Really, RF parts aren't all that repeatable. Mini-Circuits (and others) change fabs now and then, without warning. Lots of RF parts don't have min/max specs anyhow.
And, no offense intended, RF is fairly fuzzy anyhow. People measure in dBs, not per cents or PPMs.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
:
ng
to
to
y
ings on either S21 or S11. Is this several degrees of phase error something that is important to you? If not then move on.
tion measurements that critical?
Actually, Rf parts in the .500-2GHz are very stable (repeatable) and solid these days. remarkably so. There are so many functions built into parts t oo....for instance, amplifiers are all biased up and matched to 50 ohms. It would be curious to know what he is actually trying to measure to determin e if this little bit of phase slide into an open circuit would make any dif ference or not.
If he is just doing S21 measurements on an amplifier I doubt it matters. I f he needs to know this for some reflective oscillator application then the measurement is going to be trumped by his empirical results.
AFAIK, the overwhelming majority of S11 measurements are not concerned with phase. S21 certainly is, though.
ISTR that the later HP VNAs certainly did this and also 'recognised' when the cal kit being used was one of theirs or not. If it *did* turn out to be one of theirs, then the accuracy was noticeably better.
I use MMICs as wideband pulse amplifiers and TDR them to see the equivalent input impedance. 50 ohm parts might be 38, might be 65.
The newer self-biasing MMICs have very strange internal bias loops.
Power parts, on their data sheets, usually say "adjust the DC bias trimpot until it works." I have to do my own DC measurements.
I asked MiniCircuits if one of their MMICs inverted the signal or not. They didn't know.
Of course, Darlington mmics invert.
Am 17.11.20 um 01:24 schrieb John Larkin:
No. You did not know what to ask. The question makes no sense.
You are thinking DC. You were given the S-parameters but were unable to interpret.
Gerhard
-- Science teaches us to trust. - sw
No, I was just trying to see if the MiniCircuits engineer understood the part.
I work in time, not phase.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
not.
-- Science teaches us to trust. - sw
Am 16.11.20 um 17:48 schrieb Brent Locher:
This here is an amplifier made by a regular of s.e.d. who is currently badly missed. <
The amplifier is potentially unstable. Between 100 KHz and 50 MHz, the real part of the input impedance is negative. The rest of the input impedance is a small capacitor. If you connect anything inductive to the input, the amplifier will oscillate. The measured phase angle will tell the oscillation frequency.
The proper measurement to diagnose this would be a measurement of S11. From a different amplifier that shares the same problem: <
BTW, I have given up to cure that kind of amplifier. I have made one without feedback around the FET. Everything else either loses a lot of bandwidth to the point of being uninteresting or plays games with parameters that are badly defined. :-(
Gerhard
Am 17.11.20 um 05:05 schrieb Steve Wilson: erhard >> >> No, I was just trying to see if the MiniCircuits engineer understood >> the part. >> >> I work in time, not phase. >
Does it invert?
Make up your mind! Half convinced does not count :-)
Gerhard
A phase shift of 270 degrees at 5GHz could be caused by a propagation delay of 50 picoseconds through the amplifier.
Calculations:
1/5e9 = 0.2ns = 200ps 180 degrees = 100ps 270 degrees = 100ps + 50ps50ps is reasonable for two transistors, (emitter follower plus inverter), at 5GHz.
Probing a circuit to minimize time shift error is difficult at 5GHz.
Matching two probes at 5GHz is difficult.
-- Science teaches us to trust. - sw
Am 17.11.20 um 06:34 schrieb Steve Wilson:
No, not really. My, nowadays somewhat historic 2.5 GHz 1152A probes are the pure joy (apart of running somewhat hot for my fingers). Having the deeper pockets of my customers, something faster should be possible.
But, that all does not answer the question: DOES IT INVERT???
Cheers, Gerhard
The 1152A is only 2.5GHz, or 1.3GHz with the 54845A and 500MHz with the
54810A. The probe is useless at 5GHz.The input capacity is 0.6pf, or 106 ohms at 2.5GHz. This will cause significant error in 50 Ohms:
1/(2*pi*2.5e9*0.6e-12) = 106The propagation delay is 7.5ns. Getting two matched to less than 50ps will be difficult.
Reference:
Don't try to measure a dut when the system bandwidth is about the same as the dut. Use a system with a bandwidth that is much higher.
I would prefer a wideband 10:1 purely resistive probe. Attenuators using distributed resistors are useful up to 30GHz:
-- Science teaches us to trust. - sw
ngs on either S21 or S11. Is this several degrees of phase error something that is important to you? If not then move on.
535945536/ 535945536/That is my point. If you need to have S11 measured so precise you are prob ably playing with a very sensitive circuit. In your case you gave up on it . In the 0.5-2GHz range there are so many fantastic parts available that t ake care of all the finickiness. The OP has not yet stated why he needs su ch a precise measurement. If it is a theoretical thing then so be it.
I have made one
It was not me who brought up "Probes" at all. They have absolutely nothing to do with fringing capacitance on a OPEN reference for a vector network analyzer.
In fact, I'm the one with the VNA and VNA-controlled calibration kit.
Matching probe delays is not difficult, but it does not make sense to match probe delay to 50ps when the scope risetime is 150 ps. And if you insist, you can correct the delays under SETUP -> CHANNEL -> PROBES with 1 ps resolution, forth and back.
Also, the BW of a a 1152A is always 2.5 GHz. It does not get less if you plug it on an inferior scope. It cannot make the scope faster. I do not have an inferior scope, but also the same probe with N/SMA connector for use with other devices. ( 54701A )
The 0.6 pF is essential because the length of the ground strap plays a much lesser role than with the usual 10 pF probes, even at 1:10. It pushes the annoying series resonance up in frequency where it is much less excited from LVC and other fast CMOS risetimes.
The biggest drawback is that it cannot switch to AC coupling, so you constantly have to correct the Y position.
Oh, thanks, but I have the real thing in everyday use on channel
1 and 2 of the scope. 3 is a 500 MHz passive probe and 4 a SMA cable.I have one from TEK, never ever found the hyped 450 Ohm resistor useful for anything. I would not note it if it walked away.
Cheers, Gerhard
Nah, if it were 270 degrees noninverting right at its output, you'd have a 3-pole rolloff.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Here's the TDR/TDT response of a GALI-59, a classic Darlington mmic:
Of one wants maximum pulse amplitude for narrow pulses, you can pull the input up or down to bias the output off-center. It may surprise the RF boys that not all waveforms are symmetric. S-parameters are small-signal linear, which isn't terribly interesting for pulse work. S11 cares a lot about the load too, since the input impedance (and the DC bias!) is mostly set by the feedback resistor from the output.
This is a GVA-63, which is a newfangled self-biasing part:
The s-param charts for these typically cut off on the low-frequency end to hide what's going on. Just apply 5 volts through an inductor and don't ask questions.
Maximum voltage swing is another thing that has to be found by experiment.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
I always put a title block in my sims: title, author, date. It's an engineering document.
-- John Larkin Highland Technology, Inc Science teaches us to doubt. Claude Bernard
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.