[sdiy] Why do we need the buffers? - gm-C filter question

[JH.]

>> Your BJT OTA inputs aren't really hi Z in the same sense that opamp 
>> inputs are. Basically the input current is a function of the input
>
>It makes me wonder how the situation changes if we started building OTAs 
>out of CMOS instead... 

Even with BJTs, you can design OTA filters without buffers. The Zin of each
stage changes with Iabc, so you have a tracking input impedance. 
You just have to put Zin into the equatation, and you can
design a polygon filter just as well as with buffers.

No, I think the main drawback is parasitic Cs.

JH.