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[SOLVED] noise figure when parallelling op amp inputs

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Colon

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Ok,

So I am designing a circuit that will split an input 8/16 ways and I have to watch my noise figure. I have modelled various op amp configurations and found my measured noise is within a dB of my calculated noise figure. good enough for me for now :)

One of my possible approaches to splitting my input is just to feed 8/16 op amp inputs simultaneously. My question is what happens to the noise figure for each of the split outputs? The noise figure is calculated as input referred, and based obviously on the current and voltage noise on the op amp inputs. Does this mean that the noise contributions from the other parallel op amps will add at the common input feed point, and then get amplified by each channel, thus making the noise for each much worse. Or, is the input referral and use of the input voltage and current noise merely a model, and the noise actually only appears at the output, therefore meaning there will be a negligable effect on noise figure?

Obviously I could set this up and measure it, but this would take me some time from where I am currently at and I also want to understand the mechanism behind it, whatever the answer.

Thanks
James
 

Colon

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Well, if anyone wants to know. I did a test with 4 op amps and their input connected in parallel, outputs separate. I measured no noticeable increase in noise figure when this was done. So, for now, my conclusion is that the voltage noise at least (which is the main contributing factor in my setup, not the current noise) does not appear at the input of the op amp itself. I can now merrily proceed with my design :)
 

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