Show us your square wave

[rx8pilot]

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.

[jadew]

I agree, it's an interesting thread, but keep in mind that your cables probably suck so the only information we could rely on is the rising time. Any ringing you see could be caused by the cable or the cable + dummy load (unless you can test them with a different instrument).

I remember managing to get some extremely clean square waves out of my wave gen - that's not the case anymore because I don't remember which cable/dummy load I've been using

Now about the rising edge, it should simply be a function of the bandwidth of the generator. If it's properly designed, the best rising edge will be equal to the needed rising edge to generate a sine wave at the rated bandwidth. If it's better or worse than that, it's poorly designed.

[pickle9000]

Comparison and Teardown of Siglent SDG5162 and Rigol DG4162 Arbitrary Waveform Generators

http://thesignalpath.com/blogs/2014/12/08/review-comparison-and-teardown-of-siglent-sdg5162-and-rigol-dg4162-arbitary-waveform-generators/

[LabSpokane]

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.

The primer:
http://cp.literature.agilent.com/litweb/pdf/5989-5733EN.pdf

[Pjotr]

What is a good square wave? It's one that fulfils your needs, not a theoretical one drawn with a ruler. On the other side you need a scope with sufficient bandwidth an phase linearity (lack of overshoot) to judge that square wave and the DUT tested with it. And what is affordable then? Depends if your interest is just audio gear or do you plan satellite building or complex high speed data communication stuff?

Here my 2 cts. My  DG4102 hooked to a DS2102, my standard home hobby set-up. It is a 10 MHz square wave of the DG4102. Top trace is with a 50 ohm standard lab cable terminated externally with an external 50 ohm  terminator at the scope. Bottom trace is with a 350 MHz/9 pF HF probe connected to a BNC to probe adapter and terminated with a 50 ohm feed through at the generator side. Not much of a difference to see.

At 10V pp:



At 1V pp:



It fulfils my needs for hobby nicely

[T3sl4co1l]

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.

Not the fundamental, but the risetime: scope should be in the 300ps range, so at 8-9ns, it's *definitely* the generator's fault (or... anything inbetween, but..).  Which suggests a bandwidth around 43MHz, which seems consistent with the lumpy "square" at 25MHz.

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).

That's actually contradictory: you can't have RG-58 that's not "chop suey".  The original spec for the stuff is terrible.

Cable that's compliant with the RG-58 spec can be pretty crappy, or pretty good.

Most of the good stuff is made in the same dimensions, but with better construction and materials, and given proprietary manufacturers' numbers.  Belden 9223 for instance.

If you tested its attenuation at 600MHz and it considerably exceeds RG-59 (and more to the point: is only a few dB at ~50MHz), then it's more than enough for this waveform.

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.

I would guess:
- Risetime limited by antialias filter (blah!)
- Ringing possibly residual from filter or internal circuitry, else possibly Zout or line mismatch
- Slight attenuation of the leading edge of the top, possible line loss, but easily also possible due to generator

Tim

[T3sl4co1l]

Wavetek 193, ~10ns rise, 20MHz range, sine/triangle/square, aux generator, AM/FM/sweep modulation, gating, triggering.

Another vintage: Eico 377



Starts with a sine (Wien bridge RC oscillator) that's clipped to a square.  So the rise/fall time is pretty terrible. 

Tim

[Lukas]

I've done some experiments using an ON Semiconductor NBSG11 and some kind of oscillator: That's what I got (sorry for the crappy image, I've only had my mobile phone with me and this thing only saves to floppy disk...):
Scope is an 20GHz Sampler in some old HP 'Digital Communication Analyzer'.





See this thread: http://www.mikrocontroller.net/topic/295617#3335040 (German) for more infos and pics.

I've done an improved version where I mounted the NBGS11 dead-bug-style and directly connected it to SMA connector, didn't come out much better, but was a royal pain to assemble. I'll have to see were I got pictures of that one...

[ovnr]

Keithley 3390 50MHz ARB @ 25 MHz into a shitty GW Instek GDS-2104 100MHz scope. 50-ohm terminated.

