3

Inductance

Inductance is a very important line and device parameter for predicting Signal Integrity (SI) and Radiated Emission (RE). In this chapter, the self and mutual inductances of coupled loops are theoretically introduced considering two generic loops, and the associated equivalent circuits are derived. The L matrix concept for two coupled wires having a reference return conductor is provided as background to build an inductance matrix L for n-multiconductor transmission lines. As an example, closed-form expressions for L matrix calculation for round wires are given. The dependence of inductance on frequency is discussed.

The concept of partial inductance as a consequence of the segmentation of a loop is introduced in Section 3.2. Partial inductance is very useful for building up lumped-circuit models of electrically short parts of a PCB, such as the package in IC devices, vias, and connectors, in the case of SI predictions, and of a PCB with a finite ground plane in the case of RE predictions. Simple closed-form expressions of self and mutual partial inductance for round and rectangular conductors are provided. An example of an equivalent circuit with partial inductances is described for the case of a decoupling capacitor and a switching device located in a multilayer PCB.

The definitions of differential mode and common mode inductances are outlined at the end of the chapter. These definitions are very useful for crosstalk modeling, differential signaling, and filtering ...

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