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Method for impedance matching for high-speed differential signaling

IP.com Disclosure Number: IPCOM000009283D
Publication Date: 2002-Aug-14
Document File: 3 page(s) / 145K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for impedance matching for high-speed differential signaling. Benefits include improved signal quality and improved support for high-speed trace routing.

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Method for impedance matching for high-speed differential signaling

Disclosed is a method for impedance matching for high-speed differential signaling. Benefits include improved signal quality and improved support for high-speed trace routing.

Background

              Differential signaling trace pair impedance must match the impedance of an external device (see Figure 1). For example, an industry-standard differential coax cable as differential impedance equal to 100 Ohm. The space between the traces (distance S) must be large enough to match the impedance. Although this requirement can be met, differential routing must occupy a larger routing area. Moreover, the large space between two differential traces degrades the coupling (see Figure 2) and damages the signal integrity. This problem is exacerbated as products require more I/O traces and higher signal integrity.

General description

              The disclosed method handles the impedance matching problem for differential signaling by scratching off a metal segment of the ground plane under the traces (see Figure 3). This approach decreases the self-capacitance for both traces while the coupling between traces remains approximately the same. The differential impedance can be matched to a required number (for example, 100 Ohm) without enlarging the space between traces, occupying silicon surface area.

              The disclosed routing design enables more coupling than the conventional design (see Figures 4 and 2) while both cases...