An Approach For Tuning Signal Integrity Properties Of Edge Card Connectors With Conductive Fixture In High-Speed Link Channels

Abstract

A novel edge card connector design approach with tunable signal integrity (SI) properties is proposed. The tunability is achieved through the presence or absence of a grounded conductive fixture in between the connector pin rows. The main purpose of the tunability is to take an existing connector having a certain impedance intended to work in a high-speed link channel and be able to adjust the impedance of that connector for another channel requiring a different impedance. In this paper, the fixture is designed with a thin metal layer sheet expanding beneath a connector’s pins to provide tunable capacitive coupling between the signal and the ground in order to effectively drop the connector’s impedance from 100ohm to 85ohm. Additionally, it was observed that not only was the impedance tunability achieved for the assumed connector but also improvements in crosstalk and loss potentially extending the operational bandwidth of the connector to higher frequencies. The benefits of the proposed approach are verified by simulations in both frequency-domain and time-domain. A time domain eye simulation of a typical PCIe gen4 SerDes channel designed for 85ohm impedance to work at 16 Gbps shows eye opening improvements of 10.7% and 5.2%, respectively, for the eye height and the eye width when using the tuned connector with the proposed approach.