Recently,I did some simulations and I find when I measure the Amplifier's noise figure in ADS,the input noise power is different from what it should be.Here is my simulation process.

The bandwidth is 1Hz. The simulation results are as follow.

This is different from what it should be.Recording to the equation Pn=kTB, we already know T=290k and B=1Hz,so we can get Pn.

And then, I made some another attempts, put off the amplifier and measured directly.

The simulation result is generaly equal to Pn.

I use attenuation substitude amplifier and made a same measurement.

We can get same anwser!

Return to the begining, Why we use amplifier the input noise will change? Please help me to solve this problem.

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