Help me determine BFS17 out impedance

Hi all,

Newbie in RF, sorry for stupid question.

I try to design a PI filter to match some BFS17 to 50ohm and reject spurs on 10MHz. I use RFSim99 and I found 2 cell PI it's ok but how to determine out impedance of BFS17 to introduce is RFSim as PORT for filter?

From NXP site I found a lot of S2P files and I choose common emitter, 10V and 20mA witch is best fit for me.

Can anyone tell me how to determine his out complex impedance for specified freq.?

Thanks in advance,

no one for help here ?

RFSim99 has an Auto Match option. The easiest way is, to design first the 50 ohms output match of BFS17 (Low Pass topology), and attach at the output a 50 ohms LPF (calculated before). Ideally would be to integrate the LPF into the output match, to minimize the number of components. For this you need to use the tune option, checking for inband gain and out of band rejection.

Ah...ok. That's fine.

In fact I try to use MMBT2222 because my app it's on 10MHz but I couldn't find any S params for this ordinarily transistor :) Due to high gain of BFS17 compared to 2N2222 for high freq., I have now a lot of measured harmonics on 400MHz, arround -80dB, after this LPF.

Doesn't matter, thanks anyway.