Show us your square wave

[LaurentR]

DG1022 at full blast: 5MHz square 
Serious edge rate: 22ns rise time. Spec says <20ns. Almost...

5Vrms, 50Ohms throughout. Captured by a DS1074Z.

[tautech]

DG1022 at full blast: 5MHz square 
Serious edge rate: 22ns rise time. Spec says <20ns. Almost...

5Vrms, 50Ohms throughout. Captured by a DS1074Z.

Is that a bit of jitter we see? 

[Electro Fan]

Hi EEVers,

Thanks for all the square wave examples.

Just to confirm, there were a few motivations/intentions embedded in the original post:

1. Best quality achievable at given frequencies - what is the best looking square wave that can be produced at various frequencies (such as 1, 5, 10, 20, and 30 MHz)?  This is independent of the price of the equipment used.  It's interesting to see what types of generators, test leads, and scopes are out there and what they can produce.  Some generators are perhaps optimized for square waves and perhaps pulses, others might be more multi-function.  Again, just looking to see what equipment can produce a good looking square wave.  (A bit off topic but it appeared that some scopes produce especially nice text and numeric readouts that make the values being measured very clear at a glance - 0xdeadbeef's Hameg HMO2024 looked pretty nice.)

2. Definition of quality - this is related to item 1 but beyond the generators, test leads, and scopes involved is the notion of "what constitutes a good looking square wave?"  No doubt rise time is a key attribute but perhaps there are other attributes to consider (such as how much ringing, etc?).

3. Cost to achieve quality - given that various setups produce various levels of square wave quality, which generators (and test leads) are the most cost-effective for each frequency (1, 5, 10, 20, and 30 MHz)?

(PS, What inspired all this was some recent testing of a couple generators; I was curious to see what "par for the course" is at the various frequencies.)  Thanks and please feel free to keep posting square wave images and any related info along with questions and comments, of course.  EF

[tautech]

Now I've got some time to post what the OP wanted to see. 
From Siglent SDG1010 10 MHz AWG.
3 V p-p & 50 Ohm source.
Captured with Siglent SDS2304 using internal 50 Ohm termination, connection 1 M RG58C/U BNC to BNC.

First image as posted previously, 1 MHz from internal SDS2304 AWG. 4 V p-p.


SDG1010 1 MHz


SDG1010 5 MHz


SDG1010 10 MHz


EDIT
SDG1010 Risetime @ 10 MHz = 6.38 nS mean, Std Dev 156 ps over 13000 counts.
From on-screen measurements SDS2304

[tboy]

Rigol DS2072 hacked to DS2202
Rigol DG1032Z
15MHz into 50ohms

[Paul Moir]

Ok, back to what the OP didn't ask for.  Lets get this back on track. 

HP 3312A at 5MHz, under the spec'd 20ns rise time at 3MHz.  Definitely squarish as advertized. 



But things start to get pretty curvy out at 13MHz:  Had the bandwidth limiter on!  Not so bad at 13MHz:



Scope is a Tek 465 at 10ns/div using a BNC T and terminator. 

[rf-loop]

Rigol DS2072 hacked to DS2202
Rigol DG1032Z
15MHz into 50ohms

Why it was stopped before image?
Turn normal sample mode, turn persistence on (example 1-5sec)
Keep it running and take image.

[jpb]

100GS?

It is on equivalent time sampling on a WaveJet so the time resolution is down to that but the points are obtained from multiple waves. The fact that the waves are still smooth is an indication (I think) that there is very little jitter.

[Wuerstchenhund]

It is on equivalent time sampling on a WaveJet so the time resolution is down to that but the points are obtained from multiple waves. The fact that the waves are still smooth is an indication (I think) that there is very little jitter.

Not really. You simply can't assess jitter in RIS mode. RIS is only sensible for signals that are truly repetitive.

LeCroy has published a good paper on RIS:
http://cdn.teledynelecroy.com/files/whitepapers/wp_ris_102203.pdf

"[...] In order to use RIS, the application must meet the following requirements:
1. The waveform must be repetitive.
2. The trigger event must be identical for every sweep.

