alexander gerfer & michael eckert...alexander gerfer & michael eckert fr-pm-3 capacitor fr-pm-3...
TRANSCRIPT
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FR-PM-3
Practical EMI Filter Design
Workshop IEEE 2008 Detroit
Alexander Gerfer & Michael Eckert
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Capacitor
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Capacitor : Equivalent Circuit
Inductance of connection:SMD-types 1 nH ... 5 nHwired 10 nH ... 50 nH !
ESR:SMD-types 20 mΩ ... 300 mΩ
up to 1 Ω(see Datasheet )
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Impedance vs. Frequency of Capacitors
978-1-4244-1699-8/08/$25.00 ©2008 IEEE
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Simulation Datas for Caps from KEMET Spice
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Simulation Datas for Caps from KEMET Spice
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Capacitance: DC-Bias and Temperature
Capacitance decrease by DC-bias !!!
Effective only 8.6 µF !!
Capacitance decrease temperature increase (@ = 0VDC 18 µF !!)
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Capacitor : KEMET Spice Simulation Model
C0805C104K3RAC @ 25°C, 0VDC, 41,687 kHz LTspicewww.kemet.com www.linear.com
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Pratice-Tip: SRF of SMD-Capacitors
Example 1:Filter with maximum attentuation at f = 500 MHz in a system ZA = ZB = 100 Ω = konst.;T-Filter Step 1:
choose C with SRF @ 500 MHz
=> Nomogramm:
size 1206 ; C = 68 pF
68 pF
Step 2:calculation of Ls
SRF = 500 MHz :
nHCL resSS49,11 2 =⋅= ω
Capacitance [pF]
SRF
[
MHz
]
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What is an Inductor ?
„Headache-Parts“ ?! A mystery.........
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What is an Inductor ?
technical view:a piece of wire wounded on something
a filter
an energy-storage-part (short-time)
examples:
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What is an EMC-Ferrite ?
technical view:Absorber for RF
frequency dependent filter
examples:
EMC Snap-Ferrites EMC-Ferrites forFlatwire
SMD-FerriteWE-CBF
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Current
Magnetic field H wire
The basics of Inductive ComponentsMagnetic Field; example: long, straight wire
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The basics of Inductive ComponentsMagnetic Field; toroidal & rod core
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Magnetic field strength H of some configurations
RIH⋅⋅
=π2
RINH⋅⋅
⋅=π2
lINH ⋅=
long, straight wire
Toroidal Coil
Long solenoid
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Magnetic field H in the air and in a ferrite core
Air Ferrite core
I2xπxRaverage
H1=H2=H= But : B1=B2
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Permeability ?
Permeability (µr):describes the ability to concentrate the magnetic flux in the core material
Typical Permeability µr :
Iron Powder Cores / Superflux : 50 ~ 150
Nickel-Zink : 40 ~ 1500
Mangan-Zink : 300 ~ 20000
HB r ⋅⋅= µµ0
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Permeability µr
HB r ⋅⋅= µµ0HB ⋅= 0µInduction in air:
Linear Function !
Induction in Ferrite:
Non-Linear Function ( µr !)
The relative Permeability is dependent on Field Strength H; Temperature and a frequency-dependent parameter....
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Saturation effect
saturated
not saturated
H~I
B~
I
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Permeabilität vs. Temperatur
0
200
400
600
800
1000
1200
1400
-50 23 50 85 125 150 160 250
Temp. (°C)
µr
Permeability vs. temperature
620- 40%
+ 40%Curie-Temperature
(µr = 1 )
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How to find the best part for my application ?
