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Bode plot up to a few 100 MHz
joeqsmith:
https://eng.libretexts.org/Bookshelves/Electrical_Engineering/Electronics/Microwave_and_RF_Design_V%3A_Amplifiers_and_Oscillators_(Steer)/02%3A_Linear_Amplifiers/2.06%3A_Amplifier_Stability
--- Quote from: alm on October 06, 2023, 04:06:56 pm ---
--- Quote from: Martinn on October 06, 2023, 03:51:40 pm ---No - high Z scope inputs with 500 MHz BW exist, so do probes - so why not?
--- End quote ---
What is the impedance of such scope input or probe at 500 MHz based on the capacitive reactance? Would you really call that high impedance?
--- End quote ---
If I could only find scope probes that didn't load a circuit. :-DD I posted some data for the probes I have in that thread. Also showed the loading effects with one of my 10x probes compared with a resistive probe and where the cross over was. Agree with your point, it's not simple and it's costly. We will wait and see how Lasmux's low cost (<$250USD) probes work.
https://www.eevblog.com/forum/testgear/12-ghz-active-probe-project/msg4988716/#msg4988716
************
Video on stability:
mawyatt:
--- Quote from: Martinn on October 06, 2023, 03:51:40 pm ---
--- Quote from: joeqsmith on October 06, 2023, 12:26:19 pm ---Without all four S parameters, how do you measure the amplifiers stability? It's another shortcoming of the low cost VNAs out of China, 2-port 1-path. My work around was to add a transfer relay.
--- End quote ---
I'm not a RF guy so bear with me. Why would I need anything else than in-out (S21) for verifying if a DC-100 MHz low noise amplifier would be stable? You could either look at the transient response (excessive ringing) or the bode amplitude (peaking) to find out its stability margin.
--- End quote ---
Another "tool" from way back 4~5 decades ago was what we called the "Pinger". This simply was a narrow pulser (CMOS ACT logic) configured into an old Tek scope probe which produced a Dirac Doublet type waveform (+ and - Impulse with 0 average to not upset the DUT DC bias balance). A Pot and High valued R allowed setting the amplitude to a low enough level not to over drive the DUT, and not load the DUT too much.
Since just about any practical multi-ordered "linear" system can be distilled into a simple 2nd order system with reasonable fidelity, the "Pinger" would excite the system and one could monitor the response on a scope. The stability could easily be deduced from the response and related to a 2nd order system with an effective dampening and/or closed loop phase/gain margin.
The "Pinger" proved quite useful and allowed signal injection into various parts of the circuit, especially valuable for "Closed Loop" systems, where opening the loop to inject the test signal can be difficult or dangerous.
Somewhat surprised that something similar has not been offered commercially, or least we are not aware of such??
Best,
joeqsmith:
Looking at the step response for low frequency amplifiers is still common. Ping it as you say with different loads.
https://www.ti.com/lit/an/slva381b/slva381b.pdf?ts=1696608820902&ref_url=https%253A%252F%252Fwww.google.com%252F
Martinn:
--- Quote from: joeqsmith on October 06, 2023, 04:18:22 pm ---If I could only find scope probes that didn't load a circuit. :-DD I posted some data for the probes I have in that thread. Also showed the loading effects with one of my 10x probes compared with a resistive probe and where the cross over was. Agree with your point, it's not simple and it's costly. We will wait and see how Lasmux's low cost (<$250USD) probes work.
--- End quote ---
I'm also a big fan of active FET and Z0 probes.
Yes I see your point. 10 pF will have an impedance of around 50 ohms at 300 MHz. So the "DC" approximation is only valid for either very low input capacitances or low bandwidth.
--- Quote from: tautech on October 04, 2023, 07:33:43 am ---
--- Quote from: Martinn on October 04, 2023, 07:24:01 am ---SVA1015X lists "discontinued" at Batronix. Tons of other options though:
https://www.batronix.com/shop/siglent/all-spectrumanalyzer.html
--- End quote ---
:-// It's a current model:
https://www.batronix.com/shop/spectrum-analyzer/Siglent-SVA1015X-VNA.html
--- Quote ---However usable are VNA functions in these "classical" SA?
--- End quote ---
Same HW as SSA3015X Plus. ;)
SVA1000X models have a # of modes with SA and single active port VNA being core functions that provide for a range of S11 and S21 measurements. Optional but 120hrs of trial use are DTF and EMI modes.
--- End quote ---
Is the SVA1015X as "upgrade-friendly" as the SDG6000X? I think when one would buy a VNA, it should cover obvious applications like bluetooth antenna matching, which would already require the much more expensive 3.2 GHz version.
tautech:
--- Quote from: Martinn on October 08, 2023, 02:34:52 pm ---
--- Quote from: tautech on October 04, 2023, 07:33:43 am ---
--- Quote from: Martinn on October 04, 2023, 07:24:01 am ---SVA1015X lists "discontinued" at Batronix. Tons of other options though:
https://www.batronix.com/shop/siglent/all-spectrumanalyzer.html
--- End quote ---
:-// It's a current model:
https://www.batronix.com/shop/spectrum-analyzer/Siglent-SVA1015X-VNA.html
--- Quote ---However usable are VNA functions in these "classical" SA?
--- End quote ---
Same HW as SSA3015X Plus. ;)
SVA1000X models have a # of modes with SA and single active port VNA being core functions that provide for a range of S11 and S21 measurements. Optional but 120hrs of trial use are DTF and EMI modes.
--- End quote ---
Is the SVA1015X as "upgrade-friendly" as the SDG6000X? I think when one would buy a VNA, it should cover obvious applications like bluetooth antenna matching, which would already require the much more expensive 3.2 GHz version.
--- End quote ---
No.
You need get to the 2.1 GHz (different HW) SSA3021X Plus analyzer before any upgrade tricks can be applied to get to 3.2 GHz VNA capabilities. Further study will disclose paths to follow.
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