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Show us your square wave
Howardlong:
--- Quote from: nctnico on July 30, 2017, 07:36:00 pm ---ADF5341 + Agilent 54845A:
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Nice, not sure about the part number ADF5341 though?
David Hess:
--- Quote from: evb149 on July 31, 2017, 04:12:29 am ---That is very interesting about the rebuilt S-2 head working at 8 GHz with the Avago schottky diodes. Would I be correct to assume that those were SMD packaged devices (e.g. 0201 / 0402 imperial) as opposed to something more exotic like beam lead or wire bonded die that someone managed to retrofit?
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The replacement Avago schottky diodes were SOT-23 sized devices but the original diodes in the S-1 and S-2 samplers were not any smaller.
--- Quote ---It seems like reverse leakage current is a bit high for many of the RF Schottky devices so I suppose that putting them in series with some slower but low leakage diode could be worthwhile to avoid the integration signal from degrading so much due to reverse biased diode leakage during the "hold" interval.
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The measurement of the stored charge happens pretty quickly and the result is placed into a much slower but lower drift sample and hold so I do not think the leakage is a problem.
--- Quote ---Random sampling shouldn't be that hard to get going up to a point, I guess it all depends in part on how many ps resolution you want to achieve in your sample acquisition window timing with the bar being raised for every few GHz you want the thing to perform well at. 4 GHz/250ps per cycle not quite so hard, 10 GHz quite a bit more challenging.
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It has been a while since I have looked at it but I think the difference is that random sampling requires a timing measurement while sequential sampling can get away without that so the conditions are more controlled. In practice, random sampling seems to have about twice the measurement jitter.
--- Quote ---Say one thing I have wondered about is whether any "non exotic" (read hard to source, expensive) sampler related components (IC scale) exist? I've heard of such being made in academic projects and from instrumentation vendors like PSPL and so on. But just for an integrated T/H / S/H / sampler component it would seem like one might find something from the likes of Analog Devices/Hittite, MACOM, or whatever. Of course if one is willing to spend enough money (hundreds of dollars ++) one can get ADCs with GHz level sampling capabilities and small sampling apertures that are used for undersampling types of applications, but I would have expected something simpler and less integrated and much less costly to exist. Does it? Mixers exist, not clear which if any would be applicable even with somewhat larger input signals. Haven't noticed S/H T/H with ps scale apertures not integrated into ADCs or exotic instrument modules.
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I am not aware of any such thing. The closest I might have seen are diode bridge phase detectors.
Leo Bodnar:
Here is Tektronix SD-30 40GHz frontend with 8.8ps risetime from early 1990's to add to the party.
Interesting shape of clipping lines.
Signal-facing part is not even ceramic - but some sort of glass.
Those skilled in the art will notice that critical dimension that defines the travelling wave sampler bandwidth is reduced to the minimum.
Leo
darrell:
It's not actually 100 Hz, but 1.0000001 GHz sampled at 125 MHz causing the sample point to scan the waveform at 100 Hz. Scope probes are on the output of the 2 diode sampler hybrid in an HP VNA (26.5 GHz). The source is squared up by an MGF4941 GaAs FET and fed via a 20 dB pad directly to a sampler. The ringing on the bottom which is likely due to the bias inductor and DC block capacitor. Fall time is about 45 ps which is probably due to the FET which has -3 dB gain point of about 9 GHz. Any ideas on a faster rise time source?
qu1j0t3:
--- Quote from: LabSpokane on January 16, 2015, 09:06:23 pm ---
--- Quote from: rx8pilot on January 16, 2015, 08:29:43 pm ---This is a surprisingly interesting thread. A square wave being both hard to generate and measure at high dv/dt and frequency.
On the generator side - what do you have to spend to get a high-quality square wave. There are a million Fluke, HP, Agilent, etc on eBay. I am about to buy a 1Ghz scope and need an AWG and just a plain Function Gen (for general purpose uses like injecting noise into a circuit). Trying to learn how to understand the sources of the errors to make full use of the new scope. I have spent too much time chasing my tail on a design only to learn that my measurement was the problem, not the circuit.
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The primer:
http://cp.literature.agilent.com/litweb/pdf/5989-5733EN.pdf
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^ This link is now dead. LabSpokane, do you know any other sources for the document? (And what is the document?)
Thanks
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