The key to success is understanding of :Core Material Comparison
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Core Material Properties Measurement
core material
Impedance Analyser core material parameter
XRZ L22 +=
X LR (f)
XL(NiZn)
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Core Material Parameters of Ferrites
ωL
R(f)
Impedance of Coil with core
material
( )jLjZ =−= |||0 µµω
Impedance of same coil but w/o
core material ! core material
ωL0
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Complex Permeability
||0 µω LR =
|0 µω LjX L =
frequency dependentcore losses
frequency dependentinductive portion
L0 inductance without core
( ) jXRjLjZj
+=−=
−=|||
0
|||
µµω
µµµ
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Comparison of core materials: Inductive behaviour
=> It depends on application frequency for EACH Core-Material !FR-PM-3
Comparison of core materials: Losses
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When to use an Inductor ?When to use an EMC-Ferrite ?
- Application: Storage ChokeRequest: lowest possible core losses
at application frequency
- Application: signal-filter in RF-stages:
Request: low losses => high Q in frequency band
- Application: EMI absorber-filter
Request: high core losses
at noise frequency range
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Equivalent circuit : Inductor /Ferrite
Parasitic Capacitance:SMD-EMC-Ferrite 5 fF ... 5 pFwinded Inductors 10 pF ... 500 pF !
Losses:Inductors (at SRF ! ) up to 30 kΩSMD-EMC-Ferrite (broadband !) 10 Ω ... 3 kΩ
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SMD-Ferrite listed in LTspice
Freeware !Download at www.linear.com_FR-PM-3
Normal Type SMD-Ferrites in LTspice
You can sort database by :Part.Nr.; DCR; Current ; Impedance @100MHz ormaximum Impedance @ desired frequency
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Simulation-Modell for EMC-Ferrites
Model as Parallel-Circuit withconstant Parametern for Rp / Lp / Cp
can be used in anySimulationprogram (like P-SPICE or Electronics Workbench, ...) !
Datas: see Book „Trilogy of Inductors“Seite 113ff
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SMD-Ferrites Models in LTspice
Z[I]All High Current Chip Beads (> 1A)
are modeled in their Current Dependend Impedance behaviour
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SMD-Ferrites Models in LTspice
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SMD-Ferrites Models in LTspice: Impedance vs. DC-bias
P/N: 74279252
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Inductors listed in LTspice
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Structured interference suppression
• Recognise the coupling mode:• common mode noise• differential mode noise
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Structured interference suppression
• Procedure to find out– Use split ferrite
• common mode noise⇒ noise reduction / stable noise immunity
• differential mode noise=> no difference to see
1. Basics
2. Coupling mode
3. Filter topologies
4. Measuring
5. Simulation tools
6. Layout recommend.
7. Application
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How can we find out what interference we have on the PCB‘s?
Take a Snap Ferrite and fix it on the cable(both lines e.g. VCC and GND)
if noise is reduced ornoise immuntiy increase
you have Common Mode Interference
if not
you have Differential Mode Interference
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Ferrite as Common-Mode Filter
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Increase impedance with more turns
incr
ease
Impe
danc
e
Fres.-decrease
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Why current compensation?
N1
N2
Power line Noise
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Filtering with two Inductors
Signal before Filter: Signal after Filter:The Filter is effective on both: Differential & Common Mode Currents !
signal rise-time affected !not usefull for high-speed signals
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Filtering with common mode chokes
Signal before Filter Signal after FilterThe Filter is only active for Common Mode Noise !
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sectional winding bifilar winding
< advantage? >
Why bifilar / sectional winding ?
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For example: WE-SL2 744227SCommon Mode suppression
Differential Mode suppressionis high!
Sectional winding:
ATTENTION:SECTIONELL WINDING MUST BEUSED ON MAINS-POWER SUPPLY !
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Bifilar winding:
For example: WE-SL2 744227Common Mode suppression
Differential Mode suppressionis low!
