[sdiy] Low Cost Comb Filter Methods

[Andrew Simper]

Hi Neil,

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 .

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

Thanks!

Andy

On Fri, 15 Jun 2018 at 00:26, Neil Johnson <neil.johnson71 at gmail.com> wrote:

> Hi,
>
> Andy wrote:
> >> If anyone is interested in the linear case then here are the equations
> to solve the circuit:
> >> https://cytomic.com/files/dsp/comb-filter-resonator-equations.pdf
> >>
> >> and here is an implementation in python generator by my circuit solver:
> >> https://cytomic.com/files/dsp/comb-filter-resonator.py
> >>
> >> and a plot of the filtering of a sawtooth given one set of component
> values:
> >> https://cytomic.com/files/dsp/comb-filter-resonator.png
>
> Brian wrote:
> > There’s one error in your reproduction of the schematic, though. rp is
> not supposed to be grounded, but should be connected to the +V supply. How
> much does that change the equations? It should reverse the current through
> the resistor, at the very least.
>
> And also note that the op-amp used is a Norton op-amp, so it draws
> current on its inputs.  That will change the equations.
>
> Neil
> --
> http://www.njohnson.co.uk
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20180615/ccf912dd/attachment.htm>