![]() Let’s start with a simple, but often misunderstood, aspect of a specific and simple kind of filter: delay lines. As always, I will use only engineer-oriented explanations, with circuits and simulations, rather than mathematics. Now, four years later, isn’t it a good time to dig a little more into that topic? What is this “group delay” about? Why would a flat group delay help? In which designs is it a benefit? In this article I will do my best to give you some information about these topics. Let’s keep the subject for another article.” That would bring us a little too far here, but these characteristics preserve the shape of the filtered signals. A Bessel filter is not very good both in terms of flatness and attenuation, however it has a key advantage in the time domain: Its so-called group delay is nearly flat. “The last common variant, Bessel filters, is a little more complex to understand. I also briefly introduced the so-called Bessel filter. In that article, I presented the basics of passive and active filters, and talked about standard filter responses, such as those of Butterworth, Chebyshev and others. Long-time readers may remember an article I wrote on analog filters some years ago: “Analog Filters for Dummies” ( Circuit Cellar 307, February 2016). That day has now come, as Robert digs into group delay and why it’s significant. Four years ago, Robert wrote a Circuit Cellar article exploring analog filters, but he concluded that article with a promise to someday discuss the idea of group delay in filtering.
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