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Stability of a Balanced Amplifier - RF Cafe Forums

The original RF Cafe Forums were shut down in late 2012 due to maintenance issues. Original posts:

Amateur Radio | Antennas | Circuits & Components | Systems | Test & Measurement


ljoseph
Post subject: Stability of a balanced amplifier Posted: Sun May 04, 2008 8:08 am

Captain


Joined: Tue Sep 04, 2007 7:54 am
Posts: 13
Location: Dallas
I have a balanced amplifier with Avago's ATF58143 pHEMT. The balanced amplifier is unconditionally stable, but the the individual stages are not. Is this OK?. Elsewhere I read that we need not care stability of Individual stages...just make the total balanced amplifier stable.
Please let me know your thoughts on this.


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IR
Post subject: Posted: Wed May 07, 2008 3:57 pm

Site Admin


Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello ljoseph,

In principle you should not be concerned about each stage. One of the advantages of balanced amplifier is the improved impedance matching both at the input and at the output of each stage (Due to the quadrature couplers), this improves the stability of each of the amplifiers. When each amplifier works as a stand-alone unit, it is therefore much less stable due to degraded matching and is prone to oscillations.


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Tony Kurlovich
Post subject: Posted: Fri May 16, 2008 5:37 pm

Captain


Joined: Thu Oct 19, 2006 6:02 pm
Posts: 7
In a balanced amplifier, there is the risk of common mode oscillation in an apparently stable device.





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