Repetition is the key. RIS makes the assumption that every waveform segment that is acquired is the exact same analog waveform. Furthermore, it assumes that this same analog waveform is triggered at that exact same place in the waveform on every acquisition. The only difference assumed is that the sampling phase (where the trigger occurs with relation to samples) is changing.

These restrictions on repetition are serious. It means that the waveform must be repetitive, the trigger must be stable, and no non-repetitive nature of a waveform, like jitter etc. can be measured properly in this mode. Failure to honor these restrictions results in severely distorted waveforms with no usefulness whatsoever and erroneous measurements."

What this means is that what you see on the scope could well be complete garbage unless you're sure your waveform is sufficiently repetitive.

For this exercise I would not use RIS or any other ETS variant. The 2GSa/s sample rate of your WaveJet should be more than good enough for the displayed waveform (or probably any waveform that is within the scope's analog bandwidth).

[joeqsmith]

Ok, back to what the OP didn't ask for.  Lets get this back on track. 

Agree.   

You guys with the old Teks < 30ps       Good job!      

Home made ARB I built for a home project back in the 80s.    It can record and playback.  No DSO at home back then....     6800 based, used some 3055s for the output.  PCB for the output driver but wire wrap for the controls, and it's got a lot of pins.         


Putting out some random data......   

[c4757p]

DG1022 at full blast: 5MHz square 
Serious edge rate: 22ns rise time. Spec says <20ns. Almost...

5Vrms, 50Ohms throughout. Captured by a DS1074Z.

Is that a bit of jitter we see? 

Yes, in the DG1022 output. Its jitter is just embarrassing. Whoever designed it has no clue how to generate a variable-frequency signal.

That looks like what I see from my DG1022 at higher frequencies on any scope.

[jpb]

Here is an historic one from a Levell TG150D that I've just been given and hope to restore (it is very noisy at present).

The maximum it can do is 2.5V and 160kHz (nominal 150kHz but the dial goes a bit higher).

EDIT:
I realise that I had the attenuated set for 20dB so I've added a shot with it off below.

[Wuerstchenhund]

The following screen shots are for a Rigol DG1062z which is probably closer to what the OP was looking for.

The images show the DG1062z in square wave mode at 1/2/3/5/10/20/25MHz at 2.5Vpp and with 50% duty cycle. The output was 50ohms terminated into a known good 30cm RG-58C/U cable.

The scope is a LeCroy WavePro 7300A (3GHz bandwidth, 20GSa/s, 48Mpts), the input is set to 50ohms and full bandwidth mode.

The DG1062z's square wave looks ok until 20MHz but above that it's pretty poor (closer to a sine).

[EV]

Tek R7103, S4 with sampling head extender connected straight to Tek 284 pulse generator.

[Howardlong]

Tek R7103, S4 with sampling head extender connected straight to Tek 284 pulse generator.

Definitely a bit of jitter there 

[rf-loop]

The following screen shots are for a Rigol DG1062z which is probably closer to what the OP was looking for.

The images show the DG1062z in square wave mode at 1/2/3/5/10/20/25MHz at 2.5Vpp and with 50% duty cycle. The output was 50ohms terminated into a known good 30cm RG-58C/U cable.

The scope is a LeCroy WavePro 7300A (3GHz bandwidth, 20GSa/s, 48Mpts), the input is set to 50ohms and full bandwidth mode.

The DG1062z's square wave looks ok until 20MHz but above that it's pretty poor (closer to a sine).

Here Siglent SDG5082 
Some amount different what Rigol DG1062Z
Signal from SDG, around 60cm cable and scope input set for 50ohm.

[rx8pilot]

The following screen shots are for a Rigol DG1062z which is probably closer to what the OP was looking for.

The images show the DG1062z in square wave mode at 1/2/3/5/10/20/25MHz at 2.5Vpp and with 50% duty cycle. The output was 50ohms terminated into a known good 30cm RG-58C/U cable.

