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Old 9th Jan 2022, 6:54 am   #1
dmowziz
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Default s2p file from VNA

Hi...

Want to learn more with Genesys simulator using small signal s parameters (s2p)

Please how do I measure this on a real transistor (maybe using a NanoVna) and get the s2p file?

Thank you very much!
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Old 9th Jan 2022, 5:24 pm   #2
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Default Re: s2p file from VNA

I don't use Genesys, but these links may help

https://nanovna.com/?page_id=90

https://ac6la.com/zplots1.html
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Old 9th Jan 2022, 8:43 pm   #3
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Default Re: s2p file from VNA

Quote:
Originally Posted by Cruisin Marine View Post
I don't use Genesys, but these links may help

https://nanovna.com/?page_id=90

https://ac6la.com/zplots1.html

Thank youuu.. I did search but didn't see these

But now, measuring it... Have been searching online but maybe I need to search more

Thanks
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Old 10th Jan 2022, 2:23 am   #4
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Default Re: s2p file from VNA

Please, To get S Parameters of a transistor on the bench (Common Emitter mode), do I bias it like this?

data from 1 MHz

Thank you
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Old 10th Jan 2022, 12:43 pm   #5
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Default Re: s2p file from VNA

What's your upper frequency limit?

The transistor needs to have the emitter solidly ac grounded over the entire frequency range of interest, with minimum series inductance. For 1MHz that means something around 0.47uF or larger, in chip or disc format.

Normally you'd expect to see a broadband choke in place of the 1k2 resistor in the collector: that would allow better control of the collector voltage.
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Old 10th Jan 2022, 1:04 pm   #6
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Default Re: s2p file from VNA

Quote:
Originally Posted by John_BS View Post
What's your upper frequency limit?

The transistor needs to have the emitter solidly ac grounded over the entire frequency range of interest, with minimum series inductance. For 1MHz that means something around 0.47uF or larger, in chip or disc format.

Normally you'd expect to see a broadband choke in place of the 1k2 resistor in the collector: that would allow better control of the collector voltage.
John
I see... Thank you John

300 MHz....
500 KHz to 300 MHz
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Old 10th Jan 2022, 1:51 pm   #7
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Default Re: s2p file from VNA

I'm currently on my lunch break so can only offer a few tips.

The first one is to be careful if you are using a nanovna. The ports of the nanovna are not AC coupled so you can easily damage the tiny bridge resistors inside the nanovna with external DC.

Ideally you want to be measuring all four s-parameters s11 s21 s12 s22 and the nanovna is only a TR VNA. So you would have to be able to swap the test fixture around to get s22 and s12.

Also, this is usually done with a VNA using bias tees as in the setup below. The only thing inside the test fixture is the transistor itself, no resistors or chokes should be inside the reference planes. Your nanovna would have to be protected from DC if you wanted to try this.

I've done this stuff many hundreds of times at work or here at home and it does involve a lot of preparation in terms of correcting the test fixture to set the reference plane right at the pins/pads of the transistor under test.

It also means setting the correct RF drive level to prevent overload. Your BJT looks to be biased at several mA. This will mean that s21 could show +25dB gain at low frequencies when the BJT is configured in a regular 50 ohm test fixture like the one below.

It's probably better to ask on the nanovna forum about nanovna related stuff like this because there will be few nanovna users on here and even fewer (if any) that will have measured a BJT like this.
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Old 10th Jan 2022, 2:02 pm   #8
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Default Re: s2p file from VNA

My advice would be to try measuring a process 50 JFET first (eg BF256B, 2N3819 2N4416) as the transconductance is much lower compared to a BJT. I don't know how low the RF source power can go on some nanovna models but a JFET will probably measure out OK even with the relatively high source power from the nanovna. I don't think the JFET or the nanovna will be over-driven even with the process 50 JFET in common source.
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Old 10th Jan 2022, 2:43 pm   #9
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Default Re: s2p file from VNA

Quote:
Originally Posted by G0HZU_JMR View Post

I've done this stuff many hundreds of times at work or here at home and it does involve a lot of preparation in terms of correcting the test fixture to set the reference plane right at the pins/pads of the transistor under test.
Thank you very much

But don't understand what you mean by reference plane... Please what do you mean?
I'm using thru hole components : the image below is the initial setup I had (JFET)

I'll use that setup above

Maybe when you're free, kindly post the s parameter data of a 2N3904 or MPSH10 at any bias and frequency range. Let me measure and compare


Thanks Jeremy

Last edited by dmowziz; 10th Jan 2022 at 2:51 pm.
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Old 10th Jan 2022, 2:52 pm   #10
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Default Re: s2p file from VNA

This...

and about the NanoVna, when I get longer SMA leads and (N to SMA) connectors, will be using a VNA (but it still only measures s11 and s21 at once)
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Old 10th Jan 2022, 7:12 pm   #11
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Default Re: s2p file from VNA

Quote:
Originally Posted by G0HZU_JMR View Post

I used that setup (to get 5mA), R1 = 62k... 1mH inductors..100 nF

The s21 is not above 1 dB

Assist please

I'll join the NanoVna forum
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Old 10th Jan 2022, 7:53 pm   #12
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Default Re: s2p file from VNA

What you are trying to do is really quite advanced. I suspect few people on the nanovna user group forum will have done this.

