Nice. Exactly: "what it wants to see" is perfect. Of course, "varying the load" requires load pull test equipment and that can be expensive. When load pull equipment is not available, we're stuck with other methodology. In that case, my first order cut is the AC load line, a harmonic short at the device, and enough flexibility in the layout to pull it in by cut and try. I haven't used ADS or Microwave Office's Harmonic Balance simulators. I suppose with good behavioral models and a good simulator, a good deal of cut and try could be circumvented.
Obviously people don't have 100 W (or more!) network analyzers looking into the output and pretending the device is similar to a linear small signal device.
Don't know. Whatever mismatch there is, at whatever moment in time, it simply results in reflection back towards the load. Reflections could also cause additional non-linearity in the PA. Therefore reflections for higher powered PA's are directed off to a dummy load via a circulator.
They say that 1/2 of all advertising money is just wasted. The problem is no-one can say which half.
Besides the advertisers don't care about the value of what is sent. They only care about the wallet of those who are listening.
How do you arrive at that? FCC rules don't specify the nature of the music programming, really. If the "music" always has the modulation index at least 30% with rap, the dynamic range actually needed is much less than for something from BareNakedLadys
And so it remains with additional elaborations not quoted here.
Seeming is a rather insubstantial thing to hang your theories on.
And this reveals the error of "Seeming" because the so-called meaning you ascribe is this same nonsense. Pay more attention to reading instead of writing. It has been pointed out more than once, and by several, that Matching comes under many headings. The most frequent violation is the mixing of concepts and specifications (your text is littered with such clashes).
And I preserved this clash quoted above as an example. If there is any misapplication, you brought it to the table with this forced presumption. The misapplication of S parameters to a large signal amplifier is one thing, to project this error backwards into the fictive theory that there is some difference between large and small signal BEHAVIOR (not modeling) is tailoring the argument to suit a poorly framed thesis.
None of your dissertation reveals any practical substantiation, hence it falls into the realm of armchair theory. We get plenty of that embroidered with photonic wave theory that is far more amusing.
You entirely missed the point. You don't know the output impedance because you don't have a way of determining it by swinging the output full-scale. Even for class A, large signals will/can have rail to rail swing. The device will not be linear for large swings: sinusoidal input swing will not result in a sinusoidal output swing. But "impedance" is a sinusoidal (s-domain) concept. So how can you define an impedance--a sinusoidal concept--when the waveform is not sinusoidal for an inputted sine wave? The point is that the output impedance is time dependent ("causes" the non-sinusoid output for sinusoid drive), which rather makes the concept questionable. As I wrote earlier, one might decide to consider a time averaged impedance, but I'm not clear on what the utility would be.
There is no "presumption." Linear parameters and theorems totally ignore practical limitations--this is a fact and you can look it up in just about any text on circuit analysis. The simple linear model is perfectly okay for small signal devices. It isn't okay for large signal devices. In any case, load pull equipment does not make the pretense of defining output impedance of an active large signal device. It does say what the load needs to be to acquire maximum power out of the device.
No, it isn't. Thevenins and conjugate matching (for maximum power transfer) are explicitly linear small signal device models. Their use in RF PA output design is a misapplication.
We're talking about one of them. Misapplying small signal linear parameters to the output of a large signal device.
Who are you quoting and why?
Any definition won't do, and for this discussion the specific "won't do" is using conjugate matching which is a small signal (linear) model.
Hey, at least you're recognizing that DC power is important. Where in conjugate matching ideas or Thevenins theorem do you see any concern of DC power? That's right, you don't because they a simple small signal models where DC power and voltage have no bearing because the signals are so small, relatively speaking.
*You* brought up Thevenins and armchair philosophy regarding it, not me. I said Thevenins was irrelevent, and now you appear to agree with me. Ken effectively brought up conjugate matching, not me. The original comment I was challenging was:
"...the antenna works as an impedance mathcing network that matches the output stages impedance to the radiation resistance."
I simply wanted to make it clear that the "matching" done was not an issue of "output impedance" per se. It is an issue of how the transistor is to be loaded to extract maximum ouput power.
