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stability in Power amplifier - RF Cafe Forums
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Noise
Post subject: stability in Power amplifier Posted: Tue Feb
27, 2007 9:56 am
Captain
Joined: Tue May 02, 2006
4:59 am
Posts: 15
hello,
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.
thanks
noise
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fred47
Post subject:
Power amplifiers and S-ParametersPosted: Wed Feb 28, 2007 3:46 am
General
Joined: Wed Feb 22, 2006 3:51 pm
Posts:
104
Hi!
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.
What gives?
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).
Good Luck!
Fred
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Jeanalmira
Post subject: Posted: Mon Apr 09,
2007 9:37 pm
General
Joined: Tue Mar 15, 2005 11:43
pm
Posts: 65
Location: Singapore
Hi :
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.
Cheers,
Jean
Posted 11/12/2012
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