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

Could some RGF/microwave guru on this newsgroup please help ? I am looking at the datasheet for a ONSemi RF transistor, with the S parameters listed for various frequencies. What would be a quick and easy(that I can code as a simple C program) way to convert these to the corresponding Zin and Yout. Thanks in advance for your hints/suggestions.

Reply to
dakupoto
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Why?

Try and find the spice model, and do everything in spice.

One of the remain reasons for stuff like S parameters, was simply that it was easier to measure than other ones in the distant past. Its simply all irrelevant now. We have simulation tools.

S parameters are way too limiting for optimum design. Usually, they are only specified for one or a few current/voltage sets, and they are only useful at all for linear analysis. This is a disaster for decent optimum production design.s

S parameter design for transistor circuits is, essentially, a legacy claptrap rut, that many just can't get out off.

A good spice model will allow you do accurately design over the whole range of operating currents and voltages including the required transient, real world large signals that the circuit is actually being used for.

-- Kevin Aylward

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Reply to
Kevin Aylward

You can do it with a spreadsheet. Checkout Rfcafe.com M

Reply to
makolber

You're obviously not an RF guy. S parameters let you calculate analytically things like the stability boundary, active vs passive regions, maximum available gain, and so on.

Smith charts are super fast and intuitive, as well.

A single analytical result is worth more than a stack of simulations. There are cases that are too hard analytically, but one-transistor microwave amps are not among them.

Cheers

Phil Hobbs

Reply to
pcdhobbs

Sadly, a ton of transistors just don't give that info.

Some don't even give s-params, or their LF equivalents (junction C's, internal resistances, etc.).

The OP wasn't exactly specific...

It's nice to just keep shopping for a part that does, but if this is going deep into the rarefied territory of RF (the OP wasn't exactly specific :) ), you can be SOL very easily.

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

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Curiously, they don't provide the exact formulas relating s-params to the other types of network equations. But between the related articles, it looks that there's enough information to solve for it.

Tim

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Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

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Reply to
JM

On a sunny day (Sat, 6 May 2017 11:24:14 -0500) it happened "Tim Williams" wrote in :

OK, many people had a go... Apart from mutilati I mean simulations, and S parameters that I had to do over and over in school and never used after that, I VERY STRONGLY RECOMMEND JUST BUYING SOME OF THOSE DEVICES, MAKING SOME TEST CIRCUITS, BUILD AN OSCILLATOR, 1 STAGE AMP, ETC, GET THE CURRENT VERSUS VOLTAGE AND DO NOT HAVE FEAR TO KILL ONE ON MORE, GET THE FEEL OF IT.

These days people run simulations, and really they remind me of NASA, in the sense that when NASA detects a new planet, then same day they have an artist impression on their site, sometimes complete with grass, lakes, etc etc.. Von Braun in the sixties build rockets, no computers at that time, he did get US to the moon and back. He KNEW (he and some other German engineers that were captured with him) his stuff. HANDS ON.

It is the same with programming, now people ask: 'Can I do this in Python?' Well don't you think you should at least know the hardware, you know, those little flips and flops, and try some asm, it is actually SIMPLER than Python, more powerful, MUCH more powerful, and several orders of magnitude faster so you can do the same or better in a little micro with kB memory and one core and not your quadcore 4 GHz power slurping monster.

Operating systems and browsers go the same way. [LT]spice is a joke if it comes to real RF, and normal circuits too. it is all about layout, and yes there are programs for that too.

As to NASA, Hollywood makes much better artist impressions, getting so good it is hard to tell what is real and not, not your old puppet show, I was amazed by 'the golden compass' happened to see it on TV, looked it up, indeed a prize winner.

Long time ago, when first transistors came on the market here (1958?) I remember asking one for my birthday. Actually got one, PNP Ge, it died rather soon, but man did I learn a lot.

Hell even if you spice it all and cannot handle the soldering iron to make a test circuit what good is it. And even if your spice works, it may well not in reality. Welcome to the matrix, and now they wonder why they cannot go to mars.

Darth Vader.

PS and sometimes even the things do not meet spec, I remember a specific case of VFET.

AND on top of that, if you have your spice working, you have NOTHING, it is all illusion like that movie, and no planets to walk on. While I have a working prototype device.

It is all illusions I recall, I really don't know tronix at all. In the human neural net, you need that configured, and the ONLY way is practical experience with REAL world stuff. You may have the math to catch the ball, but that does not mean you can play in major league. You may be a top player, but have no clue about physics and math.

Maybe one day we will be able to transfer our neural net weights and configuration to some system, and it would be as smart (or as stupid). Or to others.

Reply to
Jan Panteltje

You're lucky if you get any DC curves. Or capacitances. I wind up measuring that stuff, but it's not enough for a high-speed Spice model.

--
John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

If you know how to use a Smith chart you can design an impedance matching network for same amp in about 5 minutes that would take you the better part of an hour to grunge thru on paper

Reply to
bitrex

Well no shit, Sherlock.

Reply to
Cursitor Doom

So? Just model the strays and parasitics if they're relevant.

Reply to
Cursitor Doom

Sno-o-o-o-ort >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

Forgot to add, "...you can design...", means _somebody_ can, but I seriously doubt that bitrex can. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

I am an analog guy that has run, probably 1 million spice runs. I know what works.

Only if you're pissing about with a kids walki talkie.

