amplifier voltage and current noise

Hello Jeff,
The broadband voltage noise of the amplifier will scale similar to a thermal resistance model (4kTR). I will need to check with the designer on the current noise model and get back to you.
-Samir

Jeff,
Given that this is a JFET input amplifier with low input current noise, is the current noise spec critical? Is the source impedance very high?
-Samir

the bias current of JFEt is so low I don't think it is critical in this design.

Jeff

even though it is low what is the model like for the current? the input of opamp is a photodetector. has very high output resistance, in 100Mohm range.

Are you saying the voltage noise of opamp will reduce by 2 if I lower the temperature by 4 times?

Hello Jeff, The temperature in the equation is in Kelvin, not Celsius. It will follow the thermal resistance model. So for example a 1.5KOhm resistor @ 25C has a noise of 4.9nV/rtHz. At -40C that noise calculates to be 4.4nV/rthz. I am using the noise calculator here:
www.daycounter.com/.../Thermal-Noise-Calculator.phtml
For current noise, the designer let me know that the current noise is directly correlated with the gate leakage current(Ig^2= 2*q*I_Gate). The gate current will double for every 10ºC rise in temperature so the current noise will follow.
-Samir