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2 GHz Active Probe

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Re: 2 GHz Active Probe

#11

Post by KK7NIL »

amelius wrote: post #2

Is there any open source DIY project to relatively cheaply measure the analog performance of USB 3.1 (10Gbit/s) signals?

Not that I'm aware of.

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.

Re: 2 GHz Active Probe

#12

Post by CamperBob2 »

KK7NIL wrote: post #10
labcomputer wrote: post #7

Earlier quoted context omitted.

> Is there any open source DIY project to relatively cheaply measure the analog performance of USB 3.1 (10Gbit/s) signals? 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 fundam…

The old rule of thumb that you want the bandwidth to be 3 to 5x your baud rate is no longer true. It has been found that BW as low as 0.7x has very little effect in TDECQ and so the newest optical ethernet standards have moved to that for standards testing and the electrical standards will likely soon follow. This BW is also applied as a 4th order Bessel-Thompson instead of an oldschool 1st order gaussian response. R…

There is an interesting new 6 GHz sampling scope that could potentially be useful for some of this work: https://www.eevblog.com/forum/testgear/pocket-sized-6-ghz-1-...

Haven't used it myself, but they seem to have a really solid customer support ethic, given the way the thread developed.

Re: 2 GHz Active Probe

#13

Post by CamperBob2 »

KK7NIL wrote: post #11
amelius wrote: post #2

Is there any open source DIY project to relatively cheaply measure the analog performance of USB 3.1 (10Gbit/s) signals?

Not that I'm aware of. 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 w…

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.

Re: 2 GHz Active Probe

#14

Post by wrs »

CamperBob2 wrote: post #12
KK7NIL wrote: post #10

Earlier quoted context omitted.

The old rule of thumb that you want the bandwidth to be 3 to 5x your baud rate is no longer true. It has been found that BW as low as 0.7x has very little effect in TDECQ and so the newest optical ethernet standards have moved to that for standards testing and the electrical standards will likely soon follow. This BW is also applied as a 4th order Bessel-Thompson instead of an oldschool 1st order gaussian response. R…

There is an interesting new 6 GHz sampling scope that could potentially be useful for some of this work: https://www.eevblog.com/forum/testgear/pocket-sized-6-ghz-1-... Haven't used it myself, but they seem to have a really solid customer support ethic, given the way the thread developed.

And re the original topic, that thread has a reference to a 2.7GHz active probe for $226!

https://www.lasmux.com/product/single-ended-active-probes/

Re: 2 GHz Active Probe

#15

Post by nyanpasu64 »

KK7NIL wrote: post #10
labcomputer wrote: post #7

Earlier quoted context omitted.

> Is there any open source DIY project to relatively cheaply measure the analog performance of USB 3.1 (10Gbit/s) signals? 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 fundam…

The old rule of thumb that you want the bandwidth to be 3 to 5x your baud rate is no longer true. It has been found that BW as low as 0.7x has very little effect in TDECQ and so the newest optical ethernet standards have moved to that for standards testing and the electrical standards will likely soon follow. This BW is also applied as a 4th order Bessel-Thompson instead of an oldschool 1st order gaussian response. R…

Is the analog Nyquist frequency of the signal 0.5x the digital baud (effectively sampling) rate?

Re: 2 GHz Active Probe

#16

Post by 0l »

cushychicken wrote: post #9

In case folks don’t know about the “El Cheapo Special” - you can make very respectable 2GHz passive scope probes with 150ps rise times out of RG-174 coax cable and 1k resistors. 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! Exc…

The catch however is that this can cause (relatively) high resistive loading, so isn't really suitable for all applications.

Re: 2 GHz Active Probe

#17

Post by hatsunearu »

amelius wrote: post #2

Is there any open source DIY project to relatively cheaply measure the analog performance of USB 3.1 (10Gbit/s) signals?

if you want to do this, you generally want a breakout board that breaks out the high speed differential signals to 50 ohm RF connectors and hook that up to a 50 ohm terminated real time scope, and not use a probe.

also for 10gbps per lane, you need at minimum 5ghz bandwidth.

Re: 2 GHz Active Probe

#18

Post by hatsunearu »

amelius wrote: post #4
ComputerGuru wrote: post #3

Earlier quoted context omitted.

What does “analog performance” mean in this context? Are you talking about noise, reflections, etc or something else?

I mean anything that can give more information than just the digital bit errors. Like eye diagrams and such. Basically something that can rate the signal quality on some scale wider than "works? yes/no". Bit error rate is typically too low to give a useful indication.

with the setup you're implying, the eye diagram is all you can get, which to be honest you can extract a lot of information about transmitter-side parameters like the jitter, but you can't evaluate receive performance at all.

receive performance evaluation is done by injecting known amounts of jitter and seeing if the receiver can tolerate that jitter.

Re: 2 GHz Active Probe

#19

Post by jjoonathan »

0l wrote: post #16
cushychicken wrote: post #9

In case folks don’t know about the “El Cheapo Special” - you can make very respectable 2GHz passive scope probes with 150ps rise times out of RG-174 coax cable and 1k resistors. 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! Exc…

The catch however is that this can cause (relatively) high resistive loading, so isn't really suitable for all applications.

It really is suitable for most transmission line applications, though, because transmission line impedance is a fixed target. Top-shelf 20-30GHz probes use this exact technique as their "front end" followed by a 50/100 ohm amplifier to lock in the noise figure:

https://www.tek.com/en/datasheet/trimode%28tm%29-probe-famil...

Re: 2 GHz Active Probe

#20

Post by cushychicken »

0l wrote: post #16
cushychicken wrote: post #9

In case folks don’t know about the “El Cheapo Special” - you can make very respectable 2GHz passive scope probes with 150ps rise times out of RG-174 coax cable and 1k resistors. 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! Exc…

The catch however is that this can cause (relatively) high resistive loading, so isn't really suitable for all applications.

True - but those are the exceptions, not the rule.

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.

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