how to get PA output Ropt ?

Dear all:
I design 2.4GHz class A power amplifier.
Vdd=2.7v , Idc=1e-3
Vg=0.7v ,

according formula

Ropt=2.7÷1e-3 =3k

is that right ?

because my colleague told me the value is too large .

i don't know why . somebody can tell me ?


thanks .

Thank your colleague!

Please elaborate on your question

Ropt=2*(Vcc-Vsat)/Ic(max)

if Vcc=2.7V , Idc=1mA so Imax=2mA (two times of Idc for symmetric operation) and we assume Vsat=0.25V

Ropt=2*(2.7-0.25)/2E-3=2450 Ohm.
With this Ropt you'll find 1.225mW output power that is not "really" power amplifier..

Load Line theory is only used to predict "range of load impedance".In other hand, there are many parasitic factors that influence the operation. So this design should be simulated in a Load Pull featured simulator with high accuracy nonlinear models.

t think if you have a nonliner model,you should try load pull methods to find
the best impedance of the Ropt.
ansoft designer,ads, mwo these cad tools all have this method.
good luck to you.

I use TSMC 0.25um process , they don't have large signal model.

1. So according BigBoss Ropt=2.45k and match to 50 Ohm ,
2. I also run load-pull 1db contour , the Ropt=113+j271 @Ropt=2.7k
and match to 50Ohm
3. set Ropt=300Ohm

The reult is Ropt=300Ohm have max power then 113+j271 and 2.7K.

so formula is correct ? Or I'm miss the message .

Thanks ...

Usually in P.A. you have the Pout. So according the Pout you have you can calculate the Rout you must match
Rout = (Vdd_Vsat)^2/(2*Pout).

regards

i had try the method that BigBoss and molloy suggestion, Ropt=2450 have max amplitude and power ..

I have another question
1. the nolinear model is equal large signal model ?
2. when run 1db contour need input matching ?
3. I don't have large signal model can run 1db contour ?


thanks ...