A common gate configuration LNA is shown in Figure 1(a). The equivalent circuit is shown if Figure 1(c).
The gain of LNA is,
(1)
(2)
Noise factor
MOSFET channel noise only considered here for NF calculation.
Noise power added by the circuit referred to the output is ,
Noise power at input
Noise factor of the circuit is
(3)
When , noise factor is
(4)