Differential Mode S-Type
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Common Mode Choke
noise (Common Mode )
Data signal (Differential)
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Filtering with Common Mode Choke: USB
example: USB 2.0 Datenline Filter
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USB 2.0 Filtering with WE-CNSW CMC
Measuring Point TP2
EMI-part EMI-part
90 Ohm @ 100 MHz C.M. 600 Ohm @ 100 MHz C.M. WE-CBF 20 Ohm @ 240 MHz D.M. 40 Ohm @ 240 MHz D.M. 120 Ohm @ 100 MHz
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Common Mode Choke Model in LTspice
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Common Mode Choke Model in LTspice
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Common Mode Choke Model in LTspice
P/N: 744212100
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EMI-Filter topologies, Simulation and Layout tips
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Find where the noise come from !
Vcc
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Which impedance do we need ?
0
10
20
30
40
50
60
Level [dBµV/m]
30M 40M 50M 70M 100M 200M 300M 400M 600M 1G
Frequency [Hz]
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Differential noise filter: SMD-Ferrite WE-CBF
(Chip Bead Ferrite)
SMD-Ferrite
WE - CBFLink Aufbau
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Impedance: SMD-Ferrite (Chip Bead)
XL(NiZn)
Advantage of SMD-Ferrites:wideband, frequency-dependent
Absorber for RF-noise in the frequencyrange 10 MHz ... > 2GHz
with very low DC-Resistance (< 0,8 Ohm max. !)
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Insertion Loss Model
Equivalent circuit of source
Equivalent circuit of system impedance
)(log20 dBinZZZZZABA
BFA
+++=Insertion Loss =>
ZA ZF
ZBU1U0 U2
Equivalent circuit of Filter
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Simulation Model Cap
Simulation Model Fer.
The real world........ !
Equivalent Circuit of Filter-ComponentsEquivalent circuit of source
Equivalentcircuit of load
for Inductor and Capacitor onecan find Simulation-Models
? ?
source
Noisesource
device
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Practical figures for ZA / ZB
* Groundplanes : Impedance range 1 ... 2 Ω
* VCC-Distribution: Impedance range 10 ... 20 Ω
* Video-/ Clock-/ Dataline: Impedance range 50 ... 90 Ω
* Long Datalines: Impedance range 90 ... >150 ΩWith this we can make a first decision of a Ferrite-Impedance ZFwhich would suppress noise in our application :
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Which Impedance ZF is needed ?
Example 1: required attentuation = 20dB @ 200 MHz
VCC-Distribution
System impedance ca. 10 Ohm
180Ω
=> goto Nomogramm:
180 Ω => choise: 220 Ω
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case 1: Attentuation reached
The initialsetup that System Impedance isaround 10 Ohm at 200 MHz istrue !
220Ω
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case 2: More Attentuation reached
Measurement of e.g. 40dBwith Ferrit.
The System-impedance ZA and ZB aremuch lower (at around 1 Ohm)!
220Ω
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Analyse of the results
0
10
20
30
40
50
60
Level [dBµV/m]
30M 40M 50M 70M 100M 200M 300M 400M 600M 1G
Frequency [Hz]
--- : Perfect 20 dB attenuation
--- : Only 10 dB attenuation ??
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case 3: less attentuation reached
Measured onlye.g. 10dBwith Ferrite.
The System-impedances ZA and ZB aremuch higherthan expected(around 50 Ohm) !
OR
Additional coupling pathesnot taken intoaccount !
220Ω
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Insertion Loss vs. Impedance of Source/ Load (ZA / ZB)
A = -32 dB max.with ZA = ZB = 10 Ω = constant
A = -18 dB max.with ZA = ZB = 50 Ω = constant
A = - 8 dB max.with ZA = ZB = 200 Ω = constant
A = - 3 dB max.with ZA = ZB = 1000 Ω = constant
with ZA = ZB = 5000 Ω =constantno effect in filtering !
