While simulating differential LNA I noticed that the gain reported by the Pnoise Transfer Function is significantly different than the voltage gain from a straight PSS simulation. The particulars of the circuit are Zin = 100 Ohm, Zout = 800 Ohm, Av(unloaded) =  29.4dB. The input port is set 60dBuV (1mV). I deliberately mismatch the input and output with Rs=800 Ohm and RL = 100 Ohms. The PSS sim reports a voltage gain of 10.33dB as expected but the Transfer Function from the pnoise sim is -2dB??? I cannot find in the manual how Pnoise calculates the gain. Any thoughts? Why is the pnoise gain so different than the PSS gain?

Thanks for the info. That helped Basically what it said is that the voltage gain is defined as Vout/Vin but the Noise gain is Vout/Vs so you have a badly mismatched case as I did with Rs=800 and Rin =100 there is an additional attenuation of the equivalent input noise source at the input of the DUT.