How does Attenuation help with noise performance

[KD494]

I've just read that attenuating a signal can help with noise performance. I understand that reducing signal level would decrease the power of the noise but wouldn't the SNR stay the same? On top of that, in practical application wouldn't you be adding more noise through whatever passive or active components you use to accomplish the attenuation? I must be missing something because I've seen a circuit where the signal is attenuated with a resistive ladder and then immediately gained up again.:thinker:

Thanks.

 

[kemiyun]

Can you share the source? Because usually attenuation does terrible things to noise, and usually preferred when it's unavoidable in analog design. In RF they're more common but still not a good thing because Friis rule. But this is not to say some special cases don't exist.

The thing they mentioned might be the case where all the signal chain was getting more power than it could handle (close to IP3 point), where it would do wonders to your distortion performance. Or the same can be said about input of any analog circuitry.

 

[KlausST]

Hi,

I can´t imagine a situation where attenuation of the signal gives an improvement in SNR.

But it can improve THD. And often one find SINAD, where noise as well as distortion is calculated. SINAD could be improved by attenuation of the signal.

Klaus