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Take the Guesswork out of Discrete Circuit Design (.PDF Download)

Nov. 28, 2018
Take the Guesswork out of Discrete Circuit Design (.PDF Download)

Designing circuits with discrete resistors, inductors, and capacitors can be a tricky problem for RF design engineers for several reasons. For example, consider the scenario in which a filter must be designed with discrete inductors and capacitors. In these situations, simple software tools are available that can automatically calculate the inductor and capacitor values. The software generates these values based on user-specified parameters, resulting in a filter design with an optimal frequency response.

However, these types of software tools also come with limitations. For one, they only calculate ideal inductor and capacitor values. Since real-world discrete inductors and capacitors are not ideal components, their actual performance does not entirely match the theoretical performance of ideal parts.

Specifically, real-world discrete inductors and capacitors contain parasitics that affect their performance. That means that the performance of a real filter designed with these components can differ significantly from the calculated performance of a theoretical filter designed with ideal parts of the same value.

The presence of parasitics is not the only factor that must be taken into account. With a software tool, a seemingly infinite amount of component values can be calculated to satisfy any given criteria. However, designers must keep in mind that vendors only manufacture inductors and capacitors with a finite number of values. Thus, it may not even be possible to obtain inductors and capacitors with the exact values generated by a software program. While one could simply find real parts with the closest values, this factor can nonetheless have an impact.