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Current feedback Op-Amp

I have an application for a fairly high power op-amp (50MA - 24Vp-p into 300ohms) at audio frequencies. For several reasons, likely some not very good, I selected the AD810 for a test. After doing some more research I'm having second thoughts about a current feedback amp in this application (Howland current source), though the simulation looks good. Specifically I'm concerned about the zero input impedance at the inverting input. I still have (a little) time to change it to a voltage feedback amp, but would rather not for this test. Not having been an analog type for years (and having never used a current feedback amp), I thought I'd get the opinion here. Thanks.

--
Keith
Reply to
krw
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Maybe post your schematic? Vagueness gets you garbage solutions ;-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

I came across this, earlier today

formatting link
probably overkill though

martin

Reply to
Martin Griffith

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.

--
Keith
Reply to
krw

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).

--
Keith
Reply to
krw

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

Howja like that +10dB peaking ?:-)

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
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.

--
Keith
Reply to
krw

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

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

Understood. Five orders of magnitude is a lot though.

--
Keith
Reply to
krw

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

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
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

Reply to
Phil Hobbs

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

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

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

...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
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).

--
Keith
Reply to
krw

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

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
 I love to cook with wine     Sometimes I even put it in the food
Reply to
Jim Thompson

24Vp-p

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.

--
Keith
Reply to
krw

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