Problem in S-parameters of LNA.

• Jan 5, 2011

• #1

R

rfuser

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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..

 

• Jan 5, 2011

• #2

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Mad2Max

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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

 

• Jan 5, 2011

• #3

BigBoss

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

 

• Jan 5, 2011

• #4

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Mad2Max

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

 

• Jan 5, 2011

• #5

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rfuser

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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..

 

Attachments

• LNA.txt

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  LNA-S-param.png

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• Jan 8, 2011

• #6

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rfuser

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Please reply,If can rectify my problem.

thanks

 

• Jan 10, 2011

• #7

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Mad2Max

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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

 

• May 2, 2011

• #8

E

enchanter

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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.

 

• May 3, 2011

• #9

tony_lth

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

 

• May 3, 2011

• #10

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enchanter

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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

 

• May 4, 2011

• #11

tony_lth

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

 

• May 5, 2011

• #12

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enchanter

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The freq is 2.55GHz

 

• May 6, 2011

• #13

tony_lth

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

 

• May 16, 2011

• #14

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rfuser

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