2 GHz Active Probe
jmw.name
jmw.name
Clip the cable in half, solder the core to the 1k resistor, and the other end of the 1k resistor to the signal you want to probe.
Solder the shield braid to board GND.
50ohm terminate your scope, set probe amplification to 20x, and voila!
Excellent tip recommended both by Paul Horowitz (Art of Electronics) and Howard Johnson (High Speed Digital Design). Works like a charm!
https://www.tek.com/en/datasheet/trimode%28tm%29-probe-famil...
Most modern systems aren’t discrete transistor amplifiers where an arbitrary 1k to gnd will massively affect bias point or circuit operation.
For digital interfaces, or power supplies below ~24V, it’s a great high bandwidth probe option. Much cheaper than active probes too.
receive performance evaluation is done by injecting known amounts of jitter and seeing if the receiver can tolerate that jitter.
For this kind of thing (measuring eye diagrams and such, as you mentioned in another comment) you'd need a probe-oscilloscope system with (at minimum) 30 GHz at the probe tip. Realistically you'd want 50 GHz, and more is better. Recall that square waves are composed of odd harmonics of the fundamental (~10 GHz), and the more harmonics you capture the more fidelity you'll have to the original.
I don't think there are any real-time scopes with this much bandwidth, so you will need a (equivalent-time) sampling oscilloscope. Keysight might make one, but it probably costs "call us" dollars.
[Edit: Actually, it looks like the SD-32 sampling head for the Tektronix 11800 series of sampling scopes does claim a bandwidth of 50 GHz. That plugin does not have internal triggering though, so you would need to add a trigger recognizer head and arrange for an external trigger signal. Also, don't buy these used on eBay unless the sell offers returns because the sampling diodes in the frontend are very delicate.]
One additional wrinkle is that super-speed USB uses a differential pair with a characteristic impedance of 50 Ohms (each side of the pair is 100 Ohms, and terminated with a 100 Ohm resistor). That means you'll need a differential probe (or two probes and an oscilloscope that can do math).
I don't know of any DIY project with those ambitions, but the most likely route for something DIY is a passive Z0 probe: You want the DUT-probe interface to look like an impedance-matched power divider. That calls for a probe impedance of 10x (or even 100x) the transmission line, so 500 or 5000 Ohms.
Anyway, I don't know of any DIY project that fits your needs, but the terms to search for include "Z0" and "passive".
Practically, this probably ends up fairly similar to what I mentioned above, since "making the other end talk USB3" means receiving with the bits it sends and responding in a way it expects.
But, yes, in-situ / solder-down probes can definitely simplify things because it gives you the flexibility to do things like remove the existing termination (assuming the termination isn't in the receiver IC itself) and use the 1x Z0 soldered-in probe as the terminator.
I just probably wouldn't do this part:
> then have a front-end IC that is hopefully available and that is fast enough to do the sampling
This gets complicated fairly quickly. It sounds like you want both real-time sampling (so you can do something with the bits and "make the other end talk USB3") fairly high resolution (so can see something in the eye diagrams). That calls for a digitizer with like >=5 bits and a sample rate of >100 Gsps... Which basically doesn't exist, AFAIK. Oscilloscopes which sample that fast are interleaving multiple digitizers, and this isn't really something you can DIY.
However, if you just want eye diagrams, you can use ET sample techniques (running at a pedestrian ~10-100 ksps), together with something to synchronize the sample to the USB clock, to fill in the entire horizontal width of the eye diagram. There are several catches: First is that it takes a very large number of triggering events to fill in the diagram. Second, the 100 ksps sampler needs a very short capture window (on the order of picoseconds). Third is that you "miss" most bits in the data stream, so you don't capture any real USB data while making the eye diagram.
Fortunately, you can buy a used sampling oscilloscope which does this for you. It captures the samples, relates them to the USB clock, and places them in the correct place on the x-axis. You just need to construct probes to bring the signal into the scope. The 11800 I mentioned is one such example, but there are others, too.
Real-time scopes go up to 110 GHz now! Sampling scopes are unfortunately dying out now a days.
Haven't used it myself, but they seem to have a really solid customer support ethic, given the way the thread developed.
Ex:9600 baud FSK signal centered at 440MHz still needs something capable of capturing around 440MHz, but this has nothing to do with baud rate. A 500MHz scope would do well for acquiring the signal.
Practically radios often divide the problem into two parts, first use a mixer to shift the signal down and filter out the parts you don't want, then decode the FSK which remains at a much lower frequency.
This is the governing limit: https://en.m.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theo... and it considers things like SNR as well.
For a real receiver circuit you'd want to sample at least once a symbol obviously (so RX sample rate equals the baud rate). In practice you'd want more than that so you can better do DSP afterwards to remove channel losses and such. For a test instrument, it's going to depend on what exactly you want to see. Most standards define a required filter shape and BW for testing and you need enough sample rate in your scope to be able to implement this (usually in DSP).
Sampling systems are about $20k - 50k without probes in this bandwidth.
Keysight DCA-M and picoscope have the best public prices, and exfo has an eye analyzer in that price range. There’s also DCA-X but nobody wants to pay 10k extra for a touchscreen.
Unfortunately tek doesn’t make electrical sampling systems anymore, just optical.
All the other scopes on the market use time interleaving (time multiplexing) which has much better characteristics but requires that the ASICs have much higher Ft, which requires a significant capital investment.
Sampling scopes are not actually that much cheaper now a days, especially after you take into account the cost of the clock recovery device that you would need to build a proper eye with a sampling scope (I discussed this further in other parts of this thread).
You could generate an eye diagram with an old sampling scope or BERT for probably less than $2k, but those likely wouldn't have the proper clock recovery, which means your horizontal would be sort of pointless. You'd have to make a separate clock recovery module to sit between your USB 3.1 DUT and the instrument.
The other option would be to try and make a real-time ADC with enough BW (at Tek we demoed USB 3.1 debugging with just 10 GHz on an MSO6B, even though compliance testing requires 12 or 15 iirc) and memory depth to do the clock recovery in DSP. This would be a very significant challenge, but might be possible, depending what ADC's are on the market now a days.
It strikes me that if you ran it long enough, there is probably no reason why a sampling scope couldn't do the same thing. It would need even more DSP eggheadery than the realtime scope, of course.
If you just trigger off the edges in the signal all you'll be measuring is the scope jitter.
also for 10gbps per lane, you need at minimum 5ghz bandwidth.