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Differential or normal mode component mounting for signal integrity and low emissions

IP.com Disclosure Number: IPCOM000201798D
Publication Date: 2010-Nov-23
Document File: 4 page(s) / 229K

Publishing Venue

The IP.com Prior Art Database

Abstract

A surface-mount (SMT) component is described for usage on printed circuit boards. This component addresses a problem where a high-speed signal net is brought from an internal layer to the surface to go through a component (e.g., resistor or capacitor). In this process, the signal looses its reference creating an impedance discontinuity and possible radiated emission source. To remedy, a component is proposed which provides a connection to both the signal net(s) and their reference planes, allowing the reference to be maintained through the component package. Additionally, a component is proposed which provides this referencing continuity as well as a "socket" to allow a typical 0402-sized surface-mount component to be placed inside the proposed component. This allows for unlimited flexibility with different component types and values while maintaining the signal referencing..

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Page 01 of 4

    Improvement is needed in both normal and common mode matches for high-speed signal integrity where the current is brought to the surface to enter a surface-mount component and then returned to the interior of the board. This mismatch, although slight at medium frequencies, becomes significant as the signal voltage levels decrease and the rising edges decrease.

    To address this signal reference problem, the component described here is placed on the surface where the desired component goes. The signals are brought up through the package routing to either a socket, where a discrete SMT is placed, or to a component built into the package. In addition to the signal nets, the primary reference plane is also routed up through the package, allowing for greater control over the impedance seen by the signal nets.

    The socket-equipped version accepts either (2) single-ended 0402-sized components (for a differential signal), or (1) single 0805-sized component. Since the reference plane is brought through the component, the signal paths may continue to follow the reference plane even though it's transitioned from one side of the circuit board to the other.

    The package may take the form of a fine-pitch leaded component or, most optimally, a package with a ball grid array (BGA) on the underside. Such configuration would minimize the package's equivalent series inductance (ESL).

    Figures 1 and 2 show the existing mounting method for a simple (not differential) component where the origin of the mismatch can be clearly seen.

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    Then, Figures 3 through 12 show the various configurations that devise the embodiments of the invention.

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