Show us your square wave

[T3sl4co1l]

Just to cross and dot eyes and tees -- these probes are skew matched, right?

Seems plausible it's propagation delay (74AC is a buffered family, and schmitt on top of that), supply (and ground) bounce, and the DIP isn't helping things at all.

Always kind of perplexed that they made 74LVC in DIP, let alone bus drivers and such... but I guess it works well enough on the whole, for logic purposes.  Makes a bit of a mess this way though.

Tim

[BillyO]

Just to cross and dot eyes and tees -- these probes are skew matched, right?

Yes.  The propagation delay displayed is within specification of the chip.

[Dave_g8]

Hi Bill,
Yes, I expect the noise is from the current spikes that will occur during the transitions.

[BillyO]

Just so everyone is aware, the design choices for this pulser were 1) make it cheap and 2) make it relatively easy to build and 3) make it as fast as 1) & 2) would allow so that it can be used to check out the rise time on (slower) scopes.  With a bit of math it does a decent job with scopes up to 200MHz or so.

I know I could have made it perform much better using 74VLC, smaller SMD components and a much smaller footprint, but that would make it much harder for the newbie to build.  Almost anyone who can solder can solder these relatively big SMD resistors.

[TurboTom]

For comparison, here's a similar setup of the square-wave output of my rubidium frequency source, yet utilizing four inverter gates in parallel (no schmitt-trigger) of 74LVC2G04 variety, displayed on a Rigol MSO4000 scope (4GSa/s). The slope rise/fall times have got to be <500ps, considering the contribution of the scope. So my design of an inexpensive a cheap, fairly fast square wave source would consist of a digital crystal oscillator, followed by a single gate driver (maybe a 74VLC1G14), followed by two of the aforementioned dual inverter gates in at least SOT23-6 enclosures with lots of bypassing. I would consider Leo's fast pulser "inexpensive" and considering its performance far superior over any "cheap" solution one could possibly think of. If higher output levels are desired / required, the parallel LVC gate method may be a possible way to go, though.

FYI, this same source connected to an HDO1000 scope (2GSa/s) shows pretty well defined "Gibbs ears" on both sides of the slope, so the fast edges exceed the capabilities of that scope's sampling/display engine. Sorry, no screenshot of this, but neither spectacular either  .

[Performa01]

Here’s the opposite of a cheap solution, but much better suited for lab use – a Siglent SDG7102A Arbitrary Waveform Generator programmed to output a 10 ns wide pulse at 10 MHz repetition rate with 1 ns transition time for both edges.

A quick check with a high bandwidth SDS7404A DSO reveals that the pulse shaper in the SDG isn’t quite accurate anymore at faster edges like this, hence the actual rise time is more like 900 ps:


SDS7404A H12_PR_W10ns_RT1ns_4GHz_Dots

A 500 MHz (actually 570 MHz) SDS2504X HD DSO by contrast, shows a bit of overshoot – this is the price we pay for analog AA-filtering, even when it’s still not very effective:


SDS2504X HD_PR_W10ns_RT1ns_570MHz_Dots

These measurements were taken in Dots display mode, in order to rule out any reconstruction artefacts. But of course, a properly implemented Sinc reconstruction does an equally flawless job:


SDS2504X HD_PR_W10ns_RT1ns_570MHz_Sinc

If you want to see Gibbs Ears, this won’t be achieved with a regular analog filter (as long as it is a minimal phase system). But it’s easily produced with a digital FIR filter, as in the variable bandwidth limiter provided by the SDS7404A. Here’s an example with 600 MHz acquisition bandwidth:


SDS7404A H12_PR_W10ns_RT1ns_600MHz_Dots

[egonotto]

Hello,

Siglent SDG7102A and Siglent SDS7404A is very impressive. Here is a 1 kHz square wave with a 5 MHz but 16 bit PicoScope 4262.

Best regards
egonotto

[Aldo22]

@egonotto

I don't quite understand what you're showing us.
This is more of a trapezoid with 18 microseconds (not nanoseconds) rise time.
What's "impressive" about that?
No offense, I just don't understand it.

[tggzzz]

@egonotto

I don't quite understand what you're showing us.
This is more of a trapezoid with 18 microseconds (not nanoseconds) rise time.
What's "impressive" about that?
No offense, I just don't understand it.

The impressive part is being able to look at the last 1% of the risetime.

With an 8-bit scope the resolution would be inadequate.

[egonotto]

Hello,

I wanted to highlight the capabilities of the Siglent SDG7102A and Siglent SDS7404A combination by showing a rectangle with the PicoScope 4262.
However, the PicoScope 4262 also has strengths. It is a true 16-bit device.

Best regards
egonotto

[Aldo22]

Hello,

I wanted to highlight the capabilities of the Siglent SDG7102A and Siglent SDS7404A combination by showing a rectangle with the PicoScope 4262.
However, the PicoScope 4262 also has strengths. It is a true 16-bit device.

Thanks, but could you explain that for idiots like me?
I assume the signal comes from the AWG (SDG7102A). Does it generate a square wave or a trapezoid?
If trapezoid, why? So that the Picoscope can keep up?
What role does the SDS7404A oscilloscope play here?

