Okay--
I've racked my brain trying to figure this one out. I'm trying to figure out how to analyse and design filters of this topology. I understand how the "Twin-T" part of it works, but I can't figure out the interaction between Co and Ra/Rb. And I can't find a text that explains it. I'm getting the results out of a filter design tool, and it doesn't explain how it derives the results.
This is being used as a building block for a higher-order active Cauer-Elliptic filter.
Fc = 747.9366
Q = 0.7164
Fnotch=7557.0414
*Ra=1k
Rb=44.5k
R=2.11k
*C=10n
Co=505n
* = Values I provided to the calculator.
R and C work for the correct notch frequency in a Twin-T topology.
Any help that the experts out there can provide would be appreciated. There is a similar high-pass topology with Co replaced by a resistor, but I haven't even started playing with that.
--Greg
I've racked my brain trying to figure this one out. I'm trying to figure out how to analyse and design filters of this topology. I understand how the "Twin-T" part of it works, but I can't figure out the interaction between Co and Ra/Rb. And I can't find a text that explains it. I'm getting the results out of a filter design tool, and it doesn't explain how it derives the results.
This is being used as a building block for a higher-order active Cauer-Elliptic filter.
Fc = 747.9366
Q = 0.7164
Fnotch=7557.0414
*Ra=1k
Rb=44.5k
R=2.11k
*C=10n
Co=505n
* = Values I provided to the calculator.
R and C work for the correct notch frequency in a Twin-T topology.
Any help that the experts out there can provide would be appreciated. There is a similar high-pass topology with Co replaced by a resistor, but I haven't even started playing with that.
--Greg
Attachments
The more usual way of doing a T filter is shown here:
http://focus.ti.com/lit/an/slyt235/slyt235.pdf
Not sure why you are interested in Co, are you trying to compensate for the input capacitance of the op-amp? It will be small enough to be ignored in most cases.
http://focus.ti.com/lit/an/slyt235/slyt235.pdf
Not sure why you are interested in Co, are you trying to compensate for the input capacitance of the op-amp? It will be small enough to be ignored in most cases.
consort_ee_um--
Thanks for the link to the App. Note. I found that earlier in my search. But I'm not looking for *just* a notch filter. This topology is a lowpass filter with notch. The circuit I've shown above provides the frequency response attached. Co and Ra/Rb interact to provide the lowpass functionality (everything else is just your basic Twin-T notch), but I can't figure out how they interact and how to derive the values.
--Greg
Thanks for the link to the App. Note. I found that earlier in my search. But I'm not looking for *just* a notch filter. This topology is a lowpass filter with notch. The circuit I've shown above provides the frequency response attached. Co and Ra/Rb interact to provide the lowpass functionality (everything else is just your basic Twin-T notch), but I can't figure out how they interact and how to derive the values.
--Greg
Attachments
Hi GMikol,
I suggest you have a look there :
http://www.diyaudio.com/forums/showthread.php?s=&threadid=6655&highlight=
there is a reference to Bainter's notch filter, I can send you his paper. Just email me.
I suggest you have a look there :
http://www.diyaudio.com/forums/showthread.php?s=&threadid=6655&highlight=
there is a reference to Bainter's notch filter, I can send you his paper. Just email me.
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