Exactly. It is about DC to RF efficiency, as I've been pointing out since my first post, and which you initially commented was "nonsense" but now seem to agree with. "Impedance matching" meant in the normal sense of conjugate matching for maximum transfer of power is a misapplied small signal concept/model. I think that is all I've really been saying.
This goes >You don't know the output impedance because you
This is more properly an admission from you, than a projected inability upon us. You may not know how, but this does not prevent me from expressing a value that is suitably accurate.
Now, within the field of measurement, no statement is accurate without an expression of its range of error. However, in this regard accuracy is still a remote issue as you offer nothing of practical consideration and have failed to respond to a simple example to provide context.
Richard Harrison, , KB5WZI, has in this sense already done the heavy lifting with:
continuing....
This marks an artificial imposition not required to respond to the spirit of the topic. Such swings are not necessary.
This is immaterial to impedance and is a set-up of another artificial imposition: the Thevenin Model (which was specifically dismissed). Hence we are into a cascade of impositions.
This is baloney cut thick. S Domains (?) are at best a modern contrivance to model well behaved small signal devices. Their utility follow theory, they do not drive theory.
There are no sine waves in nature, so by this contortion of logic from above there are no s-domains (?). Why are there no sine waves in nature? Because nature is bounded by the Big Bang (a discontinuity) at one end, and has yet to fulfill its infinite extent.
In other words, tedious appeals to artificial impositions of purity fail at the gate for their sheer collapse of internal logic. This kind of stuff appeals to arm-chair theorists who find themselves impotent to perform.
Classic performance anxiety. Engineers learn to live with limitation and to express results and sources of error so that others can judge merit. Priests are better suited with mulling over these issues of ambiguity.
Knowledge limited. There are many suitable texts that offer a wider spectrum of discussion that are fully capable of answering these issues. However, it is made worse that most of this stuff is derivable from first principles and no recourse to vaster libraries is actually needed.
And yet there is no substantive illustration to prove this ambiguous point. What constitutes small, and what demarcates large? Such nebulous thinking clouds the obvious observation that the full range of devices themselves operate on only one principle. What is limited is the human component of their perception, not the physical reality of their operation. The faulty choice of models (S Parameters) is not the fault of either Physics or the devices when they diverge from the crutch of calculation against the wrong mathematical expression.
This is simply the statement from a lack of experience.
These statements are drawn from thin air.
Given the failure to provide any discussion for either or any form of matching suggests a lack fluency in any of them.
I rejected it as an unnecessary filigree, but I notice in the quotes above that you readily embraced it as a necessary imposition.
This compounded with the denial of Thevenin is quickly closing the available matching mechanisms. If it is not about Thevenin, and it is not about Conjugation, then I am willing to wait to hear what it IS about.
....But not really. I have little faith that the difference is appreciated nor how many ways a match may be accomplished or for what ends.
I am always suspicious of how a quoted claim is couched by the rebutter (cut and paste from the original is always available and citing the link to the complete contextual post is hardly Herculean). However, responding to the bald statement, I find nothing objectionable about it.
Again, a presumption not brought to the table. It may follow as a consequence, but it is not a necessary condition.
Our questioner who started this thread is undoubtedly interested in the outcome in terms of maximum radiation for a limited power - it is a chain of causality that is a forced step matching issue from the battery to the æther. This is a first principle of successful production engineering.
You don't have to swing the output full-scale to measure the impedance. Any change in the load, no matter how small, will cause a change in the output voltage and the output current. From these you can calculate the output impedance at the current operating point.
When a transistor is operating under large signal conditions into a tuned load, there is still an output impedance and this impedance still discribes what will happen for small changes in the load.
This incremental impedance is one of several different impedances that can be defined for a non-linear source. No one is more valid conceptually than another, but some are of more practical significance than others.
The point is that if you want to talk/write about one of these impedances, you need, to prevent misunderstanding, use a precise term, such as 'incremental output source impedance' and define it.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
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One would think that a 12 billion year windowing would be close enough. :-)
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From seeming to appearances - leaps of faith are better suited for debate at the Vatican.
