[sdiy] Differential 12dB/oct filter

[Tom Wiltshire]

Hi all,

I know about the differential op-amp configuration:

https://upload.wikimedia.org/wikipedia/commons/thumb/a/a2/Op-Amp_Differential_Amplifier.svg/300px-Op-Amp_Differential_Amplifier.svg.png

I've also used this with capacitors across Rf and Rg to give a 6dB roll-off above some cutoff frequency - the top of audio usually, in my case. This is the most basic differential op-amp filter.

Does anyone know a good resource for designing 12dB/oct filters with this same differential layout? Or some useful schematics?

I'm playing with the dsPIC's audio DAC again, and it has a differential output, so being able to combine the post-DAC filter and the differential amp into a single op-amp would save me an op-amp. Otherwise, it's a differential amp followed by a conventional 12dB filter.

Thanks,
Tom