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[SOLVED] Relation between SNR and gain in a OpAmp

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flote21

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Hi guys,

I am wondering how could affect to the SNR of an OpAmp when the Gain is multiplied by 2.

Thanks in advance.
 

Hi,

it surely depends on the circuit and the source of noise.

If you just talk about OPAMP input voltage noise....and refer it to the output voltage range...
Then noise at the output will be about doubled, but output voltage range stays the same.

--> SNR will decrease by about 6dB.

Klaus
 
Hi Klaus, thanks for your quick answer.

Just one question more comes to my mind.

SNR(dB)=20log(Vout/Noise)

If the gains is the double, should not be double also Vout? Why do you stimate only the noise is x 2?

Thanks in advance
 

Hi,

Let´s assume an OPAMP with 10uV RMS input voltage noise.
And a +/-15V supply.

Maybe the max output voltage is +/-12Vpp.
This is about 8.5V RMS

at a (noise) gain of 10...
you will see about 100uV noise at the output --> 98.6dB SNR

****
Now double the (noise) gain by 2 and get 20.

You may expect about 200uV RMS noise at the output.
But the (usable) output voltage range will still be 8.5V RMS --> 92.6db SNR


Klaus
 
Got it!!! Thank you so much KlausST!!!

Regards.

Hi,

Let´s assume an OPAMP with 10uV RMS input voltage noise.
And a +/-15V supply.

Maybe the max output voltage is +/-12Vpp.
This is about 8.5V RMS

at a (noise) gain of 10...
you will see about 100uV noise at the output --> 98.6dB SNR

****
Now double the (noise) gain by 2 and get 20.

You may expect about 200uV RMS noise at the output.
But the (usable) output voltage range will still be 8.5V RMS --> 92.6db SNR


Klaus
 

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