LDMOS transistor stability and feedback

[makkawi22]

Hi every one....
I'm working on an RF PA (Polyfet L2711) , but I face some troubles in the drain current . when I turn the PA on it start with maximum current (as designed) and it decrease along its ON, this problems happen at some frequencies with different rates . I think it is the output matching but first I want to Know about feedback. Does it change the input /output impedance of the PA and if yes how to to calculate it .. Thanks

 

[tony_lth]

surely the feedback change everything. One way is to simulate it.

 

[makkawi22]

thanks for interesting @tony_lth.
I'm using ADS 2011 ... do I need to start simulation with feedback first or the matching networks

 

[BigBoss]

This seems to be temperature drifting problem,not impedance changing or something else.
Check your bias circuit and temperature stability of your system.

 

[Ow@i$]

i don't think so that matching can cause this.. surely either temperature or feedback ... you gotta have to check both

 

[hkpradeepkumar]

Hi every one....
I'm working on an RF PA (Polyfet L2711) , but I face some troubles in the drain current . when I turn the PA on it start with maximum current (as designed) and it decrease along its ON, this problems happen at some frequencies with different rates . I think it is the output matching but first I want to Know about feedback. Does it change the input /output impedance of the PA and if yes how to to calculate it .. Thanks

Hi brother.. if possible can u tell me how did u stabilize u r transistor.. i am also using the same transistor for my design, i did stabilize my transistor.. but i am not getting high S21 which i need.. so if possible send me u r schematic to my mail id.. hkpradeepkumar@gmail.com.. i hope u help me..