-EMC
• Build a SPICE-compatible electrical model of the aggression
• Compute H field
Immunity simulation flow :
Fo
no
Po
Probe
dimensions
SPICE netlist of
DUT+aggression
Ibis file
Package
geometry
H field
computation
Transient SPICE
simulation Immunity criteria
checked ?
DUT SPICE
model
yes
Pinject
ed
Extract forward
power
Results
Po
IC-EMC
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fo freq
Susceptibility threshold
Case studies
Aggression of the PLL of a 16 bit microcontroller
Scanned area
• Tangential H field
• Frequency 490 MHz
• Scan height 0.25 mm
• Criteria : 5% variation of the frequency of
the bus clock
Hy
Immunity cartography
Apparition of a weakness zone located on
the digital supply of the PLL pin (VddPLL)
Quartz
susceptibility
450 MHz
VddPLL aggression vs. frequency
450 MHz
Correlation between
immunity threshold and
impedance between
VddPLL and ground of
core Vss
Impedance between VddPLL and
Vss core
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Case studies
Aggression of the PLL of a 16 bit microcontroller
A 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:
Htot (A/m)
Pforw = 31dBm
F=480MHz
H=1mm
Hmax=9A/m
Hmean=3.6A/m
 Theoretical H field generated in TEM cell :
if Pinc  31dBm on 50 then Vin  Pinc  50  7.9V
ETEM 
Vin
7.9
E

 176 V / m  H TEM  TEM  0.47 A / m
dTEM 0.045

For an equivalent power, the maximum H field generated by the probe is 20 times
greater than in TEM cell.
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Case studies
Aggression of a 10 bit ADC of a 16 bit microcontroller
Scanned area
• Tangential H field
VSSA
• Frequency 500 MHz
• Scan height 0.25 mm
AN0
Hy
• 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).
VSSA
influence
Aggression of the input of the ADC
 Weakness at low frequency (in-band aggression)
which depends on conversion clock
In-band
aggression
 Second weakness linked with VSSA
susceptibility (see next slide)
High frequency
susceptibility  Weakness at high frequency (800MHz-1.4GHz)
AN0 aggression vs. frequency
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Case studies
Aggression of a 10 bit ADC of a 16 bit microcontroller
Aggression of the analog ground of the ADC
 Weakness at low frequency (in-band
aggression)
In-band
aggression
 Weakness around 500MHz
500 MHz
VSSA aggression vs. frequency
• Correlation between immunity threshold and
impedance between VSSA and supply rails of core
Vdd/Vss.
450 MHz
• These weaknesses are linked with supply
impedance resonances
Impedance between VSSA and
Vdd/Vss core
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Case studies
Aggression of an input port of a 16 bit microcontroller
DPI aggression of an input port
Near field 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 studies
Aggression of an input port of a 16 bit microcontroller
Reuse of the ICEM model built for emission. Useful blocks to
build a susceptibility model in DPI :
Block behavior
model
Injection
path model
measure
Measure/given
Susceptibility
SPICE model
Passive Distribution
Network
IBIS model
Measure/ICEM
Measure/given
• Model of DPI injection
valid up to 1.8 GHz
• Z model shows the
influence of the different
parameters
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Case studies
Aggression of an input port of a 16 bit microcontroller
Comparison DPI injection measurement/simulation
Simulation
problem
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.
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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
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