[sdiy] Operational Transconductance Amplifiers

[René Schmitz]

Hi Walker,

maybe this could help you:

http://www.uni-bonn.de/~uzs159/ota3080.html

Cheers,
  René

Walker Shurlds schrieb:
> Recent post called Source for 3080's reminded me, so I thought I'd ask.
> 
> As a noob, albeit one with circuit analysis skills, I've decided to
> analyze every part of the ASM-1 until I grok it before building
> anything serious. There are a few minor things I don't quite get yet
> (the capacitor between the negative input and the output of the expo
> converter op-amp, for instance) but I'll figure it out in time.
> 
> But when I flipped the page from the VCO to the VCF I said "WHAT THE
> HELL IS THAT!?".  Eventually figured out that it's one of these OTA
> things.
> 
> Anyway, I'm having difficulty figuring out how they work.  Wikipedia
> gave me an equation for the open-loop gain (Iout = Vdiff*gm), but that
> doesn't tell me at all what Iabc or Ibias are for at all, and doesn't
> help much with solving a circuit. Based on the ASM-1 VCF schematic, Iabc
> is the part that actually does the "VC" in "VCF"!
> 
> So, yeah.  How exactly do these things work and/or does anyone know of
> a good website/book that explains them thoroughly?
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