[sdiy] Forget the OTA, find me a CDTA!

[Uwe Schueler]

> Will this circuit be any good for anything but high frequency stuff?
I'm afraid you are right; modern (>90's) OTA/Gm-cell circuits have been
developed in CMOS for high speed low power LSI chips. Bad chance to see
a 14pin LMxxxx audio-CDTA ever.

> Re: Fontana bridge. Why would you need that? It seems like the purpose
> of the Fontana bridge over the usual opamp/transistor and resistor...
why an external transistor for a current source ? If you don't need it as
expo and currents are <20mA, opamp-only current sources are nice.
I often us a NIC as current source for sawtooth/triangle oscillators,
because with 1 opamp and 4 resistors you can get a current source
plus a buffered signal output !
BTW: for me the Fontana bridge looks just like a NIC variant:
https://picasaweb.google.com/Kulturgueterschuppen/Tech#5874424814629940642
Can someone explain the benefit of a 2-opamp fontana-bridge over a 1 opamp
NIC (driven by source with Ri=0 )? ( in a few words please, I have a  
higher-math-allergy ;-) )