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RF Cafe Forums closed its virtual doors in late 2012 mainly due to other social media platforms dominating public commenting venues. RF Cafe Forums began sometime around August of 2003 and was quite well-attended for many years. By 2012, Facebook and Twitter were overwhelmingly dominating online personal interaction, and RF Cafe Forums activity dropped off precipitously. Regardless, there are still lots of great posts in the archive that ware worth looking at. Below are the old forum threads, including responses to the original posts. Here is the full original RF Cafe Forums on Archive.org

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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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Post subject:

Unread postPosted: Mon Jul 18, 2005 12:53 pm

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Joined: Mon Jun 27, 2005 2:02 pm

Posts: 373

Location: Germany

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

Posted  11/12/2012