LNA stability on high frequencies

[ltrlspree]

Hi,

How can I check stability on an LNA above the maximum I can see at my Network analyzer? Example, I have a NA up to 8 GHz and would like to know if my amplifier is doing ok in stability till 20 GHz.

I understand there are a few practices one can do with an spectrum analyzer.

Any idea or documentation I can look at?

Thx!

 

[jayce3390]

What is the operating frequency band of your LNA?

Of course, the best way to check should be the spectrum analyzer.

 

[ltrlspree]

2.4 GHz. Any ideas?

Thx in advance

 

[jayce3390]

I posted something more but disappeared...:-(

Where is the low power level input signal? Both input frequencies show similar power levels, seems weird.

 

[fausteric]

Hi,

How can I check stability on an LNA above the maximum I can see at my Network analyzer? Example, I have a NA up to 8 GHz and would like to know if my amplifier is doing ok in stability till 20 GHz.

If you now the cutoff frequency (frequency at which the gain is 0 DB) off the used transistor then you know that above this frequency the LNA must be stable sinds the gain is below 0 dB.

 

[BigBoss]

Simply connect a SA at the input and observe the possible oscillation up to fmax of your technology...Decrease the RBW down to minimum possible to be ale to see lower oscillations.
Because if you don't observe higher frequencies up to fmax, possible oscillations will degradade you LNA perfomance.

 

[jayce3390]

Question :

Without using Spectrum analyzer. If you perform a frequency sweep (with constant power) of the main input signal and observe the drain current ? If it's ringing that reveals a start up of an oscillation. I m wrong?

 

[tony_lth]

Except link SA at input, you can also link SA at output, without input, if you can see some spurs or noise floor is raised, then it's osc.