Hi,
Could someone tell me what are the methods of calculating a collector (dren) inductor value in an RF power amplifier? I mean the one that connects the collector of a transistor to Vdd.
I thought I knew how to do it but yesterday some guy told me about his method, which is different than mine, and I am very confused now.
The RF Power Amplifier inductor placed between collector (or drain) and Vcc, generally is a choke. The DC resistance of this choke shall be very low, to do not affect the PA efficiency.
It varies from point of application
Let say for DC you need choke
for in band tuning use calculations
for harmonic suppression again use calculations.
etc.
Is it still a choke in case of a wideband amplifier (LNA) ?
Someone told to pick the value of that inductor in such a way that it has the same impedance at the operating frequency as a resistor that would have been there to get Vdd/2 at the collector for a given operating point (Ic).
Say you have 12V Vdd and Ic=100mA operating point, hence Vdd/2=6V.
6V/100mA=60ohm
2*pi*f*L should be 60ohm
Is this theory wrong?
Is it still a choke in case of a wideband amplifier (LNA) ?
Especially for a wideband LNA the inductor must be a choke. Some wideband LNA applications (where power efficiency is not important) uses also a resistor in series with the choke.