Coilcraft

Many consumer products communicate over broadband networks. From television to fiber transmission networks, the bandwidth of data communication is increasing, and the integrity of RF signals has become a major concern. This paper demonstrates how inductors are used for RF isolation in circuits ranging from relatively narrow band applications like portable devices up to broadband networks for data distribution.

RF inductor selection involves these key parameters: mounting (surface mount or through-hole), inductance value, current rating, DC resistance (DCR), self-resonant frequency (SRF), Q factor, and temperature rating. While small size is typically desired, the laws of physics limit how small an inductor can be for a given application.

Understanding the meaning of S-parameters, how they are measured, and their limitations can lead to more meaningful simulations of RF- and microwave-frequency inductors, chokes, wideband RF transformers, and high-speed common mode chokes. This document describes how S-parameters are generated and how to best apply them to your simulations.

There is more to selecting an inductor than the nominal inductance value. To ensure your choice will perform in your application, you need to give careful consideration to inductance tolerance, current ratings, DCR, operating temperature and efficiency under specific conditions. This paper provides students and anyone new to inductors with an overview of the key performance ratings they will need to understand when specifying RF and Power Inductors.

In broadband bias applications, most inductors do not cover enough impedance bandwidth. Bandwidth can be increased by putting three or four inductors in series, but DC losses and filter complexity increase. Instead, a broadband bias choke provides wide bandwidth in a single inductor package.

RF inductor selection involves a number of key parameters including, mounting (surface mount or through-hole), inductance value, current rating, DC resistance (DCR), self-resonant frequency (SRF), Q factor, and temperature rating. While small size is typically desired, the laws of physics limit how small an inductor can be for a given application. Inductance value and current rating are the chief determinants of size. Once they have been calculated, other parameters can be optimized.

Impedance mismatch in a circuit results in energy be¬ing reflected back to the source, reducing the amount of power available to the load and possibly causing damage to the power source. Matching the output impedance of the power source to the input impedance of an electrical load maximizes power transfer from source to load.

High speed data interfaces like USB, HDBaseT™, HDMI, DVI, and DisplayPort require careful consideration to ensure reliable communication that is free of disruptive EMI. Of the many tools at the designer’s disposal like trace routing, termination and component placement, the common mode filter choke remains one of the most powerful. This application note discusses the benefits of using common mode chokes and reviews the performance characteristics associated with their proper application.