[AMPS] Conjugate Matching In Class B and C Amplifiers

Billy Ward billydeanward@hotmail.com
Wed, 16 May 2001 14:51:58 -0000

>From: Jon Ogden <na9d@speakeasy.net>
>To: Billy Ward <billydeanward@hotmail.com>, Amps Reflector 
>Subject: Re: [AMPS] Conjugate Matching In Class B and C Amplifiers
>Date: Tue, 15 May 2001 22:42:57 -0500
>on 5/15/01 4:45 PM, Billy Ward at billydeanward@hotmail.com wrote:
> > Linear Amplifiers may or may not be conjugately matched. For maximum 
> > transfer to occur both in and out, and for the amplifier to be
> > unconditionally stable, there must be a simultaneous conjugate match.
> > This is not always easy as the input match affects the input match and 
> > versa. However, it CAN be done.

>Conjugate matching is not required for unconditional stability.    That's 
>incorrect.  Many low noise amplifiers are purposely mismatched because 
>simultaneous conjugate match generally does not equal minimum noise figure.

I was not taking minimum noise figure into the context of what I said.  I am 
willing to learn.  I purposely mismatch for best noise figure. in low-level 
stages, also. However, I am curious how that makes my statement incorrect 
that Conjugate Matching is not required for unconditional stability.

>Unconditional stability is determined by K factor of Linville's theorem (if
I remember the name correctly, it's been a while.).

I, also, do not remember the theorem name but it sounds correct.
>Additionally, adjusting input match does not necessarily always affect the 
>output match and vice versa.  I am trying to think whether or not your 
>statement is correct.  Too many cobwebs upstairs right now.

Well, I came in on this thread late and my statement was referring to power 
circuits and it may not apply in low-level but I have spent my life in power 
design and manufacture.
>Generally speaking of this subject, I had always thought that the 
>efficiency of an amplifier and whether or not you simulataneously match it 
>were independent.  It wasn't until coming onto this reflector and reading 
>stuff from the likes of Dick Erhorn that some people feel that a conjugate 
>match guarantees 50% efficiency or less.

I haven't read after Dick Erhorn as I am on four reflectors and don't get to 
read everything but if he is teaching along this line I will pay more 

However, The power transfer arrived at by the Conjugate Match is most easily 
proven by understanding the standard POWER THEORUM which states that maximum 
power transfer will occur when the resistance of the load is equal to the 
resistance of the driver.  Then carry that further by realizing that when 
the impedance of the driver is equal in value but of the opposite sign to 
that of the load, it is, of course, cancelled leaving only the real part. I 
realize that you have had a good grasp of resonance for many years with your 
experience, but some folks over look the fact that when resonance occurs, it 
brings us back to the standard POWER THEORUM, so looking at a voltage 
divider which has equal resistances leaves half of the power across each 
resistive element which equates to 50% efficiency.

>Of course, since my schooling and most of my work life revolved around 
>A amplifiers, I never thought about efficiency anyhow, since it's poopy in 
>class A amp anyhow.
>So some people here showed me the view on efficiency being 50% or less; I
>stated it in an earlier post; Tom Rauch says that is incorrect.  I haven't
>had the time to go back to my textbooks and look at what they say.
>Jon Ogden
>NA9D (ex: KE9NA)
>"A life lived in fear is a life half lived."

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