passive component analysis
TRANSCRIPT
Passive Component Analysis
OMICRON Lab Webinar Nov. 2015
Page 2Smart Measurement Solutions®
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Page 3Smart Measurement Solutions®
Agenda
• Why do we analyze passive components
• How to measure component impedance
• A detailed look at a capacitor
• Inductor and transformer
• Filter simulation vs. real world
• Summary
Page 4Smart Measurement Solutions®
Passive Components
• Essential parts in analog circuits
• Inductor and capacitor used e.g. to store energy or to
create filter circuits
Inductor: 𝑣 𝑡 = 𝐿𝑑𝑖 𝑡
𝑑𝑡𝑋𝐿 = 𝜔𝐿
𝑉
𝐼= 𝑍𝐿 = 𝑗𝜔𝐿
Capacitor: 𝑖 𝑡 = 𝐶𝑑𝑣 𝑡
𝑑𝑡𝑋𝐶 =
−1
𝜔𝐶
𝑉
𝐼= 𝑍𝐶 =
1
𝑗𝜔𝐶
Page 5Smart Measurement Solutions®
Capacitor:• Plates are resistive
• Rolling of foils creates inductance
• Insulator not lossless
Theory and Reality
• Theoretically inductor and capacitor are purely reactive
elements No resistive behavior and therefore lossless
• In reality parasitics can strongly influence the real
behavior especially at higher frequencies
Examples:
Inductor:• Wire has resistance
• Windings form electric field
• Core is not lossless
Page 6Smart Measurement Solutions®
Equivalent Circuits
• Are used to model the real behavior of the components
• Different complexity of models
− 1st order models are valid for one frequency
Single Frequency Mode in BAS calculates R, L and C
Frequency Sweep Mode calculates R, L and C over frequency
0
2
4
6
8
10
0
2n
4n
6n
8n
10n
5M 10M 15M 20M 25M 30M 35M 40M
TR
1/O
hm T
R2
/H
f/HzTR1: Rs(Impedance) TR2: Ls(Impedance)
Page 7Smart Measurement Solutions®
Equivalent Circuits
• Higher complexity models are valid for a frequency range
− 2nd Order equivalent circuits for inductor and capacitor
− 3rd Order models (e.g. quartz crystal or piezo element)
• Parameter identification requires manual
work or e.g. curve-fitting procedure
≙ ≙
see Application Note:
Equivalent Circuit Analysis of Quartz Crystals
https://www.omicron-lab.com/application-notes/
Page 8Smart Measurement Solutions®
Bode 100 Impedance Measurement Methods
• Direct Measurements
− One-Port Reflection
− Impedance Adapter (3-port technique)
− External bridge (e.g. high impedance bridge)
• Indirect Measurements (via Gain)
− Shunt-Thru (2-port technique)
− Series-Thru (2-port technique)
− Voltage-Current Gain (3-port technique)
Page 9Smart Measurement Solutions®
Direct Measurement MethodsOne-Port
Recommended for 0.5 Ω - 10 kΩ
Impedance Adapter
Recommended for 20 mΩ - 600 kΩ
External Bridge / Coupler
Range depends on bridge
Page 10Smart Measurement Solutions®
Indirect Measurement MethodsSeries-Thru
Recommended for 1 kΩ < 10 MΩ
𝑍𝐷𝑈𝑇 = 100 Ω ⋅1 − 𝑆21𝑆21
Shunt-Thru
Recommended for 1 mΩ - 10 Ω
𝑍𝐷𝑈𝑇 = 25Ω ⋅𝑆21
1 − 𝑆21
𝐺𝑎𝑖𝑛 =𝑉𝐶𝐻2𝑉𝐶𝐻1
=𝑉
𝐼= 𝑍𝐷𝑈𝑇
Voltage Current Gain
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Impedance Range Overview
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Why is it important to measure capacitors?
• A capacitor is NEVER just a capacitor
• Capacitor ESR influences the phase margin of power supplies
• Capacitor ESR influences the output ripple at the switching
frequency of a SMPS
• ESR can change over Frequency
• Capacitors are inductors above
their resonance frequency
Page 13Smart Measurement Solutions®
What does the data sheet tell us?
220 µF aluminum capacitor
C = 220µF (± 20%)
𝐸𝑆𝑅 =tan 𝛿
𝜔𝐶=
0.12
2𝜋 ⋅ 120𝐻𝑧 ⋅ 220µF= 0.72 Ω@ 120 𝐻𝑧
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This is what the measurement tells us
-100
-50
0
50
100
102 103 104 105 106 107
TR
2/°
f/HzTR2: Phase(Impedance)
Phase
-210
-110
010
110
102 103 104 105 106 107
TR
1/O
hm
f/HzTR1: Mag(Impedance)
Impedance
Capacity
f/Hz TR1/Ohm
Cursor 1 120,000 233,077m
1
-210
-110
010
102 103 104 105 106 107
TR
1/O
hm
f/HzTR1: Rs(Impedance)
ESR
Page 15Smart Measurement Solutions®
Calibration
Open
Short Load
Page 16Smart Measurement Solutions®
User Calibration / Probe Calibration
• User Calibration (User Range Calibration)
Calibrates at exactly the frequencies that are currently measured
+ No interpolation, suitable for narrowband probes
• Probe Calibration (Full Range Calibration)
calibrates at pre-defined frequencies and interpolates in-between
+ Calibration does not get lost when frequency range is changed
Page 17Smart Measurement Solutions®
Detailed Example available
-5m
-4m
-3m
-2m
-1m
0
1m
2m
3m
4m
5m
101 102 103 104 105 106
TR
2/F
f/HzTR2: Cs(Impedance)
-210
-110
010
101 102 103 104 105 106
TR
1/O
hm
f/HzTR1: Rs(Impedance)
see Application Note:
Capacitor ESR Measurement with Bode 100 and B-WIC
https://www.omicron-lab.com/application-notes/
Page 18Smart Measurement Solutions®
Fitting Model to Measured Impedance
• Various methods
available
• We use curve-fitting
• A Preview tool is
available on
request
Page 19Smart Measurement Solutions®
Simulation vs. Measurement
-210
-110
010
110
210
310
-90
-60
-30
0
30
60
90
101 102 103 104 105 106 107
TR
1/O
hm T
R2
/°
f/HzTR1: Mag(Impedance) TR2: Phase(Impedance)
Page 20Smart Measurement Solutions®
Voltage sensitivity of capacitors
see Application Note:
DC Biased Impedance Measurements
https://www.omicron-lab.com/application-notes/
Page 22Smart Measurement Solutions®
Why should we measure inductors?
