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|Wideband power amplifeir and input mismatch - RF Cafe Forums|
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Post subject: Wideband power amplifeir and input mismatch Posted: Sat Dec 23, 2006 1:59 am
Joined: Tue Mar 15, 2005 11:43 pm
Hello All :
I have questions regarding wideband power amplifier design (3-stages).
I have a case that the impedance of the device is low in nature, therefore the the response is rather narrow and it is overly sensitive to a little bit of changes.
I read somewhere that to design wideband power amplifier with low impedance, there is a technique called mismatch input matching?
I have tried this, and it is true that when the input return loss is worse, the gain response is wider.
But I am not sure how to relate between wide gain response and input mismatch? Or do I misinterpret this?
Please enlighten me.
Wishing Merry Christmas and Happy Holiday
Jean (Eudyna Devices Asia Singapore)
Post subject: Posted: Sat Jan 13, 2007 12:10 pm
Joined: Mon Jun 27, 2005 2:02 pm
If you consider wideband response as flat gain curve then:
When you match an amplifier to the best return loss then often you will get dips in the return loss which will result in a non-flat gain response curve.
If you will match the amplifier to a higher (bad) return loss than the gain response will become flat and wideband.
From my experience: I once matchd an amplifier for wideband operation (80MHz) and was able to do so only by degrading the input return loss. The return loss still had a reasonable value but less of what I could achieve for narrowband operation.
I hope that I got to the point you meant, if you still have questions please let me know.
Post subject: MismatchPosted: Mon Jan 15, 2007 1:57 am
Joined: Wed Feb 22, 2006 3:51 pm
There are theoretical limits to the bandwidth over which a close match can be achieved in the presence of an irreducible reactance in the load (which means "all real-world situations" !) You can see the books and papers by Herbert Carlin, who did some of the ground-breaking work in the area. (The most recent is "Wideband Circuit Design", the earlier book is "Network Theory"). If they're available to you, there are helpful discussions in the books "Feedback Maximization" by B.J. Lurie, "Network Analysis & Feedback Amplifier Design" by H.W. Bode, and "Wideband Matching" by Chen. These books are probably only available in university libraries, with the exception of Lurie's book, which is published by Artech House under their "In Print Forever" program.
These books will probably tell you more than you really wanted to know about the subject. <grin>
Post subject: Posted: Tue Jan 30, 2007 9:31 pm
Joined: Tue Mar 15, 2005 11:43 pm
Thanks for the advice.