What Output Impedance Should I Use for LNA Simulation in ADS When Not Matching to 50Ω?

Hello guys,

I have been busy with a problem for couple of days. I will be more than grateful if you help me with this.

I am new in RF design and I am trying to simulate a simple LNA with ADS. My problem is, I do not want to match my LNA's output to 50ohm because, it is in the chip and it will be connected to mixer.

My question is, when I put terminal at the output of LNA what should be the Z of terminal. Without output terminal I am not able to observe noise and some other parameters. I can just plot S11.

best,

Ata
 

The problem is, I want to use mixer after lna, therefore my next stage will be the gate of transistor. I found rf nmos transistor input impedance at 1Ghz and it is like a+bj. But problem is, here a equals 600 ohm which again requires matching. I cant understand why they say inside chip we dont need matching. In high frequencies like 1GHz input impedance drops from 1 meg to 600 !!!! Im totally confused.

this is the simulation

so Zin= 13 - 322j !!!!!

Hi Ata,

You need to establish a conjugate match at the output of the LNA for maximum power transfer.

Regards,
Sanat