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Old 14th May 2004, 07:06 PM   #1
zahlm is offline zahlm  Spain
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Question op amp distortion

there is a thing I don't understand while I look the datasheets
why do the non inverting configurations have more THD distortion than inverting config?

Thank, Zahlm
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Old 15th May 2004, 06:46 AM   #2
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What happens with the input in non-inverting mode? Both + and - inputs are lifted up and down in phase with the music. This creates distortion. It has to do with "common mode rejection ratio".

In inverting mode the inputs are rather still, they are very close to ground all the time!
/Per-Anders (my first name) or P-A as my friends call me
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Old 15th May 2004, 12:09 PM   #3
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In inverting mode (if the input impedance of the opamp were infinite) the signal at the junction of the input resistor and the feedback resistor (the summing junction) is a *perfect* representation of the difference between the input signal and the output signal, and it is this signal that is fed into the opamp.

In the non-inverting method, the feedback signal is fed into the opamp (-) input and generally passes through at least one emitter follower before it gets to the (internal) summing junction. This means that the feedback signal is *not* a perfect representation of the output signal but it has been corrupted somewhat by passing through this emitter follower and whatever else it might find on it's way.

Something worthwhile for the GainClone crowd to consider too.
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Old 15th May 2004, 07:45 PM   #4
zahlm is offline zahlm  Spain
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Thank you very much, that's what I need to know

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