How to determine Zin, Yout for RF transistor, from A parameters

On a sunny day (Sun, 7 May 2017 20:55:15 +0100) it happened "Kevin Aylward" wrote in :

Really... I does oscillate here, been doing that for decades.

Ah, I am on earth, where are you? ;-)

Good question.

Does it use vacuum tubes?

Very impressive,. -165 dB wonder how you measure that. What do you use it for, QAM 65535? Or QAM 32 bits?

I dunno, I am on earth.

Perhaps. I still doodle on paper before constructing a Spice simulation.

Yep, but see above.

...Jim Thompson

So edifying >:-} ...Jim Thompson

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Thinking outside the box... producing elegant solutions.

"It is not in doing what you like, but in liking what you do that is the secret of happiness." -James Barrie

Well, no, those were photoshopping artifacts actually. I wasn't as good with it back then. :^)

Tim

The "DWIM" switch.

There is a big difference between chip and board level design. The models for board level design are _really_ bad. It's not unusual to find you're breaking several laws of the universe. ;-) Chip level models *have* to be good, or as you point out, nothing will ever work.

If you designed a board with billions of transistors, using only SPICE, I doubt it would work, too.

Halfa megabuck is nothing. We were up to $2M for a full set, ten years ago.

Again, board ASIC

not in my universe

NT

Since no one took the trouble to simply reply to your question, here we go.

The S11 parameter is the input reflection coefficient. It's just a different way to represent input impedance. S11 is in fact what you would measure across the arms of a Wheatstone bridge with the relevant impedance in one of the arms and Z0 = 50 Ohm resistors in all the others. Converting, Zin = Z0*(1+S11)/(1-S11).

The same conversion applies to S22 and Zout. Yout=1/Zout.

Bear in mind that these are linearized parameters of a basically non-linear device at specific bias conditions and with a specific excitation level.

All complex number math, naturally.

Jeroen Belleman

For an unilateral transistor i.e. S12 nonzero, the formulae are a bit more complicated:

Zin = Z0 * ((1+S11)*(1-S22)+S12*S21) / ((1-S11)*(1-S22)-S12*S21) Yout = 1/Z0 * ((1+S11)*(1-S22)+S12*S21) / ((1+S11)*(1+S22)-S12*S21)

One obtains those from signal graph analysis, or (as I did) by copying from Pozar's book.

Regards, Mikko

Does it matter that much? If one's designing say a chain of RF amplifiers, then it would seem the nonlinearity of the final is going to dominate everything, and there are ways of dealing analytically with weakly nonlinear systems.

idk. it sounds a lot like you're saying the only "right" way to design analog RF circuits is to already be an expert analog RF designer. Then you wouldn't need to muss with any math because you would know what to do, intuitively.

I don't know how helpful this advice is for mere mortals.

If you were a _real_ RF design man you'd just know. jeez.

I didn't try to verify in detail, but it looks like there's a error in there, because those expressions do not reduce to mine if one sets S12=0.

Jeroen Belleman

Well, I'll be buying damned few mask sets myself but a half-a-magabuck isn't a lot of money when talking about ASIC or custom chip development. Gate arrays may be significantly less, of course.

It depends on what you are doing.

-- Kevin Aylward

On a sunny day (Sun, 7 May 2017 20:55:15 +0100) it happened "Kevin Aylward" wrote in :

An oscillator, is one that is complete. One that can actually be plugged into another piece of kit.

There are standards. Where is the CMOS or Cliped sine buffer?

And no answer.

That one had one tube in it. Model is AVT150. I have another one, all Transister, MG100. I gave up on the tubes many years ago. Could not be bothered with the weight.

Should have said dBc, but I guess you knowing all about oscillators, would know the standard terminology.

I should expand on this. This is the noise after the limiter/squarer. Raw oscillator designs can be -190dBc to -180dBc. A key point is that this is with an internal 2.5V supply, in a package of 7mmx5mm. Any mere mortal can get that sort of performance in a 1" square with 12V.

Very few applications use a sine wave, so only a final CMOS or CLIPPED Sine output is relevant. Clipped sine don't mean what it says. It means a 1.2V regulated output of various shapes, including square. Its a historic term.

I don't use it for anything. My company sells them to those that do. They are used in various areas such as telecom, gps, adcs, modems, whatever.

-- Kevin Aylward

Yes.

Its everything. The list is endless. Once one part needs an advanced tool, you need to have the advanced tool. Its irrelevant whether over bits may not require it.

Today, all the easy jobs have been done. At one time oscillators only needed stability of 50 ppm. Now some systems requite 1 ppb.

Phase noise is crucial for the vast number of products out there. Its about squashing in 100MBs data for everyone within a 1km radius of each other, and so forth.

If one company is using all the right tools, how do you expect to compete using bear skins and knives?

It is impossible to do modern competitive design using just intuition. Its too complicated. You need to have an understanding as to what to randomly fiddle...

-- Kevin Aylward

My basic point through all of this was to dismiss this general idea of "spice isn't about the real world.... isn't good enough etc...etc..."

Pretty much every modern product today, exists because of the ics in them. All ic design is done in the virtual world. Only a tiny minority of ic designs have any dependence on unknown board level issues.

Sure, I am not an RF specialist. However, I have done a few bits and bobs at the several GHz region. I have also spoken to RF specialists. Most have missed the boat. They think in ways passed on from their fore fathers, that were passed down from their forefathers.

The days of graphical techniques and manual equation solving are gone. Whether its electronics, designing the same bloody energy efficient car body shape, trading stocks and shares, its all done by running millions of simulations. It what TFlop computers are very good at. You just need to learn how to drive them correctly. Unfortunatly, as far a board level spice users go, most don't know how.

-- Kevin Aylward

Hey, I still use slide rules! Best way to set up a resistor ratio while rummaging through the stock drawers for a suitable pair to build the divider.

And a good log-log chart or nomograph is still useful (just hard to explain to a millenial).

The digital age has all the advantages of a digital watch, and none of the advantages of a clock dial.

I guess if your gig is doing designs that are intended to be sold in their bazillions, then yeah, it's extremely important to know everything about everything. Because, well, that's the gig you're in. If you know that your way is the only way that works in that gig then I can hardly argue because hey, that's your gig, not mine. ;-)

Not doing it whatever way that is is probably OK if you're in a different gig. Sometimes all you need is an RF amp that's good enough and it doesn't matter if anyone wants to buy them in quantities of millions. Unless every structure that could possibly ever be needed by anyone has already been produced in IC form by someone who can do it better. Maybe that's the case. Seems that way sometimes.

"Can't get a job without experience, can't get experience without a job."