MatthewF
Well-known member
Hi there, I'm hoping that someone can help me clarify some points with regards to noise and interfacing, as I'm starting to get a little confused (maybe trying to think too hard!)
I was recently reading the data sheet for an INA134 instrumentation amp and considering using it to realise a balanced line-level input. I noticed that it has a noise voltage of 52nV/rootHz (7.35uV with 20kHz bandwidth).
Assuming a 200ohm source impedance (about 1.8nV/rootHz) this would result in a noise figure of 29.5dB.
This sounds terrible, but I assume the INA134 is acceptable for a line level input due to the higher signal level? If this is the case, does that imply that the calculation of a noise figure is only relevant to high gain mic amps etc. (where input signal level is very low)?
This leads me to ask what measurement is suitable for gauging the noise of a line level input. It is clearly relative to signal level. I've seen spec sheets citing THD+Noise as a percentage. Does this refer to the percentage the of total power which is contained within noise and distortion, at a given signal level?
If this given signal level were +4dBu, that would imply a signal voltage of 1.23vRMS. How would this 1.23v signal level and 7.35uV voltage noise be compiled into a useful parameter with which to compare designs?
Thanks for any help,
Matthew
I was recently reading the data sheet for an INA134 instrumentation amp and considering using it to realise a balanced line-level input. I noticed that it has a noise voltage of 52nV/rootHz (7.35uV with 20kHz bandwidth).
Assuming a 200ohm source impedance (about 1.8nV/rootHz) this would result in a noise figure of 29.5dB.
This sounds terrible, but I assume the INA134 is acceptable for a line level input due to the higher signal level? If this is the case, does that imply that the calculation of a noise figure is only relevant to high gain mic amps etc. (where input signal level is very low)?
This leads me to ask what measurement is suitable for gauging the noise of a line level input. It is clearly relative to signal level. I've seen spec sheets citing THD+Noise as a percentage. Does this refer to the percentage the of total power which is contained within noise and distortion, at a given signal level?
If this given signal level were +4dBu, that would imply a signal voltage of 1.23vRMS. How would this 1.23v signal level and 7.35uV voltage noise be compiled into a useful parameter with which to compare designs?
Thanks for any help,
Matthew