The scope is a LeCroy WavePro 7300A (3GHz bandwidth, 20GSa/s, 48Mpts), the input is set to 50ohms and full bandwidth mode.

The DG1062z's square wave looks ok until 20MHz but above that it's pretty poor (closer to a sine).

That seems to be a very telling test. My question is how do you tell the difference between the scope limitations and the SG limitations and the test environment limitations (cables, probes, etc).

I would hope that a 3Ghz, 20GS/s scope is not the limitation here but I am not sure how to know. When I see top and bottom ringing, what are the possible origins of that error?

[nuno]

Tek R7103, S4 with sampling head extender connected straight to Tek 284 pulse generator.

Uooouu, we can even see the electrons, lol

[BloodyCactus]

I can take square wave pics on my 1032Z tonight after work, looks good at low freqs, but at its max which is 15mhz I think, its really a sine wave which is really disappointing.

[katzohki]

Quote from: rx8pilot on Today at 05:43:29 AM

That seems to be a very telling test. My question is how do you tell the difference between the scope limitations and the SG limitations and the test environment limitations (cables, probes, etc).

I would hope that a 3Ghz, 20GS/s scope is not the limitation here but I am not sure how to know. When I see top and bottom ringing, what are the possible origins of that error?

My guess is that the ringing seen on my and many other scope shots is the capacitance in probes, cables, scope input etc and the lack of 50 ohm termination. The rise time / slope of the signals at high frequencies is probably tied to limitation of the function generators.

Maybe someone can post a picture of terminated vs unterminated to illustrate the difference. That or I will after I pick up my 2 new FGs in a week.

[Wuerstchenhund]

That seems to be a very telling test. My question is how do you tell the difference between the scope limitations and the SG limitations and the test environment limitations (cables, probes, etc).

I would hope that a 3Ghz, 20GS/s scope is not the limitation here but I am not sure how to know.

I'm pretty sure the scope isn't a limiting factor here. We're talking about square waves of 25MHz and below and 3GHz (120 times the frequency of the 1st harmonic) is more than enough bandwidth to capture all relevant frequency components. The scope has also been calibrated pretty recently.

The cable has been tested a while ago up to 600MHz. I also did a quick comparison with a brand new 1m RG-58 cable and the results are the same (both cables are high quality cables and not some cheap chop suey stuff). This aside, some time ago I also used the AWG with my other scope (LeCroy WaveRunner 64Xi 600MHz 10GSa/s) and the 25MHz square wave was as shit then as it is today.

So I'm pretty sure that the measurements are valid.

I guess the reason for the bad results at 25MHz is in the slow edges of the DG1062z.

When I see top and bottom ringing, what are the possible origins of that error?

Difficult to say but I'm sure it's from the AWG. Maybe there's a mis-match with the internal termination (I'll see if I can check with external termination tomorrow).

I also noticed that at higher frequencies the DG1062z shows some slight jitter.

[0xdeadbeef]

Honestly I think the bad ringing in the plateau between the edges mainly comes from the signal generators.
The small overshoot and ringing directly at the (rising) edge even hints towards a lack of capacitance.
Besides, I posted HiZ vs. 50Ohm screenshots. There are differences but they are not overwhelming.

[Wuerstchenhund]

Here Siglent SDG5082 
Some amount different what Rigol DG1062Z
Signal from SDG, around 60cm cable and scope input set for 50ohm.

Interesting, it seems the SDG5000 has much shorter edges than the DG1062z (which is a bit disappointing really, considering the Rigol's price tag).

Nice scope. HP 54500 Series I guess?

[nuno]

This is from the DS1104Z-S. Not famous. Coax from sgen output to a T on the scope input and a 50 Ohm terminator (except for the amplitude doesn't actually make any relevant difference, terminated or not).

[rf-loop]

Nice scope. HP 54500 Series I guess?

Yes, 20 years young workhorse, Hewlett-Packard  54522A.