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Design >> RF Design >> Linear RF Power Amplifier stability--very urgent
https://designers-guide.org/forum/YaBB.pl?num=1371041516

Message started by purplewolf on Jun 12^th, 2013, 5:51am

Title: Linear RF Power Amplifier stability--very urgent
Post by purplewolf on Jun 12^th, 2013, 5:51am

Hi,
How to correctly measure the stability of Linear CMOS RF Power Amplifier?
Supppose I have biased my amplifier at Vbias = 1.3 Volt with supply VDD of 3.3 V. I check the K-factor and stability circles at this point and it is perfectly stable. But since the signal is large so should i check the check the stability at each and every DC bias point meaning i run a nested DC sweep from 0-3.3 V inside the s-parameter sweep?.

which one is correct way? Because if the stability is check at all DC bias points then its unstable at some bias points (usually at Vth) and as a result gain has tro be sacrificied. I am confused about this point.
I have a tape-out coming and i dont want to do a mistake.

I woul appreciate your help in this regard!

Title: Re: Linear RF Power Amplifier stability--very urgent
Post by Frank Wiedmann on Jun 13^th, 2013, 1:42am

I suggest that you perform transient simulations for all relevant operating conditions (input amplitudes, input step sizes/slopes, load impedances, power turn on/off, etc.) and look for undesired behavior like ringing, voltage/current limits of devices, etc. When a circuit operates under large-signal conditions, a series of small-signal simulations does not capture its behavior very accurately in most cases.

Title: Re: Linear RF Power Amplifier stability--very urgent
Post by purplewolf on Jun 13^th, 2013, 2:20am

i check load source impedances, input amplitudes but they are okay. but the issue is i see k-factor around 0.5 (when i DC + s-parameter sweep combined) near Vth although i my bias operation is around 1.5 V which is far 'beyond' 0.5 V.I wonder when high input power will be applied will it become unstable when the RF Signal crosses 0.5 V. This is how i understand 'large signal behaviour'.
I think u understand my point here.

Title: Re: Linear RF Power Amplifier stability--very urgent
Post by purplewolf on Jun 13^th, 2013, 2:27am

if i was to desgin LNA. I would check LNA stability at one DC BIAS point as its is not a large signal block. But for PA its a different case.!!