SMD-Ferrite ZF = 600 Ohm @ 100 MHz
Frequency (Hz)
Inse
rtio
n Lo
ss (
dB)
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EMI Problem: Integrated DC/DC Converter
Common Mode Choke and 2 EMI-Ferrites: because of capacitive over coupling (Profibus to 24 V-DC !!)BURST before : 0,9 kV; after up to 3,5kV OK
CMC 2x2000µH 0,6A 744221 WE-SL2 Würth
SMD-Ferrite Z=1200Ohm 0,2A 74279216 WürthFR-PM-3
EMI Problem: Capacitive Coupling Burst-Test
Integrated DC/DC converter with transformer
C coupling ~ 10 pFin outin out
Input : 1 kV Burst / rise time 5 nsOutput ?
!21051000 ApFnsV
dtdvdi Ccoupling ==∗=
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Recommended EMI-Filter circuits
Suggested Circuits
ATTENTION !Self-Resonant-Frequencyof Components !!!
smaller C = higher SRF
If you choose SMD-Ferrite instead of Inductor L = no Resonance with C = broadband filtering
Source Impedance Load Impedance
low
low low
high
high
high
high orunknown
low orunknown
low orunknown
C
L CC
L
L
C
L
high orunknown
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Noise source
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Filter Topologies
50 Ohm Ref. Line
3xC Capacitance Filter
„L“Filter with SMD Ferrite„L-C“ Filter with SMDFerrite und Capacitor
„PI“ Filter
„T“ Filter
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Filter Topologies
50 Ohm Ref. Line
3xC Capacitance Filter
„L“Filter with SMD Ferrite
„L-C“ Filter with SMD Ferrite und Capacitor
„PI“ Filter
„T“ Filter
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SWITCHER CAD III / Simulation
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The „L“ Ferrite –Filter
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Simulation in LTSpice/SwitcherCADIII
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Insertion Loss
-40
-35
-30
-25
-20
-15
-10
-5
0
1 10 100 1000
Frequenz in MHz
in d
B
Ferrite-Filter Simulation modell)
The „L“ Ferrite –Filter
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Ferrite –Filter: Measured vs. Simulation
Insertion Loss
-40
-35
-30
-25
-20
-15
-10
-5
0
1 10 100 1000
Frequenz in MHz
in d
B
Ferrite-Filter (Insertion Loss)Ferrite-Filter Simulation modell)
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Ferrite –Filter: Measuring vs. Simulation
Insertion Loss
-120
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
Ferrite-Filter (Insertion Loss)Ferrits-Filter Simulation modell)Ref.-Meas. (Spectrum Analyzer)
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Ferrite –Filter: Measuring vs. Simulation
Insertion Loss
-120
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
Ferrite-Filter (Insertion Loss)Ferrite-Filter Simulation modell)Ref.-Meas. (Spectrum Analyzer)Ferrite-Filter (Spectrum Analyzer)
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Parallel capacitors
C1= 1nF
C2=10nF
C3=100nF
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Parallel capacitors resonancy
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Paralleled Caps on IC (74HCT)/ NO Ferrite Bead
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Paralleled Caps (w/o Ferrite Bead ) on IC 74HCT
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Paralleled C with Ferrite Bead on IC (74HCT)
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Attenuation
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1 10 100 1000
Frequency in MHz
in d
BC-Filter (Simulationsmodell)
Parallel capacitors
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C-Filter: Measure vs. Simulation
Dämpfung
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1 10 100 1000
Frequenz in MHz
in d
B
C-Filter (Einfügedämpfung)C-Filter (Simulationsmodell)
Attenuation
Frequency in MHz
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Dämpfung
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
C-Filter (Einfügedämpfung)C-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)
C-Filter: Measure vs. Simulation
Attenuation
Frequency in MHz
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Dämpfung
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
C-Filter (Einfügedämpfung)C-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)C-Filter (Spectrum Analyzer)
C-Filter: Measure vs. Simulation
Attenuation
Frequency in MHz
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Basic Design-Rule of EMC-Filters
Low DC-Resistance; high Absorption forRF-noise; no SRF-Point
Low ESR; „zero“-Ohm-Path to GND for RF-noisestabilzie VCC for Pulse-Currents
L1
C1
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Filtercircuit: Lowpass-Filter (ideal)
This is what we learn in the school....
