I need some help confirming if my math is right.
Trying to calculate the input-referred noise in this OPA2626 circuit.
*Rf is lower than Rin; this is a non-inverting signal-attenuation application where 20LOG(Vout/Vin) = -1.16dB
These are my calculations (excel sheet)
I used this document for equations and calculations, along with some values/graphs in the OPA2626 datasheet.
1) Calculate the thermal noise due to (-) input feedback resistors (R1||R2)
2) Calculate the thermal noise due to (+) input signal resistors (R3||R4) (same eq. as 1) but with R3||R4)
3) Calculate opamp (-) input rms voltage due to current noise
4) Calculate opamp (+) input rms voltage due to current noise
5) Calculate opamp input rms voltage from voltage noise
6) use sum-of-squares to sum the rms voltages and get our input-referred noise voltage (RMS)
The result here I get is ~225uVrms input-referred noise.
Since the noise gain is Gn = 1 + R2/R1, I multiply the input-referred noise by Gn.
Thus, the final output voltage noise I get is ~421uVrms.
Given the schematic shown above, can I get a 2nd opinion on if these equations/calculations give an accurate result?
For one, I'm not completely certain if my actions for step 2) above are right.
Much appreciated...!
Regards,
Darren
