Current feedback Op-Amp

Maybe post your schematic? Vagueness gets you garbage solutions ;-)

...Jim Thompson

I came across this, earlier today

martin

I don't have the exact schematic here, other than it's a classical Howland current source driving two loads (a transmission line and an impedance matching leg) connected as a bridged trans hybrid. My concern is with the current feedback amplifier in the Howland current source.

I haven't thought through the ramifications of the CF amp's input characteristics WRT a VF amp. I'm having a bit of trouble with the whole concept. I guess next weeks job is wrapping my arms around CFAs.

Kinda neat. I'll file it away, but I don't see how it's going to help me here and it's kinda expensive (almost $5).

I didn't realize it was April 1...

Howja like that +10dB peaking ?:-)

...Jim Thompson

Didn't think it was that funny, though I'm out of my normal water here.

I ignored it because the intended use is almost a full page left of the "peak". The application is audio, and not for phoolz.

That peak portends instability in the feedback loop(s).

...Jim Thompson

Understood. Five orders of magnitude is a lot though.

Only if you configure the feedback loop to guarantee that the peaking occurs _well_ after the closed-loop response crosses zero dB.

...Jim Thompson

Nice that they finally realized they needed to resurrect the LH0033, though...the specs are quite similar apart from the ugly peak.

Cheers,

Phil Hobbs

Yep. And truly an ugly architecture. Wonder why they didn't do it in BiCMOS?

...Jim Thompson

Answering my own question... probably because of the voltages.

...Jim Thompson

Sure, but five decades is a lot of space to roll the gain off to below 1. A single pole squishes 100dB in that space. ;-) The nominal gain of this thing is only 1 (though it is in the feedback path).

It's the overall loop gain that matters, so you simply need to add this "unity gain" (in dB's) to the that of the LME49710 or whatever it is you're using. Loop phase is what will get you ;-)

...Jim Thompson

Sure, that's what I meant by it being in the feedback path. Does anyone use output stages for a lot of voltage gain? Sounds dangerous.

Which, to me is why that hump has "Danger Will Robinson" written all over it, but again, it's 5 decades away for where I care.