[tautech]

Few variations of that posted before for the record. 
Siglent SDG1010 @ 10 MHz 50 Ohm source & internal DSO termination. RG58C/U.
AS previously posted.


10 MHz same cable, 50 Ohm source, 50 Ohm feed-through TEK termination, 1 M DSO input


10 MHz High Z output, DSO 300 MHz probes,10x 1x, 1 M DSO input

[Alex Eisenhut]

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

That's gotta be the best-looking home made anything from the 80s I've ever seen.

[BloodyCactus]

here is a 1, 5, 10, 15mhz square wave from my DG1032Z to a DS2202A

[alex.forencich]

Not exactly a square wave, but here is an eye diagram of 10G Ethernet 64b/66b idle code as received with an Eoptolink DWDM SFP+ module with limiting amp, recorded on an Agilent DSA91304A.  The module is mounted in a Finisar SFP+ dev board with the receive differential output directly connected to channels 1 and 3 on the scope with SMA cables.  The transmitter is another Eoptolink DWDM SFP+ module in a Myricom 10G NIC, with a 90/10 tap to loop the signal back in to the transmitter to keep the link up (sigh...).  An optical attenuator in-line sets the receive power to -8 dBm.  Period is 200 ps, risetime about half of that.  Scope is running at 40 GSa/sec realtime with 13 GHz analog bandwidth. 

[joeqsmith]

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

That's gotta be the best-looking home made anything from the 80s I've ever seen.

Thanks!   Back then I had to build a lot of my equipment.   Here are a few pictures of it...

Next to my Hitachi analog scope.   


Some of the main board.


Top of the main controller board.

[pickle9000]

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

That's gotta be the best-looking home made anything from the 80s I've ever seen.

Thanks!   Back then I had to build a lot of my equipment.   Here are a few pictures of it...

Next to my Hitachi analog scope.   


Some of the main board.


Top of the main controller board.

Beautiful job.

[Smokey]

You want square waves... I'll give you square waves!!!!


Sorry.  I just wanted to be a part of this killer thread and I don't have any really nice square wave equipment.

Edit to add source:
http://en.wikipedia.org/wiki/Cross_sea
http://en.wikipedia.org/wiki/Cnoidal_wave

[tautech]

You want square waves... I'll give you square waves!!!!


Sorry.  I just wanted to be a part of this killer thread and I don't have any really nice square wave equipment.

Classic. 

[Rupunzell]

The ripples at the top of the step response are likely due to the impedance mis-match between the output of that active device, board to connector launch, non-linear board dielectric effects at these frequencies and more. Improvement means using the required RF_microwave board dielectric, designing a proper board to SMA connector launch with impedance matching network to a normalized 50 ohm load. This is the kind of stuff microwave folks do often. The same rules applies to the picosecond pulse world.

Physically small size alone will not achieve optimum impulse response.


Bernice

I've done some experiments using an ON Semiconductor NBSG11 and some kind of oscillator: That's what I got (sorry for the crappy image, I've only had my mobile phone with me and this thing only saves to floppy disk...):
Scope is an 20GHz Sampler in some old HP 'Digital Communication Analyzer'.





See this thread: http://www.mikrocontroller.net/topic/295617#3335040 (German) for more infos and pics.

I've done an improved version where I mounted the NBGS11 dead-bug-style and directly connected it to SMA connector, didn't come out much better, but was a royal pain to assemble. I'll have to see were I got pictures of that one...

[Rupunzell]

Nice to see a properly instrumented and presented picosecond pulse waveform.
Well and properly done.


Bernice

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

[Rupunzell]

This discussion with images has gone a ways to show how proper instrumentation should be done and all the things that can go so very wrong. A single mis-step in the instrumentation set up and the results will easily mis-lead resulting in a very wrong conclusion of circuit or instrument behavior.

Stuff that can go wrong and it becomes increasingly difficult as the rise times shrink and transmission distances grow.

