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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


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Post subject: Gain expansion
Unread postPosted: Fri Jul 15, 2005 2:04 am

Hello,
In a three stage amplifier that I have designed (pHEMTs as active devices), I am noticing an substantial gain increase (about 3 dB) with input power. The small signal gain is down 4 dB from the simulated value but starts to go up with input power before the gain starts to compress. The gain 'expansion' is also so steep it almost looks like there is a discontinuity in the Gain/Pin curves. Return losses are close to simulated values. Any ideas on what might be causing this?


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IR
Post subject:
Unread postPosted: Fri Jul 15, 2005 2:43 am
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Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany
Hello,

The situation you described is common in several transistor technologies. It is mostly related to bias level the transistor gets and can be emphasized or de-emphasized with lower or higher bias respectively.

This gain expansion as gain compression is considered as non-linearity.

You can make this useful, if you plan to use some sort of of linearization scheme for your amplifier.

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- IR


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IR
Post subject:
Unread postPosted: Mon Jul 18, 2005 12:53 pm
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Joined: Mon Jun 27, 2005 2:02 pm
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Just a clarification to my previous post: By bias level, I meant for example the Vgs voltage level in JFET's/MESFET's

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- IR


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