L1
C1
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Step 1: Lowpass-Filter with real Capacitor .....
L1
Cs
Ls
Rs
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Step 2: Lowpass-Filter with real Capacitor and real Inductor /SMD-Ferrite
Lp
Cs
Ls
Rs
Rp
Cp
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Step 3: Lowpass-Filter with real Capacitor ,real Inductor and connection to GND
Capacitor with 1mm wire ~ 1 nH1 via ~ 0.5 nH
Lp
Cs
Ls
Rs
Rp
Cp
1 mm ~ 1nH
1 via ~ 0.5 nH0.5 nH @ 100 MHz = 0.314 Ω
0.5 nH @ 1 GHz = 3.14 Ω !
PCB via
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Layout and Vias
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good
vias to ground
bad
Layout for Ground
IC2aIGND
The GND-Potential is affectedby current driven throughground-pin of semiconductor !
IGND
IC2aSeparated ways for RF-currentof C2a and semiconductor
More vias = smaller DCR/L
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Grounding / Layout
LC-Lowpassfilter Layout Lowpassfilter
Why will this filter not work properly at RF-Frequencies ?
Ground-Level
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Layout
Inductive coupling
Capacitive coupling
Bypass for noise
too long tracks
Contraction for RF
more vias to GND= low ohmic= smaller inductance
Connection to Case
bad solution optimized
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LC-Filter
L=742 792 093
C=100nF
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The LC-Filter
Dämpfung
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1 10 100 1000
Frequenz in MHz
in d
B
LC-Filter (Simulationsmodell)
Attenuation
Frequency in MHz
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Dämpfung
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1 10 100 1000
Frequenz in MHz
in d
B
LC-Filter (Einfügedämpfung)LC-Filter (Simulationsmodell)
LC-Filter: Measured vs. Simulation
Attenuation
Frequency in MHz
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Dämpfung
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
BLC-Filter (Einfügedämpfung)LC-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)
Attenuation
Frequency in MHz
LC-Filter: Measured vs. Simulation
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Dämpfung
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
LC-Filter (Einfügedämpfung)LC-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)LC-Filter (Spectrum Analyzer)
Attenuation
Frequency in MHz
LC-Filter: Measured vs. Simulation
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The Pi-Filter
C1=1nF
L=742 792 093
C2=100nF
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Improvement for VCC-Decoupling with π-Filter
IC
VCC
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Calculation of Minimum Decoupling-Capacitor
nFmVnsmA
dUdtdICS 1200
540 =⋅=⋅=Bsp: allowed Voltage-Drop 200mV at Pulse-Current of @ t = 5ns:
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Dämpfung
-120
-100
-80
-60
-40
-20
0
1 10 100 1000
Frequenz in MHz
in d
B
Pi-Filter (Simulationsmodell)
Attenuation
Frequency in MHz
The Pi-Filter
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Dämpfung
-120
-100
-80
-60
-40
-20
0
1 10 100 1000
Frequenz in MHz
in d
B
Pi-Filter (Einfügedämpfung)Pi-Filter (Simulationsmodell)
Pi-Filter: Measured vs. Simulation
Attenuation
Frequency in MHz
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Dämpfung
-120
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
Pi-Filter (Einfügedämpfung)Pi-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)
Attenuation
Frequency in MHz
Pi-Filter: Measured vs. Simulation
-
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Dämpfung
-120
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
Pi-Filter (Einfügedämpfung)Pi-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)PI-Filter (Spectrum Analyzer)
Attenuation
Frequency in MHz
Pi-Filter: Measured vs. Simulation
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Improvement for VCC-Decoupling with π-Filter
Description of internal parasitics by ICEM-project (see IEEE publications / Google)
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ICEM Model: parasitics of IC (74HCT)
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ICEM Model: 1nF/ 100nF Caps only (no Ferrite Bead)
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ICEM Model: 1nF/ 100nF and Ferrite Bead 74279213
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Probing & Practical Tip
68 mVpp with 3.3 µF + 1µH + 3.3 µF input Cap
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EMI: Conducted Emission (w/o input filter)
LT3481EMSE Demo Board24V to 3.3V @2A fsw=500kHzCEM 0.15 – 30 MHz
Test without EMC filter:Peak 82dBµV
→ 26dB above limit !