The remainder, unquoted due to repetition of the same basic errors, has already been commented upon in another posting. Oh, except the more entertaining jousts:
Mmm-hmm :-)
To be so eagerly embraced as a fellow fool! Something of the chess equivalent of the sacrificial queen gambit.
As I've noted in the past, you can fill a library with negative assertions without ever offering an answer, eg.:
The list could go on, be completely accurate, and yet never actually mean anything in the end much as the nonsense you offered from the start.
You sighed with content at being offered a "relevent question/statement" Your re-iterative response contains the same (how could it be otherwise?) slack of precision that started this. Want to try again?
You could have as easily expressed what sense they ARE matched, but instead this time offer what Basis of Matching you are attempting to describe. This is the more rigorous approach that eliminates vague descriptions and uses standard terms. If you have to query about what "Basis" means (used by professionals - namely metrologists who can quantify Output Z of all sources) - then we can skip it as a topic out of the reach of amateur discussion.
Note:
Does not qualify as a Basis. It is suggestive of one, but because you indiscriminately mix several Basis within your discussions, it is your responsibility to be precise. If you can accomplish this, then we can proceed to review how little it all matters.
Barring resolving any of these issues of precise language, I notice that you rather enjoy fruitless jousting with them than challenging my support of Ken's (supposed) statement that you say is your focus:
Not only that, but since by definition the Universe started at T=0, any 'sine wave' that starts at a positive zero-crossing is at any later time indistinguishable from a real one that started at T=0.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
LOL. Sure, the purpose of a power amp is to actually extract power. This is a good start.
Perhaps a simplistic (and of course idealized) class A example would help. And I want to remind that this is a simplification of the first order design cut.
The first assumption/idealization for the class A example would be to demarcate between strong and weak non-linearity. This demarcation is basically the boundary of clipping, both positive and negative. That is, we want our class A amp to swing to the rails but not go beyond. In our class A design we will accept weak non-linearity but not strong non-linearity.
Lets say we have selected a class A device/amplifier for which we can statically dissipate 10W. The drain DC circuit is simply an RF choke (see, it is a simple example!). Let's say the quiescent values are a 10 V supply and 1 A of current (10 W). The question is: how do we load the device to extract maximum power given the "no clipping" (strong non-linearity) constraint?
Say we load it with 20 ohms, what happens? The max positive swing before clipping is Id*rL = 1*20 = 20 V. The max negative swing is, of course, Vd = 10 V. Since the 10 V is the lesser of the two swings, our non-clipping design constraint limits us to 20 Vp-p. So we can deliver (Vp)^2/(2*rL) = (10)^2/(2*20) = 2.5 W.
Say we load it with 5 ohms, what happens? The max positive swing before clipping is Id*rL = 1*5 = 5 V. The max negative swing is, of course, Vd = 10 V. Since the 5 V is the lesser of the two swings, our non-clipping design constraint limits us to 10 Vp-p. So we can deliver (Vp)^2/(2*rL) = (5)^2/(2*5) = 2.5 W.
Say we load it with 10 ohms, what happens? The max positive swing before clipping is Id*rL = 1*10 = 10 V. The max negative swing is, of course, Vd = 10 V. Since they are equal, we get 20 V of p-p swing. So we can deliver (Vp)^2/(2*rL) = (10)^2/(2*10) = 5 W.
Our circuit loaded with 10 ohms delivers twice as much power as with the lesser
5 ohms or greater 20 ohms. That is, extracted output power is peaking at some finite non-zero value. This is also easily seen to be most efficient point for this simplistic example.
In no way was the ouput-Z of the amplifier considered in deciding how to load it for the purpose of extracting maximum power from the circuit. The output-R is completely irrelevent.
This example is intended to be illustrative rather than exact.
Yes, I already noted that for that portion of the impedance, it should be tuned out *as best* possible.
"...(to be fair, the time-averaged reactive output component is tuned out as best possible)."
Well they are apparently your's too! Your own example of testing your own PA said absolutely zip about output-Z. The most you could say is how the circuit is loaded and its RF/DC efficiency. You're agreeing with me and can't even seem to recognize it.
Here's the original quote [Ken]:
"When the correct matching is done, the antenna works as an impedance mathcing network that matches the output stages impedance to the radiation resistance."
