A 50-ohms port is used as the input noise source. Somebody told me to place a extra 50 ohms resistor in parallel with this port to simulate the NF of the circuit. Is it right??
Same questions arises in the IIp3 simulation for the same circuit. Is it right to place a resistor in parallel with the port?

Thank you.

zhangjerome wrote on Jun 30^th, 2008, 10:42pm:

Generally it is not correct.
See the follwing.
http://www.designers-guide.org/Forum/YaBB.pl?num=1194006190

zhangjerome wrote on Jun 30^th, 2008, 10:42pm:

As far as lumped component level simulation, such shunt 50ohm is not needed. In this case, you don't have to use port. You might use vsource depending on your application and purpose.

But if you use actual signal generator of relative high frequency, such shunt 50ohm might be needed since signal is fed through 50ohm line.
See http://www.designers-guide.org/Forum/YaBB.pl?num=1207009725