Problem in S-parameters of LNA.

I have designed LNA.I am getting s11 constant(straight line).

Also same thing for simple R L C series circuit.

Plz help..Why correct s11 is not coming.

Thanks..

Hi,
more info are required to answer you.
Anyway a simple guess could be that for some reason you are not performing a frequency sweep analysis ...
Max

There might be calibration,cable,connector etc. issues.

I am supposing rfuser talking about simulation.
BigBoss is supposing rfuser talking about measurement.
So please rfuser, explain better.
Max

S..Sure I explain my problem in better way..

Actually I am doing simulation of LNA on Hspice RF,and seeing results on cosmoscope..but not getting
S-parameters plots correctly as ususally it should be..
I am attaching Spice code for LNA, please rectify my problem...
Thanks..

Please reply,If can rectify my problem.

thanks

Hi rfuser,
have you read my first post?
What I read in the row in your project file:

.param freq1=1.91e9 freq2=1.91e9 power=1e-3 Vdd=2.3

does it means you are not sweeping frequency?

Have a trial and let us know ...

Hope this helps,
Max

I am new in RF design and cadence spectre simulation. About the s parameter. what we should expect? In another word, in which range for the s parameter, indicate the LNA is good or bad?

Thanks.

What's your application? What's your requirements? The S paras is dependent on your requirements.

I am learning RF design and that's my first assignment to design and simulate a LNA. I just caculated the parameters for simulation. But the simulation result is quite different from the caculated values. I change the load inductor to make the S11=-3.98dB, S12=-47.54dB, S21=11.737dB, S22=-7.29dB, K=14.65167, NF = 3.734dB.

I am not sure those figure is OK or that's a bad design.

Another thing is I also change the inductor to the Gate (Lg) smaller and I hope to check the input impedance if it is matching but I don't know how to do that in Spectre.
Can anyone give me some help?

thanks

What is your freq? for Ka, NF is good.

The freq is 2.55GHz

You can refer the specifications of famous vendor, such as Mini-Circuits, Hittite, etc.

You can also refer some RF textbook like Thomas H.Lee or others.