Strange NF value of the LNA.

Dear all,

I have designed one simple source degenerated LNA. However, the simulation result is strange to me. For the first setting of components value, it gives me high NF. As I change the larger value of the drain inductor (LNA loading inductor), it could give out the lower NF value and still in same voltage gain. I have checked the DC current consumption is same. Moreover, I have seen the noise contribution of each component, the new setting value of inductor create 50% less noise contribution. I still don't know why . Could anyone explain it?

Thanks

wccheng

Hi chi,

NF is the snr difference, the larger the output signal, the smaller the noise figure. The larger the output inductor, the larger the output, right?


Demigod+

yeah i agree , u have increased the gain of the amp and so the NF is decreased

khouly

Dear all,

I have done a simulation several times. I found that this is due to the noise match between output of LNA and the input of mixer.

thanks

wccheng