Talk:Active filter

message: It seems to me that the diagram shown here is less an active filter than an ac coupled inverting amplifier because the filter component is inactive.  That is, it doesn't rely on the amplifier for its function in any way except for the virtual ground the amplifier provides.  Its filtering function could be duplicated by a passive RC filter except for the buffering effect of the amplifier.  The more common active filter would be in the form of a Sallen-Key filter (non-inverting) or a multiple feedback filter (inverting) in which the amplifier provides positive feedback to shape the filter's response and make it roll off more quickly into the stop-band.  If I can figure out how to upload a diagram, I'll substitute a better one. Anoneditor 23:01, 11 July 2006 (UTC)
replies: text: But it's also an impedance buffer, which is a defining characteristic of active filters. — Omegatron 23:21, 12 July 2006 (UTC)
replies: text:  Maybe, but the same result (minus the signal inversion) would occur using a voltage follower after a simple RC filter, and that combination would hardly be characterized as an active filter.  I think the defining characteristic of an active filter is the use of amplifier feedback to control the shape of the filter's response.  To me, the buffering action is more ancillary (though certainly useful) than defining.  In any event, don't you agree that the original figure wasn't ideal for the purpose of showing an example of an active filter? Anoneditor 05:41, 13 July 2006 (UTC)

text: You seem to forget the R1 resistor which is connected to the output ... it is a feedback. Majorkell 15:33, 24 August 2007 (UTC)
replies: text: No, I haven't forgotten it.  The discussion with Omegatron was over the diagram that pre-existed the current one, i.e., the one that existed prior to July 11, 2006.Anoneditor 20:14, 24 August 2007 (UTC)
thread_title:  Comments 

message: There is the beginnings of showing the "family tree" (taxonomy?) of filter types on the main filters page, but (quite rightly) it doesn't go into details of all the types of active filter available. I think something should be here; a diagram of some sort, but there are all sorts of ways to look at them, e.g. order of filter, number of amplifiers, high/low/band-pass etc, as well as an alphabetical list of names (yet textbooks are far from consistent in their use of names, and drilling down to see the circuits in such a list is a slow way of identifying a circuit you have in front of you).  Also, there are details like mathematical treatment - zero/pole approaches - should that be the way to classify them (e.g. some books define second order in terms of the highest power of "s") - yet isn't that level of theory too far above the reading level this is pitched at? To go that way (which would be helpful to some readers) there would have to be lots of stuff added to wiki, like an easy explanation of all-pole for example.
Maitchy (talk) 07:11, 4 August 2009 (UTC)
thread_title:  Categories of filter 

message: A type of active filter that I've come across, is the leapfrog filter. It doesn't seem to be mentioned on Wikipedia yet. It is similar to the state variable filter, I think. It's probably worth both a mention on this page, and a separate article. --HelgeStenstrom (talk) 08:59, 26 October 2010 (UTC)
replies: text: @Helge, Do you have a link to something? That would be more helpful, as you have noticed nobody have picked up this thread in the last 9 years. Jahibadkaret (talk) 17:35, 26 April 2019 (UTC)
replies: text: Leapfrog filter Constant314 (talk) 21:43, 26 April 2019 (UTC)
thread_title:  Leapfrog filters 

message: If the Twin T filter is a fully passive filter, why is it listed in this article which is about active filters?
ICE77 (talk) 17:29, 11 May 2011 (UTC)
replies: text: I took it out. Dicklyon (talk) 20:38, 11 May 2011 (UTC)
thread_title:  Twin T filter 

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thread_title:  External links modified