He brought up "matching to the output impedance" (of the device), not me. There is no "misinterpretation of meaning" when it comes to making statements about matching output impedance to a load impedance. The meaning is well-understood and precise. It means conjugate matching for maximum power transfer, and this is explicitly sourced from small signal theory. Small signal theory is oblivious to practical factors like supply rails and efficiency. These practical factors are paramount in PA design. Thus to apply a theory that ignores paramount factors is to beg a design which will likely be non-optimal.
I'm paying attention, you agree with me but don't have the background to understand it.
No, you still don't get it. I don't have a problem with saying it is "matched." For example, I said a PA needs to be "load-line matched." This has a specific meaning, and that meaning explicitly isn't "impedanced matched," which means something else. If you don't bother to know what the words mean, I might as well speak Swahili.
There is no forced presumption. The words have explicit definitions. If you don't know the language, you have no way of communicating.
The models come from behavior and/or device physics, and were developed for the express purpose of efficient design methodology. Small signal models can (and do) conveniently ignore large signal concerns such as efficiency and supply rails, because such concerns are irrelevent in the small signal milieu. To apply a model to a milieu for which the model is not suited begs a non-optimal design. The output-impedance concept itself is quite dubious for large signal amplifiers.
I read in sci.electronics.design that gwhite wrote (in ) about '1/4 vs 1/2 wavelength antenna', on Wed, 2 Mar 2005:
Good idea! Furahini mkaimbe. The wrangling is getting tiresome.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Efficiency seems to be important enough to mention.
No one said they "are necessary." But not driving "as hard as possible" simply means you are wasting power and paying for a bigger device than you need to.
sinusoidal
Oh? The definition of impedance is:
Z = V/I
V and I are sinusoid (phasors), *by definition*. It is as if you don't know the definition of impedance.
S-domain *is* linear circuit theory.
It *is* linear circuit theory. The theory was developed for its utility.
formatting link
What are you talking about? No circuit is perfectly linear, and no one I knows claims such. That does not invalidate linear theory, nor denigrate its utility properly applied. Many circuits are "sufficiently linear," and "care" little about supply rails and efficiency.
I'm not religious, but you beg me.
Ohmigod!
Suit yourself. Go ahead and apply theory to that for which it was not designed to handle. In fact, you don't do it -- your own example about testing your PA stated absolutely nothing about linear theory, or output impedance of the device. I use (apply) linear theory a good share of the time. That doesn't mean I don't recognize its limitations as a theory (a model).
to
would
Wow. More importantly, engineers select appropriate models for the design task. They don't bother with ones that have no application to the task at hand.
Yeah, like for example:
formatting link
Yes, load line matching is certainly a first principle.
Maybe you didn't read those first principles quite closely enough. Nor have you read this thread well. Large signal amplifiers -- i.e. power amplifiers -- "care" about DC to RF efficiency and supply rails. Small signal amplifiers don't "care" about that.
Quite afraid to ask, but being brave, I ask: what "one principle" is it "that the full range of devices themselves operate" upon?
And you critiqued me for nonsense.
And no one said so.
No, it is a fact of the matter. You don't know what the equipment does.
design
No, for PA design, the thevenin impedance of the output source never enters "the equation." Thus pretending that it "is there" is an unfounded assertion. You asserted thevenins to PA design, now prove it. You can't.
What utter ignorance of what has actually been written. In my very first post I described the first order cut of matching technique.
Exactly. It is not necessary. But you brought it up, and Ken implied a simile with "impedance matching." You might wonder why it is not necessary. You might even ask the question wondering if the reason it never shows up is because it would be a misapplication of the concept.
effectively
Ah, at last a relevent question/statement. See my first post in this thread.
You don't appreciate it because you don't understand it. That's not my problem.
If you don't know what the end is for an RF PA, how could you hope to scratch a meaningful and optimal solution?
LOL. I guess you don't appreciate convenience.
That's because you don't understand the difference between impedance matching and ac load line matching.
loaded
It was brought to the table in my first post to this thread.
How would you know about first principles of production engineering and what does it have to do with this thread?
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
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