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Old 28th June 2011, 02:37 PM   #11
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Oon,
We are discussing resitance loads, not voltage. The + and - outputs should have the same resistance across them to ground.
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Old 30th June 2011, 10:54 AM   #12
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The chip is a single supply 5v, so the voltage at the output should be loaded to 2.5V, vref. Since the ideal load is 0ohm or input of an IV converter, I think it would be to just short it to vref..

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Old 30th June 2011, 11:58 AM   #13
Previously: Kuei Yang Wang
 
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Hi,

Quote:
Originally Posted by oon_the_kid View Post
The chip is a single supply 5v, so the voltage at the output should be loaded to 2.5V, vref. Since the ideal load is 0ohm or input of an IV converter, I think it would be to just short it to vref..
Okay, so you worked it out. When you asked "what is loading" I decided I had started something I was unwilling to finish.

Some comments, if you are going to use Op-Amp I/V anyway, use the OPA1632. It has many great advantages in such an application, like balanced inputs and outputs, so it makes a balanced I/V converter, very low noise, folded cascode singe gain stage architecture and very good output buffers. So you end up with a system having two equal but opposite polarity outputs so you can easily take a single ended output.

Otherwise, remember that an Op-Amp I/V circuits input only looks like a short at DC and very low frequencies...

If you where (for arguments sake) using tubes or maybe discrete J-Fets and wanted to avoid the balanced to se conversion, then loading both DAC outputs with identical I/V conversion RC (or whatever) combinations and using the signal from only one would be the choice, however.

I hope the above helps make your choice.

Ciao T
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Old 4th July 2011, 12:34 AM   #14
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Hey thanks for all the clarification and tips. Really appreciate it. Very likely, I will do nelson pass D1 IV stage.
But the tip on the opamp is really useful.

Oon
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Old 4th July 2011, 02:09 AM   #15
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Hi,

Quote:
Originally Posted by oon_the_kid View Post
Hey thanks for all the clarification and tips. Really appreciate it. Very likely, I will do nelson pass D1 IV stage.
If you use this single ended, it is important to remember that it's input impedance is not zero.

Ciao T
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