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Have You Tried the New Transmission Line Library (rfTlineLib)?

Comments(2)Filed under: Spectre RF, spectreRF, RFIC, RF Simulation, RF, SpectreRF tutorials, Wilsey, transmission line, rfTlineLib

Happy New Year!  

Have you tried the new Transmission Line Library (rfTlineLib) yet?

In case you missed it, rfTlineLib was introduced in IC 6.1.6 ISR1 plus MMSIM 12.1.1 -or- MMSIM13.1.

You may wonder....Why should I use the new rfTlineLib ?   Well.....here are a few reasons:

  • Accurate and robust
  • Consistent between time and frequency-domain: Causal modeling approach ensures identical results in frequency vs. time domain simulations
  • Easy to use: Graphical stack-up concept makes the editing of substrate parameters more efficient and less error prone

The new rfTlineLib contains wideband-accurate transmission line models in multi-conductor microstrip and stripline configurations. Based on frequency-dependent per-unit-length parameters calculated by a 2D quasi-static electromagnetic solver, the models are both integrated in Virtuoso ADE and accessible from stand-alone Spectre netlists. The use model has been enhanced to include an interactive, graphical stack-up editor for storing substrate geometry and material properties.

New rfTlineLib models, such as mlin and slin, are based on rigorous EM simulations and include state-of-the-art descriptions of dielectric and conductor losses. Their applicability extends to long transmission lines and wide frequency range. The models have been tested extensively against standard industry benchmarks and 3D EM models, matching them within 1% or better.

The runtime simulation performance of new rfTlineLib models is comparable to the legacy lumped approximations. The use of EM-based transmission line parameters means that, in general, the initial extraction takes considerably longer, a few seconds in typical cases. However, instance and cross-section based caching makes EM extraction a one-time cost. As a result, in typical use, the overall simulation performance remains highly efficient.

rfTlineLib transmission lines are based on Spectre mtline technology and are netlisted as instances of mtline. mtline has been enhanced significantly to support rfTlineLib. 

  • Improvements to EM solver accuracy. The solver is now within 1% of established benchmarks.
  • New Spectre primitives -- including stackup, dielectric and conductor - and new mtline parameters, to support a common substrate definition and the ability to reference it from mtline
  • New frequency-dependent models of dielectric losses, including Debye, Wideband Debye, and table-based
  • The Hammerstad surface roughness model for enhanced modeling of conductor losses
  • EM solver speed improvements

The rfTlineLib library (located in the IC6.1.6 stream at $CDSHOME/tools/dfII/samples/artist/rfTlineLib ) is divided into the following categories: 

  • Everything:  A complete list of all components in the library
  • Uncategorized:  Contains one item - the stackup.The stackup defines shared substrate and conductor parameters of the PCB/MMIC/IC and is referenced by all other models. 

The geometric properties include layer order and thicknesses while the material properties include dielectric constants, loss tangent, conductance, Debye model, frequency table of the complex dielectric constants, etc. The stackup offers several pre-configured and commonly used layer stacks and also offers the ability to define custom substrates.  This is done with an easy-to-use graphical editor.  These new cells reference the common substrate definition without the need to re-enter shared parameters.

  • Behavioral:    clin and tlinp (clin represents an ideal two-conductor coupled transmission line. tlinp represents a lossy single-conductor transmission line. )
  • Transmission Lines:
    • maclin: asymmetric 2-conductor coupled microstrip
    • mclin: coupled 2-conductor microstrip
    • mlin: single-conductor microstrip
    • nclin: n-conductor transmission line
    • sclin: coupled 2-conductor stripline
    • slin: single-conductor stripline

Here's the view from the Library Manager:

rfTlineLib transmission line

  • Discontinuities:  
    • mbend, sbend: microstrip, and stripline mitered arbitrary angled bend
    • mbend2, sbend2: microstrip, and stripline mitered 90 degree bend
    • mcorn: microstrip corner
    • mcurve, scurve: microstrip, and stripline curves
    • mcros, scros: microstrip and stripline crosses
    • mloceff, sloceff: microstrip and stripline open-circuit effects
    • mtee, stee: microstrip and stripline T-junctions
    • mstep, sstep: microstrip and stripline step discontinuities

And here's the view from the Library Manager:

rfTlineLib discontinuities 

  • Obsolete: Cells which are no longer recommended for use and are kept strictly for legacy reasons.   See the  Virtuoso Spectre Circuit Simulator RF Analysis Library Reference, Product Version 13.1 for more information.


The new rfTlineLib library is easy to use.   Just follow these simple steps:

1.  Insert a stackup object in your schematic via the "Add Instance form".   

Click the button labeled Click to Edit Models on the Add Instance form to edit the stack, and click the Materials tab. This is where you set the material properties of conductors and dielectrics.

2. Define the stackup's material properties for the dielectric and conductor.  

Select  your layer type and specify the properties for each of your dielectrics and conductors.

3. Define the layer stack from the Choose Configuration drop-down menu.  

Select microstrip, stripline, or generate your own custom stackup.  OK the Stackup Editor form.  OK the Edit Add Instance/Edit Object Properties form.

4. Insert the transmission line in your schematic.

Below is a screenshot of the Edit Object Properties form, the Stackup Editor, and the Schematic containing the instantiated stackup.

SpectreRF rfTlineLib GUI

The rfTlineLib help pages are linked to the Add Instance/Edit Properties Help buttons of the library symbols.  So, when you click the help button on the bottom of the form, it takes you to the appropriate section of the documentation.

rfTlineLib cdns documentation help spectreRF

For more information, please see:

Article 20162518  Setting up the new Transmission Line Workshop library and rfTlineLib http://support.cadence.com/wps/mypoc/cos?uri=deeplinkmin:ViewSolution;solutionNumber=20162518

Example workshops:   Transmission Line Workshop, MMSIM 13.1, Sept 2013 (this is in the MMSIM hierarchy at $MMSIM_INST_DIR/tools.lnx86/spectre/examples/SpectreRF_workshop/rfworkshop.tar.Z.)

Documentation:   Virtuoso Spectre Circuit Simulator RF Analysis Library Reference, Product Version 13.1

Command line help.  In an xterm, type: 

spectre -h dielectric

spectre -h conductor

spectre -h stackup

spectre -h mtline


More questions? Contact Cadence Customer Support. We'd be happy to assist!


Wishing you a prosperous and joyous new year!


Best regards,



By Frank Wiedmann on January 16, 2014
The rfTlineLib brings big improvements in both performance and usability. However, there are currently a few problems remaining that users should be aware of: the fmax parameter does not work properly (CCR 1168306) and time-domain simulation results can be inaccurate (CCR 1162703).

By jyang on February 9, 2014
Does this rfTline lib support PSS (periodic steady state) analysis?

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