NF of Common_Gate LNA

[nxing]

I am going through some design equation of LNA NF calculation and found that for Common-Gate CMOS LNA, if the input resistance is matched with 1/gm, then the NF=1+gamma, independent of the load R (i.e. Gain of the amplifier), this is sort of contradict of my intuition, Is it really the case?

Thanks

 

[summerock]

HI
if we only consider the thermal noise ,the NF =1+γ/α+4RS/RL,(RS=1/gm)
,so it does not independent of the load RL .
:|

 

[derek_lkm]

Hi,

Pls refer to Thomes Lee Book Chapter 12 on LNA, think he gave a pretty detail insights. Anyway i got it worked out, email me if you require the exact steps.