Controlled-Impedance Line Designer tool sets chip-to-chip link performance

January 28, 2014 // By Graham Prophet
Agilent Technologies’s EEsof EDA's Controlled Impedance Line Designer is a software product that quickly and accurately optimises stack-up and line geometry for multigigabit-per-second chip-to-chip links, using the most relevant metric.

The product, available as an add-on to Advanced Design System 2014, uses a novel approach to design controlled impedance transmission lines. Previous tools for this task allowed only for line characteristics, such as frequency response, as the optimisation goal. In modern chip-to-chip links, this metric has become less relevant because it doesn't take holistic effects of the end-to-end link into account. Most important, the effect of the equaliser in the receiver is ignored. The metric that matters today, Agilent asserts, is the post-equalisation eye opening.

The integration of Agilent's Controlled Impedance Line Designer and the existing Channel Simulator in ADS rectifies this situation by letting engineers see a set of eye openings that result from sweeping through the pre-layout design parameters (e.g., line width).


To ensure accurate calculation of the transmission line characteristics, the software automatically employs a fast, cross-sectional (2D) electromagnetic field solver. The dielectric layers are modelled using the frequency-dependent Svensson/Djordjevic permittivity, which ensures both accuracy and delay causality. The metal layer model accounts for conductivity, skin effect, and top and bottom surface roughness.

The Controlled Impedance Line Designer also includes a provision to determine the effect of manufacturing variation on input parameters, such as thickness, on output parameters such as impedance. This new approach brings line design into the multigigabit era, Agilent says, adding that, "The whole point of the signal processing in the I/O of modern chips is to allow you to use lower-cost materials and yet still open the eye. For the first time, engineers can easily explore those interactions and trade-offs."

Agilent EEsof EDA's Advanced Design System 2014 with the Controlled Impedance Line Designer software add-on;

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