Ideally, the s-parameters would be measured by a theoretical VNA that was tiny enough to sit on the pins of the transistor as in the image below. The port impedance of the VNA would be a perfect 50 ohms and it would also be able to bias the transistor at (say) 10Vce and 5mA before taking any measurements.

In the real world the VNA ports won't be a perfect 50hms and the VNA ports are a long way from the pins of the transistor. So the VNA has to be calibrated and also there will have to be some corrections added to try and achieve the equivalent of what is shown in the image below. This isn't easy to do if you want good results up into UHF.

Genesys does have some s2p data bundled with it so see below for a really old s2p file of a MMBTH10 at 10Vce and 5mA Ic that came free with Genesys. This is the SMD version of the MPSH10.

This s2p file was measured by Philips the manufacturer back in 1990. It covers 40MHz to 1000MHz. For something like a MMBTH10 I would normally measure it up to about 3GHz to make sure I've measured across all frequencies where it could go unstable. However, the manufacturers rarely measure their devices like this.
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Old 10th Jan 2022, 7:59 pm   #13
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Default Re: s2p file from VNA

Quote:
Originally Posted by G0HZU_JMR View Post
What you are trying to do is really quite advanced. I suspect few people on the nanovna user group forum will have done this.

.
Thanks Jeremy, I think you can make me get it right...

Please firstly, can I see a setup you use to measure? (Im using thru hole right now.. you use smd.. Just to see for the future)

I'm redoing it now but tried the bias tee image above, couldn't get above 1dB

Thankssss
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Old 10th Jan 2022, 9:00 pm   #14
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Default Re: s2p file from VNA

I think you may be trying to run before you can walk, you need to first of all master the common emitter amplifier and see how it behaves (especially at RF). It would be much more beneficial to measure the performance with an RF Millivolt meter, that way you won't be doing any damage to your VNA.

There are plenty of sites with information on common emitter design that can be easily found.
There may well be sites with designs for RF Millivoltmeters, or even low power RF power meters.
I would save the VNA experiments for later, once you have firmly got your head around every aspect of the common emitter amplifier and its design and importantly layout.

Even after all these years, I normally turn to my RF mV Meter before going on to looking at it on a Spectrum analyser, always making absolutely certain I can cause ZERO damage to the SA.
Rarely do I use the VNA to confirm things, they can very easily be damaged.
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Old 10th Jan 2022, 9:16 pm   #15
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Default Re: s2p file from VNA

Quote:
can I see a setup you use to measure?
I'm using a fairly modern Agilent VNA and Ecal system and an SMD test fixture that is good to many GHz. The VNA can vary the source power down to something like -55dBm. I can't show you the exotic SMD test fixture I use because it is something developed at work over many years for doing stuff like this. However, you only need a basic test fixture anyway.

Quote:
I used that setup (to get 5mA), R1 = 62k... 1mH inductors..100 nF
The s21 is not above 1 dB
Assist please
The nanovna has limited signal handling capability on the second port and at 5mA the BJT will probably have 23dB gain at low frequencies in a typical VNA test fixture. Therefore I'd expect to see the nanovna become overloaded so it will only show a small gain for s21 due to the significant compression that would occur if you test a device with 23dB gain.

My advice would be to ask on the nanovna forum. There may be some nanovna models that can turn down the source power to a really low level and yours might be one of them. You could use an attenuator to do this but it will limit what you can measure in terms of s11.
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Old 10th Jan 2022, 9:49 pm   #16
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Default Re: s2p file from VNA

Quote:
Originally Posted by G0HZU_JMR View Post
The nanovna has limited signal handling capability on the second port and at 5mA the BJT will probably have 23dB gain at low frequencies in a typical VNA test fixture. Therefore I'd expect to see the nanovna become overloaded so it will only show a small gain for s21 due to the significant compression that would occur if you test a device with 23dB gain.

My advice would be to ask on the nanovna forum. There may be some nanovna models that can turn down the source power to a really low level and yours might be one of them. You could use an attenuator to do this but it will limit what you can measure in terms of s11.
Thankss... I'll retry when there's N to SMA connectors available and ask again here if anything..
Thank you Jeremy




Quote:
Originally Posted by Cruisin Marine View Post
you need to first of all master the common emitter amplifier and see how it behaves (especially at RF).
Thanks, maybe you are right but please how do you mean? Common emitter amplifier at RF, to predict the behaviour, don't one need to know the capacitances (Base to collector, BE)
Unless using maybe resistive feedback (Shunt and series), can predict S21 and S11..

