[sdiy] Low Cost Comb Filter Methods

Neil Johnson neil.johnson71 at gmail.com
Fri Jun 15 11:54:58 CEST 2018


Andrew Simper wrote:
> Thanks for pointing that out, I didn't take a loop at the part number and
> there was no regular symbol of the current arrow at the inputs like there is
> meant to be on the op-amp inputs to differential it from a regular op-amp as
> shown in figure 4 part (b) here:
> http://www.ti.com/lit/an/snoa653/snoa653.pdf .

That paper is a bit vintage, and smells of Bob Pease.

The LM3900 datasheet is a little bit more contemporary:

> Can you please give me the theory of operation of an ideal "Norton op-amp"?
> Once I have those equations I can add this as a new device to my solver and
> re-generate the code. As an example the defining equations for an ideal
> op-amp are here:
> http://qucs.sourceforge.net/tech/node67.html

Yeah, I tend to think of the ideal op-amp as a little white lie, like
Father Christmas and the Tooth Fairy, only suitable for 1st year


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