Input impedance problems in LNA design

[kella]

Hello friends

I am trying to design LNA but I got some problems there. I have attached the schematic and simulations. Can some one tell me whats the problem with input impedance? how can i improve the input impedance?

thanks

/k

 

[kella]

[HELP] LNA Design

is my question very hard to answer or my english is very poor to understand?

Friends plz help me.

/k

 

[sanim]

Re: [HELP] LNA Design

Hi,

You use in your design cascode configuration with resistive feedback. In this case input impedance is equal to (Rl+Rf)/(1+gm*Rl), where Rl and Rf are the load impedance and feedback resistor respectively. Moreover input impedance can be estimated as Rf/Gain. In simulation you got gain ~ 3 (=10dB). So input impedance is 560/3 ~ 180Ohm. By tuning Rf you can set proper Zin. But please keep in mind that decreasing Rf results in higher NF.

Rgds
Victor

 

[kella]

Re: [HELP] LNA Design

Hi,

You use in your design cascode configuration with resistive feedback. In this case input impedance is equal to (Rl+Rf)/(1+gm*Rl), where Rl and Rf are the load impedance and feedback resistor respectively. Moreover input impedance can be estimated as Rf/Gain. In simulation you got gain ~ 3 (=10dB). So input impedance is 560/3 ~ 180Ohm. By tuning Rf you can set proper Zin. But please keep in mind that decreasing Rf results in higher NF.

Rgds
Victor

Hello

thanks victor for the reply. Yeah if I decrease the Rf then i will have to face the higher noise figure problem. So is there any other solution to this?

regards

/K