S11 and S21 parameters for LNA design

[srividhya murali]

Hi,
Im using 0.18u technology to design an LNA using cadence. According to the specs, Im supposed to get S11=-13.3dB and a gain of S21=16.6dB.the freq that I musing is 5.2G Hz
Could you give me some suggestions to reduce the reflections at the input (from S11=-2dB to -13.3dB ) and increase the gain?
This is my first design, and I appreciate anybody who could help me out with this
Thanks

 

[BigBoss]

Better input matching will improve the reflection coefficient and increase the gain...
But if you goal is to obtain low noise simultaneously, in this case you should find the optimum matching that will bring you lower reflection and less noise...

 

[Abhishekabs]

Your NF will degrade if your S11 improves.
It is a trade off.
Thats why people go for 2 or 3 stage of amplifier.
First stage LNA decides NF of the complete system.

What is NF you are getting for S11 or -3dB & S11 of -13dB ?
& what is required one?

 

[tomtomson]

In order to get a better S11 and maintain your NF, you need to use inductive source degeneration. So, a pretty standard, typical LNA in cadance would be a cascode configuration with a small inductance at the source of the bottom device and some inductance at the gate of the bottom device should get your noise, S11, and S21. This is because the source degenerated inductance will bring your optimum noise impedance closer to your S11 conjugate.

 

[kmmaran]

Basically the low S11 the better the input reflection, the reason is, your point S11 will move to 50ohm in the smith chart. If you not considering NF (which you supposed for LNA design) then simply move your S11 point to 50ohm in smith chart. This is only applicable to get S11 to low and Reflection Coefficient to 0.

 

[srividhya murali]

Thank you so much everyone! Right now Im able to achieve a good S11, S21. but just want to know how I could reduce my my s12 from -32 to -53 dB. and also how do could I also improve my S22??
Thanks and I appreciate it!

 

[gogo1222]

Thank you so much everyone! Right now Im able to achieve a good S11, S21. but just want to know how I could reduce my my s12 from -32 to -53 dB. and also how do could I also improve my S22??
Thanks and I appreciate it!

S12 is an isolation problem, you can add a source follow in the end which will be help you.