How to drive transistor into saturation mode(switch mode) using RF modulated PWM

[pYrana13]

Hi all,

I need to design Current Mode Class-D (CMCD) PA with modulated PWM signal as an input and encounter these problems. I describe step by step the design I done and the problems I encounter in the pdf file below.
Hope any of you can show me which part I did wrong.

Thanks a lot.

 

[BigBoss]

Even you question is nor clear, let me tell you what I have understood..
You would make your transistor by driving this non-zero mean valued RF signal to amplify as Class-A ??
If you want to see 180 degree drain current, you should bias your transitor above treshold and your driving signal will be rail-to-rail with these values.
It's all about my understanding...

 

[mtwieg]

That document makes sense up until your actual question, which I can't make sense of. For driving a CMCD, or any SMPA in general, you usually DC bias the gate voltage slightly below the threshold (or pinch off in your case), so that nothing conducts if the RF input is turned off. The AC component of the gate drive must be high enough such that the FETs are driven well into their linear region of operation (not saturation, unless you're using bipolar devices).

 

[pYrana13]

That document makes sense up until your actual question, which I can't make sense of. For driving a CMCD, or any SMPA in general, you usually DC bias the gate voltage slightly below the threshold (or pinch off in your case), so that nothing conducts if the RF input is turned off. The AC component of the gate drive must be high enough such that the FETs are driven well into their linear region of operation (not saturation, unless you're using bipolar devices).

Thank you for your reply. Could you please elaborate more of this part. I still cant understand what u meant. TQ