LDMOS transistor stability and feedback

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makkawi22

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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
 

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

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

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

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

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..
 

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