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www.beTheSignal.comCompany Confidential 1
PPTPPT--313 QUCS a Getting Started Guide313 QUCS a Getting Started Guide
Eric BogatinEric Bogatin
Signal Integrity EvangelistSignal Integrity Evangelist
Teledyne LeCroyTeledyne LeCroy
www.beTheSignal.comwww.beTheSignal.com
Jan 2014
Copes can be downloaded from www.beTheSignal.com (PPT-313)
www.beTheSignal.com 2
Outline
� Simulation: a blessing and a curse
� Practice Safe Simulation: Rule #9
� Getting started with QUCS
� Five examples:
� Signals in the time and frequency domain
� A TDR
� Reflections, terminations and topologies
� An impedance analyzer
� A VNA
www.beTheSignal.com 3
Types of Numerical Simulation Tools
Signal Analysis: (predicting signal
waveforms based on numerical
analysis): excel, Matlab,
MathCAD, SI Studio;.
Circuit Simulation: (SPICE:
simulating voltage and currents
based on circuit elements)
Electromagnetic Simulation (modeling: converting
geometry and materials into electrical models): HFSS,
CST, Momentum, Simbeor, Sigrity, ;.
1 2 3 4 5 6 7 8 90 10
-30
-20
-10
-40
0
freq, GHz
Diffe
rential R
esp
onse,
dB
Input geometry and materialsSolve Maxwell’s equations,
output fields, currentsOutput S-parameters, model
parameters
www.beTheSignal.com 4
The Power of Simulation
� Explore design space with virtual prototypes
� Convert physical design into electrical models
� Explore performance of electrical models
� Answer “;it depends” questions
� maximum data rate a channel will support
� selecting optimize capacitor values
� Faster time to an optimized design
� Learn Signal Integrity by doing it
www.beTheSignal.com 5
QUCS: Quite Universal Circuit Simulator
� A SPICE like circuit simulator
� It is NOT a modeling tool
� You have to supply the circuit models and
parameter values
� If you can draw the circuit (schematic) QUCS will
predict the voltages and currents in time or
frequency
� The perfect introduction to simulations
www.beTheSignal.com 6
Why Commercial Simulators
� QUCS is “open source” (free)
� “Free” comes at a price
� What you can pay up for:
� more features, capability, models, elements,
� ease of use
� support
� automation, scripting
� faster time to correct answer
� If QUCS is adequate for your application, you can’t beat free.
www.beTheSignal.com 7
Learning Modes
� Read it
� Hear it
� Write it
� Teach it
� Do it
� Measure real prototype
� Simulate virtual prototype
Signal and Power
Integrity-
Simplified
www.beTheSignal.com 8
The Danger of Simulation
Just because there are a lot of digits or it goes
to high frequency, doesn't mean it’s an accurate
prediction of the real world
www.beTheSignal.com 9
Practice Safe Simulation
www.beTheSignal.com 10
Download Instructions
� Open source: http://qucs.sourceforge.net/
� www.beTheSignal.com: under PPT-313
and ECEN 5224
� courtesy copy of the software
� installation instructions
� some manuals
� five examples projects
www.beTheSignal.com 11
Installation Process
� Open downloaded zip folder
� Review readme file
� Install QUCS
� Move the _prj folder to the .QUCS directory
� Re-start QUCS
� Good to go
www.beTheSignal.com 12
Example #1: Spectrum of Signals
� Orientation
� zoom navigation
� parameters (press return to lock in values)
� simulation
� displays
� Rise time and Spectrum
www.beTheSignal.com 13
Example #2: a TDR
V_reflected = V_TDR_10psec – V_incident
V_incident = 1 v
www.beTheSignal.com 14
Example #3: Terminations and Reflections
www.beTheSignal.com 15
Example #4: Impedance Analyzer
V(f) = I(f) x Z(f)
www.beTheSignal.com 16
Example #5: A Network Analyzer (and S-parameter viewer)
www.beTheSignal.com 17
Next Steps
� Download QUCS
� Download the 5 example projects
� Now you try it;