megaknaller
Member level 2
Hi,
From reviewing the classical input impedance of an LNA with inductor degeneration (assuming CMOS), it is known that by adding the degeneration inductor, the input impedance looking into the transistor has a real component Re{Z_in} = (g_m * L_s) / C_gs. So if the input of the LNA is matched to the source, there is a net power delivery into the circuit, but the full input circuit consists of a resonance circuit in which the only physical resistance (ideally speaking) is the R_s of the source since the other L's and C's cancel out.
From the equation above, it seems that the g_m of the transistor is actually transferred to the input but I still don't get the full picture where is the input power actually being burnt? Could anyone help to clarify this? Or cite some interesting source about it?
Thanks!
MK
From reviewing the classical input impedance of an LNA with inductor degeneration (assuming CMOS), it is known that by adding the degeneration inductor, the input impedance looking into the transistor has a real component Re{Z_in} = (g_m * L_s) / C_gs. So if the input of the LNA is matched to the source, there is a net power delivery into the circuit, but the full input circuit consists of a resonance circuit in which the only physical resistance (ideally speaking) is the R_s of the source since the other L's and C's cancel out.
From the equation above, it seems that the g_m of the transistor is actually transferred to the input but I still don't get the full picture where is the input power actually being burnt? Could anyone help to clarify this? Or cite some interesting source about it?
Thanks!
MK