*Poor coax performance. Common RG58 is pretty poor for any serious RF work. This why semi-rigid coax, Gore, Huber-Suhner and similar coax cables with known specifications should be used for nanosecond-picosecond pulse work. Beyond losses as frequency goes up, coax cables often have dispersion which compounds the problems.

*Impedance match for all component in the system. Deviations cause ripples and reflections in the response.

*Don't trust the scope image alone, know what to expect before setting up the instrumentation and if those results do not appear figure out why.

*No matter how much automation, quality-state of the art instrumentation or what not understand every tiny aspect of the test set up. As frequencies goes up, levels goes down and related are pushed to extremes all it takes is one tiny item wrong and BIG errors happen.

*Keep in mind what one is trying to achieve with the measurement as over kill is not always needed to get the desired result. There is a balance here. One does not need a picosecond pulser with matching instrumentation  to test an audio amplifier.

*Then there are probes.. which are an entire universe of good and bad, some times REALLY BAD.


Bernice
 

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.

[DIPLover]

10, 20 and 40MHz square waves from Altera Stratix FPGA Enhanced PLL to Tektronix 2465. CMOS 2.5V IO standard.

The old boat anchor is still beating specs (a little) 30 years after being built (and 10 years after last pro calibration sadly  )

[T3sl4co1l]

Nice to see something old enough to be in KC.   I bet the lamp holder is actual glass.    Any idea on the age?  50s?    I can just see someone driving their high tech relay logic with this back in the day!   

Ahem, I posted a waveform from an Eico 377 earlier..

To be fair, it's probably a kit from the 50s or 60s, but the tech is certainly up there in age.

Tim

[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.

Nice to see something old enough to be in KC.   I bet the lamp holder is actual glass.    Any idea on the age?  50s?    I can just see someone driving their high tech relay logic with this back in the day!   

This model actually made it into "Journal of Scientific Instruments" page 34 Vol 38 January 1961.
The particular one I got was rescued from a skip when one of the Cambridge University Physics Labs was having a clear out. So it is 60s rather than 50s and has probably been abused by generations of physics students.

EDIT : I attach a photo of the Journal excerpt.

[Wuerstchenhund]

That's actually contradictory: you can't have RG-58 that's not "chop suey".  The original spec for the stuff is terrible.

Indeed, but the cable I have is slighlty better:
http://www.pasternack.com/images/ProductPDF/RG58C-U.pdf

All I wanted to say is that the cable is not one of the the $2 items from ebay.

[Yago]

This discussion with images has gone a ways to show how proper instrumentation should be done and all the things that can go so very wrong. A single mis-step in the instrumentation set up and the results will easily mis-lead resulting in a very wrong conclusion of circuit or instrument behavior.

Stuff that can go wrong and it becomes increasingly difficult as the rise times shrink and transmission distances grow.

*Poor coax performance. Common RG58 is pretty poor for any serious RF work. This why semi-rigid coax, Gore, Huber-Suhner and similar coax cables with known specifications should be used for nanosecond-picosecond pulse work. Beyond losses as frequency goes up, coax cables often have dispersion which compounds the problems.

*Impedance match for all component in the system. Deviations cause ripples and reflections in the response.

*Don't trust the scope image alone, know what to expect before setting up the instrumentation and if those results do not appear figure out why.

*No matter how much automation, quality-state of the art instrumentation or what not understand every tiny aspect of the test set up. As frequencies goes up, levels goes down and related are pushed to extremes all it takes is one tiny item wrong and BIG errors happen.

*Keep in mind what one is trying to achieve with the measurement as over kill is not always needed to get the desired result. There is a balance here. One does not need a picosecond pulser with matching instrumentation  to test an audio amplifier.

*Then there are probes.. which are an entire universe of good and bad, some times REALLY BAD.


Bernice
 

Good post, thanks.
To see great square waves is one thing, explanations like yours fill in the whole picture.
Without that, all that is learned is "so and so, has the best square wave, and kit".
Well from my meagre perspective that is!

Oh and welcome to EEVBlog

My rise time is going to be about 6 weeks until I get delivery of 1054z!