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Designing High Performance, Low
Cost Tunable Bandpass Filters
Authored by:
Stefano Biagiotti, Giancarlo Guida, Alain MichelAnsoft Corporation
Ansoft 2003 / Global Seminars: Delivering Performance
Presentation #13
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Overview
w Short description of previous generation filter designsw Electrical performances, technology, highlights - lowlights
w Filter enhancement
w New performances, cost reduction, reproducibility
w Implementation
w Filter synthesis
w Tuning range verification
w Sensitivity analysis
w Completion of the circuit
w NL analysis
w Statistical analysis
w EM analysis
w HFSS + DESIGNER
w Benefits
w Conclusions
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Old Filter: Physical Implementation
PCB with 16 diodes
mounted by hand
Handmade coil (Ag. 2mm)
Resistive TRIMMERS
CapacitiveTRIMMERS
Filter to redesign
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Old Filter: Electrical Performance(for Each Stage)
w Frequency range 118 - 137MHz
w Bandwidth 5MHz
w Insertion Loss > -2.5dB
w Return Loss < -15dB
w Out of band rejection > -45dB @ F0 20MHz
w Voltage tuning 1 - 10V
w Allowed max input power > 25dBm
Number of devices producedNumber of devices producedper year about 300per year about 300
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Old Filter: Highlights, Lowlights
w Highlightsw High value of quality factor
w Electrical performances well matched
w Mechanical dimensions
w Lowlights
w 90% hand-made
w Manual filter tuning needed for each device
w Reproducibility
w Production time
Average time to manufactureAverage time to manufacture
a single device was 1.5 houra single device was 1.5 hour
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Reasons to Modernize
w Obsolescence of componentsw Obsolescence of components used for the main project
and new product specification involved also redesigning atunable pass band filter.
w Costsw The new Radio Ground Station had to cost much less;
which provided more incentive to redesign the filter.
w Outsourcingw Devices require high reproducibility in order to be
manufactured by outsourcing, hence, designers mustavoid manual tuning operations whenever possible.
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New Filter Specifications(for Each Stage)
w New performances:
w Frequency range 108 - 156MHz
w Bandwidth < 10MHz
w Insertion Loss > -2.5dB (-3dB 108 - 118MHz)
w Return Loss < -15dB
w Out of band rejection < -45dB @ F0 + 42.8MHz
w Voltage tuning 2 - 18V
w Allowed max input power > 25dBm
w Cost reduction:w Minimize manual tuning; automate manufacturing
w Reproducibility:
w Technology selection
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New Filter Topology
w Why Combline Transformer topology?
We can tune the
filter with some
VARICAP diodes
One of the best topologies for small tolerances!!
With MS Tech.
we avoid one of
the manual tuning
processes
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Filter Synthesis: Enter specifications
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Port1
Port2
Filter Synthesis Output
We can complete thelayout by changing the
CAPs footprint...
Port1 Port2
4321
C1
Q=Q1
C1
Q=Q1
Layout Output
Schematic Output
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CAPs properties window from layout
Footprint Library
Filter Synthesis CompletionChanging the current footprint of
the capacitors
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Port1 Port2
4321
C1
Q=Q1
C1
Q=Q1
Filter Synthesis: Circuit Simulation
Simulation results of circuit
created from Filter Synthesis
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Tuning Verification: Capacitor range
The tuning is used to validate the frequency range of the filter.
Choose Sweep/Accumulate or Real Time tuning
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Tuning Verification: Varicap Bias range
We can also complete the schematic
by changing the CAPs Q factor...
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Sensitivity Analysis
124.9MHz 134MHz
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Sensitivity [email protected]
0.04dB
0.6dB0.25dB
7.5dB
S2 +/-0.1mm
w1 +/-0.1mm
w2 +/-0.1mm
W2 critical size!
S1 +/-0.1mm
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Circuit Completion: Schematic and Layout
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Circuit Completion : NL Simulation
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Circuit Completion: Tuning biasVs=2.3VF=108MHz
Vs=16.5VF=156MHz
Vs=7.3VF=130MHz
S21
S11, S21, S22
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Circuit Completion : Layout
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Statistical Analysis: Define Setup
Add parameters to
Statistical Analysis
Add Statistical
Analysis setup
Define Goal
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Statistical Analysis Freq=108MHz
Yield=55% for S11
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Statistical Analysis Freq=156MHz
Yield=46% for S11
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EM Analysis: full board simulation
Automatic generation of the full board forAutomatic generation of the full board for
EM cosimulation or cooptimizationEM cosimulation or cooptimization
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EM Analysis: Compare Simulation
Port1 Port2
PBFLayout
n2 n11
n111 n214
n118 n223
n125
n138 n239
n247 n248
n149 n150
n261 n162
n163 n264
n265
n178 n180
n283 n284
n185 n187
U1EM Layout
BB439
D1
BB439D2
BB439D3
BB439
D4
BB439D5
BB439
D6
BB439
D7
BB439D8
RCI_0
603_
4703G
47
0kOhm
RCI_0603_
4703G
470kOhm
GRM39
C0G120J050
12pF
GRM39
C0G120J050
12pF
+-
Vs
+-
Vs
EM setup Analysis andEM setup Analysis and
Frequency areFrequency are
automatically set or definedautomatically set or defined
by the userby the user
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Ansoft Designer + HFSS
How can we test the prototype?
SMA Connector
We need a 3D full wave
model to take in count itseffects on the device...
HFSS v9 Model
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Ansoft Designer + HFSS
SMA effects
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DESIGNER + HFSS
HFSS results for SMA connectorHFSS results for SMA connector
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New Filter: Physical Implementation (1)
Data exportData exportfor direct manufacturingfor direct manufacturingExtended Gerber and NC Drill filesExtended Gerber and NC Drill files
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New Filter: Physical Implementation (2)
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Benefits
w Low cost device (about 20 EURO)
w Production time 10min (compared to 1.5 hour)!
w Extremely reproducible (no manual tuning)!
w Electrical performances matched very well!
Number of devices producedNumber of devices produced
per year about 1000per year about 1000
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Conclusionsw We have presented a design and development of a MS PBF using
ANSOFTs EDA software.w With DESIGNER v1.1 we have been able to do:
w Filter synthesis
w Linear simulation (S-parameter extraction)
w Tuning
w Non Linear simulation (VARICAPs effect, Intermodulation)
w Statistical Analysis
w Layout planar EM analysis
w Easy integration in a design of a 3D full wave simulation (SMAconnector) made in ANSOFT HFSS
By applying software tools early in the development process,By applying software tools early in the development process,problems can be quickly identified and resolved prior toproblems can be quickly identified and resolved prior to
production, greatly decreasing time to market!!production, greatly decreasing time to market!!