• Conference
    Jan 30-Feb 1, 2018
  • Expo
    Jan 31-Feb 1, 2018
  • Santa Clara Convention
    | Santa Clara, CA

DesignCon 2018 Schedule Builder

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A Causal Conductor Roughness Model and its Effect on Transmission Line Characteristics

Location: Ballroom E
Pass Types: 2-Day Pass, All Access Pass, Alumni All Access Pass - Get your pass now!
Track: 14. Modeling and Analysis of Interconnects
Audience Level: Intermediate
Format: 45-Minute Technical Session
Audience Level: Intermediate
Recording: TBD

In the GB/s regime, accurate modeling of insertion loss and phase delay is a precursor to successful high-speed serial link designs. We propose a causal (physically meaningful) form of the Hammerstad and Cannonball-Huray metal roughness frequency dependent complex correction factor. Compared to the widely used, non-causal form, it considerably increases the inductive component of internal metal impedance. Transmission lines simulated with a causal version demonstrate increased phase delay, and characteristic impedance. By obtaining the dielectric and roughness parameters, solely from manufacturers' data sheets, we validate the model through a detailed case study to test the model`s accuracy.


Metal roughness models used in simulators are non-causal and cause inaccurate simulation results. We derive and explore causal version of Hammerstad, Huray and Cannonball-Huray (C-H) roughness models. We show that causal roughness model increases internal metal's inductance. Consequently, transmission line model has larger phase delay and characteristic impedance. By accepting roughness parameters solely from manufacturers' data sheets, and using causal version of Cannon-ball-Huray model, a case study using FR408HR/RTF show excellent simulation correlation to 50GHz.

Intended Audience

The target audience is anyone who is involved in the design and fabrication of high-speed circuit cards and/or backplanes, and needs to be able to accurately estimate PCB transmission line losses and phase delay in the GB/s regime from first principles. A basic understanding of transmission line theory, dielectric and metal properties, S-parameters, PCB stackup and fabrication would be useful.