Re: Simulated RF amplifier stability, but with a filter?

"billcalley"
>
> This has been really bugging me:  When I design and simulate an RF
> amplifier (LNA) for a class project, it shows points of huge
> instability (below the desired passband 'K' is *way* under 1 ).


** K is a measure of the  *potential* for an RF amplifier to oscillate.

A K value less than one means that oscillation possible, with the right 
combination of input Z and load Z.


 > But
> when I add a bandpass filter to the input of the unstable simulated
> amplifier, the instability is "gone" (the K is now way above 1).


 ** The BP filter eliminates a whole *range of values* for input Z from
the 
game  -  so eliminates the main cause of possible oscillation.

This link might be of interest:

http://www.daycounter.com/Calculators/Complete-RF-Amplifier-Design-Analysis-Calculator.phtml



.......   Phil