I am somewhat confused regarding the MFB filter naming custom. In the literature, I read of the Deliyannis form, the Deliyannis-Friend form, the Rauch form, and people seemingly confuse them.

There are essentially 3 circuits (assuming a bandpass for the sake of discussion):

  • The simplest has 2 capacitors and 2 resistors
  • This can be augmented with a third resistor that is used to divide down the input signal
  • The most complex form adds a resistive divider for positive feedback to the noninverting input (often called "Q enhancement")

So, which one is which? If you know, please provide the bibliography, too.

It also crossed my mind that it might have something to do with capacitor choice, too. Both capacitors are usually chosen to have equal capacitance, "for convenience". Are there different names for the circuit with equal and nonequal capacitor values?

  • \$\begingroup\$ You just want to know how names are used in the literature? That's it? \$\endgroup\$ May 7 at 19:55
  • \$\begingroup\$ @periblepsis That's it, yes. What's the point of naming things when the names are being used randomly? \$\endgroup\$
    – sh-
    May 8 at 11:20
  • \$\begingroup\$ Nature has natural demarcations. For example, the difference between a planet and a dwarf planet is about 5 orders of magnitude of a gap where nothing we know about exists. So there is meaning there that nature shows us. Humans often just make up words with arbitrary distinctions and less than a factor of 2 between them if lucky. Often, overlapping and confusing. We aren't logical beings. Unlike nature, which is profoundly consistent. If you want to know what people use in the literature then you will need to study the literature. Humans aren't rational. So just study the usage, I guess. \$\endgroup\$ May 8 at 11:57
  • \$\begingroup\$ I tend to avoid such debates like the plague. If someone can show me how nature makes a clear demarcation, then I'll listen to assigned words. Otherwise, I tend to avoid listening. I don't want to be confused by assigned words without any clear demarcations shown to us by nature. Avoiding arbitrary human divisions helps to keep me thinking more clearly about a subject and avoiding confusion. That's just me, though. You are free to follow your own path. \$\endgroup\$ May 8 at 12:00
  • \$\begingroup\$ @periblepsis I didn't expect nature to come into it. All those filters are human inventions, and so are their names. Giving names to the individual variants, I suppose, is meant to identify the variants unambiguously. Confusing them with each other undoes that, so that using the names becomes entirely unhelpful. Maybe that's what the situation is, and I should just give up on the names altogether. \$\endgroup\$
    – sh-
    May 8 at 13:09


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