CST – Computer Simulation Technology

ERNI ERmet zeroXT High Speed SMT Connector

This article discusses a high speed multi pair connector for modern high speed backplane designs with data transmission rates up to 10 Gbit/s 100 ohm. It uses a differential impedance SMT interface to printed circuit board with extreme shielding to achieve a minimum of crosstalk between differential signal pairs, minimum signal skew between the two contacts of a differential signal pair, and economical and easy trace routing.

One additional goal at an early stage of the design process was to give a realistic estimation of the overall system performance of a typical communication system including the newly designed connector. SPICE simulation models needed therefore to be derived from full 3D EM simulations of the key contributors to distortion and crosstalk: The ERNI Ermet zeroXT connector itself. A cut out of the PCB via pattern on both male and female sides of the connector including a short section of PCB transmission line....

Figure 1: Picture of the ERNI ERmet zeroXT High Speed Connector

The design process started with impedance simulations for the definition of the main design parameters (trace width, trace distance, distance between 2 signal pairs, distance between 2 signal wafers). According to a first draft of ERNI, AdMOS implemented a fully parametric model of a “geometrical linear” connector to analyze and optimize the impedance matching and the crosstalk in a quick and effective way.

Figure 2: Fully parametric model of linear connector

Based on the analysis described above an intermediate 3D model could be generated consisting of 3 wafers with 4 signal pairs per wafer. It was used to verify the impedance matching, the crosstalk & multiline crosstalk, the SPICE model generation and the overall system behavior performing S-parameter calculations.

Figure 3: Intermediate version of submodule

The full 3D simulation model comprised of highly complex molded plastic parts, stamped and bended contacts as well as a complete shielding structure. The SPICE simulation models were extracted from the 3D EM analysis as lumped transmission line models using the basic SPICE elements R, C, L and coupling K.

Since the connector to PCB interface is one of the most limiting factors in speed performance, numerous parametric studies have been performed to optimize this interface as well, so that all the specs could be matched.

Figure 4: Connector to PCB interface

At a final stage a test vehicle containing special de-embedding structures was designed (PCB) to verify the simulated connector behavior with measurements.

Figure 5: Picture of a specially designed test board

Figure 6: Agreement between simulation and measurement of near end crosstalk

Figure 7: Full 3D simulation model comprised of highly complex molded plastic parts, stamped and bended contacts as well as a complete shielding structure

The connector could be manufactured in one step without significant modifications and customers of ERNI could use SPICE / Touchstone models of the ERmet zeroXT connector before the first sample was available.


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