stenzer
Advanced Member level 3
Hi,
I'm calculating the noise of an inverting opamp followed by a variable gain amplifier. The opamp's noise sources are stated by its input current noise and input voltage noise in pA/sqrt(Hz) and nV/sqrt(nV), respectively. I calculated the opamp's output rms noise voltage.
The output of the opamp (1st stage) is connected to a variable gain amplifier (2nd stage). I calculated the cascaded output noise caused bei the 1st stage (opamp) by Vn_opamp^2 * G(x), where the VGA amplification G(x) is a function of the gain control setting x.
Now I'm getting a little bit confused. The VGA noise is given by its noise figure NF in dB. This noise figure is also a function of the gain setting x and decreases with increasing gain. How can I convert the noise figure into a rms voltage noise, to calculate the total noise of stage 1 and stage 2?
The VGA has an input impedance of 200 Ohm, if this helps.
Can anyone tell me how to calculate the total noise?
BR
I'm calculating the noise of an inverting opamp followed by a variable gain amplifier. The opamp's noise sources are stated by its input current noise and input voltage noise in pA/sqrt(Hz) and nV/sqrt(nV), respectively. I calculated the opamp's output rms noise voltage.
The output of the opamp (1st stage) is connected to a variable gain amplifier (2nd stage). I calculated the cascaded output noise caused bei the 1st stage (opamp) by Vn_opamp^2 * G(x), where the VGA amplification G(x) is a function of the gain control setting x.
Now I'm getting a little bit confused. The VGA noise is given by its noise figure NF in dB. This noise figure is also a function of the gain setting x and decreases with increasing gain. How can I convert the noise figure into a rms voltage noise, to calculate the total noise of stage 1 and stage 2?
The VGA has an input impedance of 200 Ohm, if this helps.
Can anyone tell me how to calculate the total noise?
BR