serious problem of stability

[abdoeng]

after adding resistance at drain,the stability near (.9-1)(k factor),any method to control the stability more easily.
if i use steop impedace,how i optimize it with its t.l. at both sides.,the opt. chang its width rather than not equal to its ended t.l.
any methods to optimize it
regards

 

[vfone]

Try to add a small resistor value in source…just to see if you can stabilize.
I know the NF will go up, but is an indicator.
Usually, if for stability is looking for a high resistor value in source, means that the input match need a different topology.

 

[dsjomo]

Design a two-stage LNA, and make the interface mismatch. And check the following things---

1) the output resistance of 1st stage lies in the stable region of 2nd stage's input stability circle plot.
2) the input resistance of 2nd stage lies in the stable region of 1st stage's output stability circle plot.

Adding a resistor at any of the 3 port is the most easiest way to solve the stability problem. Or try another way --- lower down the bias current.