The S parameters data I need is to learn with a simulator and actually to design oscillators not an amplifier.

But please how will you go about knowing how the transistor behaves at RF?
I searched before how to measure these capacitances, didn't find.

Thanksss

Last edited by dmowziz; 10th Jan 2022 at 10:08 pm.
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Old 10th Jan 2022, 11:53 pm   #17
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Default Re: s2p file from VNA

Thanks, maybe you are right but please how do you mean? Common emitter amplifier at RF, to predict the behaviour, don't one need to know the capacitances (Base to collector, BE)
Unless using maybe resistive feedback (Shunt and series), can predict S21 and S11..

The S parameters data I need is to learn with a simulator and actually to design oscillators not an amplifier.

But please how will you go about knowing how the transistor behaves at RF?
I searched before how to measure these capacitances, didn't find.


You will soon find out that trying to ascertain what these values in an Oscillator may well drive you potty.
Oscillators can lead you down the garden path, down the country lane and eventually leave you stranded on a raft in the middle of the Atlantic.

Sometimes intelligent assumption based on changes around the device lead to a better understanding of how the device works, coupled with the best data sheets you can find etc.
If the data sheets you can find, are not good enough for the device, try to get good data sheets for another device. Some of the old Motorola data sheets are very good.

Oscillator's are a complete b**ch, they really are.

Good luck anyway, you are a braver man than I, Gunga Din!

Last edited by Cruisin Marine; 11th Jan 2022 at 12:00 am.
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Old 11th Jan 2022, 1:02 am   #18
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Default Re: s2p file from VNA

Some time ago you asked about 'reference planes' after Jeremy mentioned them. Without this understanding, results coming from your VNA will be meaningless.

The connection from your VNA to your DUT will involve various lengths of transmission line, be it coax, microstrip or whatever, and several connectors/adaptors. Let's keep it simple and say it is all 50 Ohms, and well matched.

Your DUT when measured for s11 will present some sort of impedance on its die, and will create a reflection. The VNA measures the reflection in magnitude and phase so it can compute the impedance for you..... but whoah! there is a mismatched transmission line involved. If I measure the voltage and current on that line, I find the phases of the forward and reflected waves change depending on where along the line I look, so the impedance is different. On a Smith chart, the impedance goes round and round a circle.

A basic VNA measures the impedance seen at its terminals. But you want the impedance at your DUT's terminals!

The WHERE of the impedance measurement (and alsofor the phase of transmissionmeasurements) are referred to as the reference plane.

You can measure all your fittings and correct for different reference planes mathematically. Or you can calibrate your VNA not at its own terminals, but at the place of interest on your fixture, and the resulting cal now works at that reference plane.

It's complicated, but unless you understand and are comfortable with it, you may get results, but not the right ones.

To work in this area you need to be comfortable with transmission lines and Smith Charts.

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Old 12th Jan 2022, 1:58 pm   #19
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Default Re: s2p file from VNA

Quote:
Originally Posted by Radio Wrangler View Post



A basic VNA measures the impedance seen at its terminals. But you want the impedance at your DUT's terminals!

The WHERE of the impedance measurement (and alsofor the phase of transmissionmeasurements) are referred to as the reference plane.


You can measure all your fittings and correct for different reference planes mathematically. Or you can calibrate your VNA not at its own terminals, but at the place of interest on your fixture, and the resulting cal now works at that reference plane.

DAvid
Thanksss, I get it now.

Actually saw a similar circuit Jeremy provided in Microwave transistor amplifiers book by G Gonzalez

Thanks for the explanation
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Old 12th Jan 2022, 6:14 pm   #20
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Default Re: s2p file from VNA

I dug out a bag of OnSemi MMBTH10 BJTs (purchased from Farnell with part number 2454030) and measured the s-parameter data on my VNA to compare with the Philips s2p data for the same transistor type at 10Vce and 5mA Ic.

See the plot below. This shows good agreement for GMAX and K factor although the Philips data only covers 40MHz to 1000MHz. I measured from LF through to 3GHz on my VNA to look for potential instability issues up above 1GHz.

You can see from my data (the darker blue trace) that the K factor dips back below 1 up around 2GHz (marker 4b) and this shows that the MMBTH10 can go unstable and oscillate up at about 2.4GHz if the circuit layout permits this.

The agreement below is quite good considering these measurements have been made 32 years apart and one MMBTH10 device was made by Philips and the other by OnSemi. The MMBTH10 is the SMD version of the MPSH10 BJT. These transistors typically have an Ft in the region of 650MHz to 800MHz and command much greater care and understanding in terms of circuit layout to prevent unwanted oscillations up in the 2GHz region.
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