Any equation more complicated then v=ir and i=cdv/dt is pretty much useless for design, today. Things are way to optimised now. No one does it it designing analog ASICs for starters, which forms the bulk of the billions of RF units in mobile phones and stuff in the known 3 universes.

S parameters are only valid as a linear approximation, and give incorrect results for stability because of this. They are completely useless for determining distortion, phase noise, or the best operating current for a design, or for dealing with variations. Because, now get this, they are only a linear approximation.

Designing a modern, competitive analog product today, whatever the frequency, requires 10,000s of DC, AC, TRAN and Nonlinear Steady State (PSS) simulations, over temperature, process corners, power supply, and load conditions. This requires accurate spice models, usually VBIC in ic designs.

For example, are you aware that modern RF ASIC TXs are hitting a wall because their power varies slightly as they are powered up. Techniques are needed to dynamically adjust the power supply to keep the output power constant on power up. Its impossible to design those type of circuits without doing extensive simulations in the time domain.

Yeah...

Hardly ever, today. You are obviously not someone that needs to design ASICs, that work first time, and work in their millions.

Small signal analysis has absolutely zero chance of doing that.

Once you know what you are doing, setting up worst case runs and parameter sweeps over 10,000s of transient runs, will achieve what is absolutely impossible to do with manual equations. The world has moved on.

An yes, I know all about manipulating complicated equations.

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And there is no place for them in modern transistor level design. Period. Its a major failing in all the "How to design Analog Circuits" books. They produce these huge equations that are impossible to design with.

Nonsense. Accurate one transistor circuits are not solvable, especially for worst case conditions. Period.

An illustration of this is the effort involved in simply solving for the currents in an ideal transistor with just an emitter resister.

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Now add in capacitances early effect, rb, rc and hfe variation with current. Its a complete non starter.

I await Jim Ts response :-)

-- Kevin Aylward

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Reply to
Kevin Aylward

How do you know what to simulate? Just plunking parts on a screen and running Spice only works for very simple circuits. Try designing a

5-resonator hairpin filter by fiddling.

Analytical techniques, like s-plane analysis, control theory, all that stuff, is sometimes the only way to get a design to analyze. Sure, do the nonlinear analysis, but you need a starting topology.

I just designed a 7-pole elliptical lowpass filter by adding a notch cap to a 1dB Chebychev design. The design came from the Williams book; I managed to fiddle the notch, but I couldn't have possibly fidddled the main filter. (It tried adding a second notch, and it exploded. One notch is apparently my fiddle limit.)

Sounds like 10,000 simulations could be a lot of work.

--
John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

I experienced this year a bad case of a "team" of analog "designers" whose only "skill set" is cutting and pasting from their textbooks :-(

I was trying to demonstrate simplifications and "reductions to spec" when I was cut short by my "malady".

I continued to receive the E-mail trail of their "design" efforts... then I realized they had dumped my contributions and reverted to their textbooks, as I noted really stupid comments about loop compensation and the need for trimming (a simple RRIO OpAmp, fixed unity gain,

4.69K on-chip resistive load, Vdd = 1.8V, GBW = 1MHz).

When I inquired, asking for a schematic update, they cut me off from any further information.

I await the joy when the chip comes out of fab >:-}

SNO-O-O-O-O-ORT >:-}

But, ultimately, ignorance is good for business. I once had a case where I was tossed by an asshole manager (a textbook "designer")... who also refused to authorize my invoices for work already done.

Three years later, with a new manager at the helm, they comes a-begging... "save us Jim".

They not only paid me the outstanding invoices but also paid an outrageous up-front payment to get me to return >:-}

We also have a thread running wild here on S.E.D concerning designing a 2% oscillator (over PVT)... Bwahahahahaha, I think I need another glass of wine >:-} ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
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Reply to
Jim Thompson

The grandparent poster may not have.

So go die in a fire, pal.

Reply to
bitrex

I always liked this comparison:

Sim:

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Gate drive waveform on a "complementary" pair of MOSFETs, driven together (more or less) as one half of an H-bridge.

Measured:

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The blips and stuff are in somewhat different places, and the time skew is a bit mismatched. But it's largely all there, including the sharp splat and the little kinky thing near the end there. (Drool on the right hand side was probably supply bounce, from not modeling the PDN and cap ESR.)

And I made that while I was still at college...

Tim

--
Seven Transistor Labs, LLC 
Electrical Engineering Consultation and Contract Design 
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Reply to
Tim Williams

The technique is have a complete understanding of topological transistor level circuit design. This means have a through understanding of all blocks such as current mirrors, cascades, feedback theory etc... It means having worked out the main simplified equations at some point of the core components, to get a feel of what's important.

That was not the claim.

Nonsense. Complex transistor level circuits must be run on spice in todays modern asic world.

Filter design is a specialised technique that uses specific design tools.

Sure, no one has claimed otherwise.

It look like you don't know how to run a modern spice tool.

Actually, SS has some limited automatic design and placement of filters

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Pardon?

Its trivial to do with modern spice tools, that's why its done that way. Sure, with LTSpice, I agree, its a no hopper.

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The Cadence Virtuoso environment is especially good. You can setup process corners and parameter sweeps in lots of individual setups. Its got great GUI handling of setting up data tests like max/min analysis of anything, like rise fall times, loop phase etc. All measurement for all test runs can be automatically sent to an excel spread sheet etc...

-- Kevin Aylward

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Reply to
Kevin Aylward

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