What does the whole thing demonstrate? That a trapezoid has no steep edges and therefore almost no overshoot?
I really don't want to annoy you, but I don't get it.
Thank you.

...wer, wie, was,
wieso, weshalb, warum,
wer nicht fragt, bleibt dumm!

[2N3055]

Hello,

I wanted to highlight the capabilities of the Siglent SDG7102A and Siglent SDS7404A combination by showing a rectangle with the PicoScope 4262.
However, the PicoScope 4262 also has strengths. It is a true 16-bit device.

Thanks, but could you explain that for idiots like me?
I assume the signal comes from the AWG (SDG7102A). Does it generate a square wave or a trapezoid?
If trapezoid, why? So that the Picoscope can keep up?
What role does the SDS7404A oscilloscope play here?

What does the whole thing demonstrate? That a trapezoid has no steep edges and therefore almost no overshoot?
I really don't want to annoy you, but I don't get it.
Thank you.

...wer, wie, was,
wieso, weshalb, warum,
wer nicht fragt, bleibt dumm!

It demonstrates that every square wave IS a trapezoid, it is just a question of  how steep are the sides... 

[egonotto]

Hello,

the important sentence I wanted to say was: "Siglent SDG7102A and Siglent SDS7404A is very impressive"

But I wanted to respect the topic of the thread and therefore show a square wave. I spontaneously decided to use the PicoScope 4262 and its generator for this. 

But I think you can also show a square wave of the PicoScope 4262, because it is a special and unique device.

So there is no deeper meaning behind it.

Best regards
egonotto

[Aldo22]

@egonotto
@2N3055

OK, thank you!
Note to self: Don't always look for the deeper meaning... 

Still, I wonder what 16bits are good for, if the signal is completely ironed out by the 70ns rise time of the Picoscope.

[Performa01]

Still, I wonder what 16bits are good for, if the signal is completely ironed out by the 70ns rise time of the Picoscope.

A good DSA (Dynamic Signal Analyzer) also has at least 16 bits and its rise time might exceed 1 µs.

A digital audio recorder also has up to 24 bits, even though its rise time is measured in microseconds rather than nanoseconds.

The Pico cannot resolve fast ringing and HF noise, but it can do very accurate measurements within its rated bandwidth. Apart from the sexy topics like telecommunication and networking, most prozesses in the industry are rather slow and easily covered by 5 MHz.

[egonotto]

Hello,

the square wave has +-900 mV amplitude and 10 Hz. But look at the noise. It is about 0.5 mVpp at 200 mV/div. That is the special feature of the Picoscope 4262.

Best regards
egonotto

[2N3055]

@egonotto
@2N3055

OK, thank you!
Note to self: Don't always look for the deeper meaning... 

Still, I wonder what 16bits are good for, if the signal is completely ironed out by the 70ns rise time of the Picoscope.

If spectrum of your signal is under 5MHz, there is simply no scope that can come even close to Pico 4262..

[egonotto]

Hello,

for contrast a 10 Hz signal with a PicoScope 5444B (1 MOhm input). The rise time is much better here, but the noise is much worse.

Best regards
egonotto

[Aldo22]

@Performa01
@2N3055
@egonotto

Great, thanks for the information! 
It's just a bit off-topic: "show us your highest frequency square wave that looks like a strong square wave" and "kind of curious to see what is the lowest price device is that can produce a really good looking square wave at 1, 5, 10, 20, and 30 MHz?"

I'll show something on-topic.
5MHz from DSO2000 (Scope + AWG)

[Performa01]

Just to complete the SDG7102A topic: here is the fastest slope of 500 ps for both edges. With these settings, the instrument is operated outside its specs and actual rise time is a little slower. Apart from that, we’re starting to see Gibbs Ears in this capture – this is from the ~1.2 GHz reconstruction filter inside the AWG.

I have limited the acquisition bandwidth to 1.25 GHz. This doesn’t make any difference – except for cutting off all the HF noise above 1.25 GHz, because there is no meaningful output from the AWG above 1.2 GHz anyway.


SDS7404A_SDG7102A_Pulse_W10ns_RT500ps_BWL1.25GHz

The genuine resolution is “only” 12 bits, yet we can get a bunch of additional bits by filtering and/or averaging. The example above shows a noise-free ten-times zoom for close inspection of the pre-ringing.

It's just a bit off-topic: "show us your highest frequency square wave that looks like a strong square wave"

Not quite sure what qualifies as “strong square wave”, but if the criterion is that it can be easily identified as such, then I have an example here:


SDS7404A_Demo_Square_500MHz

This is a 500 MHz square wave coming from a SignalHound TG44A tracking generator. Certainly not the cleanest square wave around, yet with nice fast edges.

[Electro Fan]

Not quite sure what qualifies as “strong square wave”, but if the criterion is that it can be easily identified as such, then I have an example here:

About 9.5 years after the original post “can be easily identified as such“ sounds like a reasonable criterion to me
EF