Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would
be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate
that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views.
It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if
you would like to post something on RF Cafe's
page, please do.
Below are all of the forum threads, including all
the responses to the original posts.
Post subject: stability in Power amplifier Posted: Tue Feb 27, 2007 9:56 am
Joined: Tue May 02, 2006 4:59 am
How can I simulate and calculate stability in power amplifier ?
In small signal i can use the s-parameters for that (K>1 and |delta|>0) but in power amplifier the s-parameter is not available because its define only for small siganl.
Post subject: Power amplifiers and S-ParametersPosted: Wed Feb 28, 2007 3:46 am
Joined: Wed Feb 22, 2006 3:51 pm
Let's phrase your objection more precisely:
Manufacturers do not provide s-parameter data for their transistors when used in anything other than Class A amplifiers.
Large signal amplifiers certainly reflect power. Measure the magnitude and the angle of the reflection, and you can calculate an s-parameter.
S parameters vary unpredictably when a transistor is driven into nonlinear operation. By "unpredictably" I mean that they depend on parameters that vary from device to device, and which aren't usually measured or listed at all.
There are entire books written on the subject - Cripps has written two good ones (check www.artechhouse.com).
Post subject: Posted: Mon Apr 09, 2007 9:37 pm
Joined: Tue Mar 15, 2005 11:43 pm
I agree with fred47.
S-parameters are not limited to small-signal. Let's put it this way, S-parameters are basically port-to-port measurement, it can be small-signal and large-signal. It depends on the measurement (power) conditions.
According to experience, stability can be defined well by small-signal, by defining K and delta. Most of cases, it wont change too much in large-signal. Unless, there are some "unwanted" positive feedback happens or driven transistor to extreme bias point.
I hope it helps.