#### ElecDesigner

##### Member level 5

Hi,

I am designing a preamp for a type of transducer element (mostly capacitive) and want to make sure that I am using the best (lowest noise) OpAmp for the job so I need to find out if Voltage noise or Current noise is the dominating factor.

See attached. I have attempted to reduce the circuit for analysis as much as possible and have used En x gain to find the output referred voltage noise but am unsure how to find the current noise. Not sure if I its valid to make it output referred by multiplying by the gain. Not sure if I need to combine the effect from the feedback resistors. I think I do but not sure how.

I realize for a full analysis I should include the resistor Johnson noise but I am not worried about that right now.

I am designing a preamp for a type of transducer element (mostly capacitive) and want to make sure that I am using the best (lowest noise) OpAmp for the job so I need to find out if Voltage noise or Current noise is the dominating factor.

See attached. I have attempted to reduce the circuit for analysis as much as possible and have used En x gain to find the output referred voltage noise but am unsure how to find the current noise. Not sure if I its valid to make it output referred by multiplying by the gain. Not sure if I need to combine the effect from the feedback resistors. I think I do but not sure how.

I realize for a full analysis I should include the resistor Johnson noise but I am not worried about that right now.