Hello everyone,

I have managed to design a Class-A amplifier at 1 GHz (see attached) using ADS
Now, I have to drive it harder to move it from class-A to class-C (From linear mode to non-linear)
I did some modifications on the circuit but I am not quite sure about the correct steps!
I have to investigate into how the resonant circuit affects the output power, and then the efficiency as a function of a conduction angle and so on.

Is there anybody can help with the right starting off steps please?
N.B: I am still new to an RF design world, so please make it simple as much as you can

Your help is much appreciated

 

Welcome to AAC!
Is this a school/college assignment?

 

Welcome to AAC!
Is this a school/college assignment?

Thanks Alecc_t
Actually, this is part of my MSc dissertation, I am not familiar much with RF design
So is there anyone to help!?

 

Good morning
Anyone is willing to help please?

 

Hello,

How much input power would you need to activate the transistor?

Bertus

 

Hello,

How much input power would you need to activate the transistor?

Bertus

Hi Bertus

Thank you for your reply.
I'm using BFP740F transistor and I don't know the actual value (I didn't find in the datasheet )
I have calculated L and C values of the tank circuit to be resonating at 1 GHz but I am getting this output current waveform and I don't know what do I need to do!!!
Please see attached screenshots of what I have got so far
Also please be patient as I am don't have a previous experience in RF
Thank you for your understanding

 

Hello,

The datasheet only shows the Class A characteristics of the transistor.
For Class C, there is no base current.
To activate the transistor, there should be enough power on the input to have the transistor activated (create a base current).
This usualy happens when the input voltage is over the B-E limit voltage.

Have a look at some RF power transistors, how those schematics and characteristics are used.

Have a look at the attached PDF about Class C.

Bertus

 

Hello Betrus,

In order to find the optimal value for tank circuit component, I have to calculate the Q factor first which can be calculated as Q=Fc/BW
Next, the source and load resistance are combined to determine the total parallel resistance of the circuit using Rp= Zs.Zl/Zs+Zl
After that the parallel reactance could be determined using Xp=Rp/Q
Finally, by substituting in L=Xp/w and C=1/w.Xp we can get the L and C value
The problem is in determining the source and load impedances as I thought they could be calculated using the input and output conjugate (as you can see in the attached screenshot) and I'm really confused!
Could you please advise?
Thanks