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Method for highly isolated power planes and/or ground planes using stepped impedance transmission line filters

IP.com Disclosure Number: IPCOM000007714D
Publication Date: 2002-Apr-16

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a method for highly isolated power planes and/or ground planes using stepped impedance transmission line filters. Benefits include improved performance and improved signal quality.

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Method for highly isolated power planes and/or ground planes using stepped impedance transmission line filters

Disclosed is a method for highly isolated power planes and/or ground planes using stepped impedance transmission line filters. Benefits include improved performance and improved signal quality.

Background

              As system bandwidth increases, power and ground distribution for high-speed systems becomes critical. In particular, minimizing noise interference between power planes and ground planes becomes crucial for achieving maximum system bandwidth.

              Conventionally, interference minimization between power planes is achieved by using decoupling capacitors and/or choke coils. They are very efficient methods for improving the power isolation. However, the impedance of a decoupling capacitor increases quickly after series resonance (see Figure 1). That is, as frequency increases, the performance of a decoupling capacitor deteriorates. As a result, the noise interference between power planes increases. High-frequency isolation between power planes is essential for maximizing system bandwidth. In addition, isolation between ground planes is required for electrostatic discharge (ESD) protection and ground bounce noise interference minimization.

              The conventional use of a conducting neck or choke coil is insufficient for high frequency isolation between the planes because of the poor performance in rejecting high-frequency noise (see Figure 2).

General description

              The disclosed method uses a stepped impedance filter (SIF) scheme to reduce noise interference between the power planes and/or ground planes for signal groups on motherboards, CPU/chipset packages, and GHz CPU chips. The method applies to the various types of signals, including:

§         Analog

§         Digital

§         Radio Frequency (RF)

§         Mixed

              The components of the method are as follows:

§         Low impedance scheme such as power/ground planes with or without capacitor

§         High impedance scheme such as narrow meandered transmission line or spiral inductor with or without reference plane (Split reference plane recommended)

§         Low impedance scheme such as power/ground planes with or without capacitor

Advantages

                  The advantages of the disclosed method include the following:

§         High isolation, particularly for high frequency noise, between ground planes and power planes for ESD protection and noise interference minimization

§         Design flexibility by changing the cutoff frequency and the attenuation of th...