Please Help me with Power Amplifier!! Plz~

[aliceseo]

Hi
I am planning to make Doherty Amp.
I designed Class A model on ADS for start but I am stuck with some questions.



I have attched a picture in word file. You will have to just mention about what voltage (Vds of 4.5V) and current( drain current of 280mA) the bias network is designed for.

Say for instance i use R2 and R3 to be of 100 ohm and 4.7 ohm while R1 to be 22 ohm resistor i would expect Vds of 4.5 and Id of 280mA when Vgg is 10V and Vdd is 10.66V.

R1 is of 7 watt in the drain side just in case for AC operation. while R2 and R3 are normal quarter watt. Just want to know why am i not getting any drop in R1.

And Also I am a bit confuse with how I can change the Class of Amplifier.
I designed Class A with Fixed bias point same as above but I am not sure
how can I change to different Class.

I will be really really really thanks if anyone helps me and gives me lots of advise.


Have a nice day to everyone~
THanks,

 

[aehoward]

You change the class of operation by adjusting the bias and input signal amplitude such that the conduction angle is reduced. In Class A, the conduction angle is 360 degrees, meaning that the device is on for the full cycle of the input sinusoid. You can shift the bias point such that it is on only for say half of the input cycle. This should increase power-added efficiency. The books by Cripps talk about this.