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EMI: Conducted Emission w filter
Test with additional L=10uH,C=3.3uF 50V 1210 input filter
Peak=42dBµV/m ∅=32dBµV/m
Peak & ∅ 14dB below limit
Ferrite bead High ESR Elco to damp cable
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EMI: Radiated Emission
10dB attenuator in software !result should be 10dB lower
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The T-Filter
L1=742 792 040
C=100nF
L2=742 792 092
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Optimisation of T-Filter for 500 MHz (Notch)
SMD-Capacitor
SMD-Ferrite SMD-Ferrite
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Pratice-Tip: SRF of SMD-Capacitors
Example 1:Filter with maximum attentuation at f = 500 MHz in a system ZA = ZB = 100 Ω = konst.;T-Filter Step 1:
choose C with SRF @ 500 MHz
=> Nomogramm:
size 1206 ; C = 68 pF
68 pF
Step 2:calculation of Ls
SRF = 500 MHz :
nHCL resSS49,11 2 =⋅= ω
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Simulation-Model: SMD-Ferrite
Rp = 685 ΩCp = 1,2584 pFLp = 1,4675 nHRDC = 0,30 Ω
Rp = 125 ΩCp = 0,1834 pFLp = 0,2000 nHRDC = 0,30 Ω
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Simulation-Result for T-Filter
Only C = 68 pF
more attentuation with SMD-Ferrite
Broadband attentuation by using SMD-Ferrite
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The T-Filter
L1=742 792 040
C=100nF
L2=742 792 092
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Dämpfung
-120
-100
-80
-60
-40
-20
0
1 10 100 1000Frequenz in MHz
in d
B
T-Filter (Simulationsmodell)
Attenuation
Frequency in MHz
The T-Filter
-
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Dämpfung
-120
-100
-80
-60
-40
-20
0
1 10 100 1000
Frequenz in MHz
in d
BT-Filter (Einfügedämpfung)T-Filter (Simulationsmodell)
T-Filter: Measured vs. Simulation
Attenuation
Frequency in MHz
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Dämpfung
-120
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
T-Filter (Einfügedämpfung)T-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)
Attenuation
Frequency in MHz
T-Filter: Measured vs. Simulation
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Dämpfung
-120
-100
-80
-60
-40
-20
0
20
1 10 100 1000
Frequenz in MHz
in d
B
T-Filter (Einfügedämpfung)T-Filter (Simulationsmodell)Ref.-Messung (Spectrum Analyzer)T-Filter (Spectrum Analyzer)
Attenuation
Frequency in MHz
T-Filter: Measured vs. Simulation
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You want to know more ??
Look at our Book:
Chap.1: Basicskeep it simple, stupid
Chap.2: ComponentsDescriptions, Applications, Simulation Models and many more
Chap.3: Filter-CircuitsDesign, Grounding, Layout, Tipps
Chap.4: ApplicationsCircuit, suggested parts, Layout
Chap.5: Appendicesfrom A to Z
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FR-PM-3
You want to know more ??
Look at ABC of Transformers:
Chap.1: Basic Principleskeep it simple and stupid
Chap.2: ApplicationsDescriptions, Applicationsand many more
Chap.3: Step-by-Stepbuild a transformer for the mostimportant switching topologies
Chap.4: Directoriesin depth explanations andfrom A to Z