• An inductor is NEVER just an inductor
• AC resistance <> DC resistance
− skin effects
− “Eddie Currents”
• Inductors have resonance frequencies
• Inductors with magnetic cores can have core losses
Page 23Smart Measurement Solutions®
What does the data sheet tell us?
33 µH shielded power inductor
H = 33µH (± 20%) @ 1 kHz𝑅𝐷𝐶=0,049 𝛺 (𝑡𝑦𝑝.)𝑅𝐷𝐶=0,057 𝛺 (𝑚𝑎𝑥.)fres = 11 MHz
Page 24Smart Measurement Solutions®
f/Hz TR2/H
Cursor 1 292,486 33,019µCursor 2 101,789k 30,551µ
C2-C1 101,496k -2,468µ
1 2
-200u
-100u
0
100u
200u
300u
102 103 104 105 106 107
TR
2/H
f/HzTR2: Ls(Impedance)
f/Hz TR1/Ohm
Cursor 1 292,486 40,049mCursor 2 101,789k 759,543m
C2-C1 101,496k 719,494m
1 2
-110
010
110
210
310
410
102 103 104 105 106 107
TR
1/O
hm
f/HzTR1: Rs(Impedance)
f/Hz TR2/°
Cursor 1 13,362M -5,879
1
-200
-150
-100
-50
0
50
100
150
200
102 103 104 105 106 107
TR
2/°
f/HzTR2: Phase(Impedance)
f/Hz TR1/Ohm
Cursor 1 13,362M 40,673k
1
-110
010
110
210
310
410
102 103 104 105 106 107
TR
1/O
hm
f/HzTR1: Mag(Impedance)
This is what the measurement tells us
Impedance
Inductance
ESR
Phase
Page 25Smart Measurement Solutions®
Flyback Transformer Leakage Inductance
• Not all flux generated by the primary winding is coupled to the secondary winding
− some flux leaks
− some contributes to core losses
• Represented by a series inductance in the circuit
• Leakage inductance creates a voltage spike when turning off current through primary side (flyback converter)
Page 26Smart Measurement Solutions®
Measuring Leakage Inductance
Leakage inductance is measured by shorting all other
windings except the primary winding
-110
010
110
210
310
410
510
103 104 105 106 107
TR
1/O
hm
f/HzTR1: Mag(Impedance) Memory 1 : Mag(Impedance)
0
2u
4u
6u
8u
10u
12u
103 104 105 106 107
TR
2/H
f/HzTR2: Ls(Impedance)
Leakage inductance is not constant over frequency
Secondary open Secondary shorted Leakage inductance
Page 27Smart Measurement Solutions®
LC Filter Bode Diagram
Passband
Resonance
(Double-pole)
Stopband
-40dB/Decade
-180° Phase
Simulation in LTSpice:
Page 28Smart Measurement Solutions®
LC Filter Test board
Measuring the voltage transfer function 𝐻 𝑗𝜔 =𝑉𝑜𝑢𝑡
𝑉𝑖𝑛
Page 29Smart Measurement Solutions®
Measurement vs. Simulation
Measurement
Simulation
• Stopband is
different
• Phase does not
reach -180°
• Second resonance
at 30 MHz
parasitic effects
Page 30Smart Measurement Solutions®
-140
-120
-100
-80
-60
-40
-20
0
20
-180
-150
-120-90-60
-300
30
60
90120
150
180
101 102 103 104 105 106 107
TR
1/d
B TR
2/°
f/HzTR1: Mag(Gain) TR2: Phase(Gain)
LC Filter Including Parasitics
• much better fit
between
simulation and
measurement
• Could be further
improved by better
component
models
Page 31Smart Measurement Solutions®
Reducing Output Ripple
2 x 10µF ceramics adds 20dB attenuation at 300 kHz
f/Hz TR1/dB
Cursor 1 290,070k -62,575
1
-80
-60
-40
-20
0
101 102 103 104 105 106 107
TR
1/d
B
f/HzTR1: Mag(Gain) Memory 1 : Mag(Gain)
Imroved stop
band
performance
at 300 kHz
(e.g. switching
frequency)
Page 32Smart Measurement Solutions®
Summary
• Component parasitics are
important to understand real life
circuit behavior
• Models considering parasitics
allow better simulation
• Measuring components can tell us more
than the data sheet says
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