Show us your square wave

[TheSteve]

Not too horrible for ECL logic feeding multiple sources.

[R_G_B_]

https://youtu.be/ACUbBUydgUQ

[JPortici]

Finally the thing is repaired and i can play at this game too


unfortunately, the fastest thing i got at hand is the trigger output of a rigol scope, just under 1ns rise/fall time

well there is the 250 MHz ECL clock for the plugins.. and one has to be serviced......

[Leo Bodnar]

Also there are other sampler topologies that rely less on the matching of the components so that may be interesting to pursue.  I am not quite sure why Tek for instance only made a couple of samplers based on the travelling wave gate concept and used bridges for others.  It seems like it would be interesting to try a travelling wave design.

All Tek electrical sampling heads for 11800 and perhaps TDS8000 series scopes are based on what used to be called "travelling wave gate" in 11000 series (like S-4.) 
You can see them six sampling diodes here in the SD-26 sampling hybrid.
Leo

[David Hess]

Also there are other sampler topologies that rely less on the matching of the components so that may be interesting to pursue.  I am not quite sure why Tek for instance only made a couple of samplers based on the travelling wave gate concept and used bridges for others.  It seems like it would be interesting to try a travelling wave design.

All Tek electrical sampling heads for 11800 and perhaps TDS8000 series scopes are based on what used to be called "travelling wave gate" in 11000 series (like S-4.) 
You can see them six sampling diodes here in the SD-26 sampling hybrid.
Leo

I think the traveling wave gate design still depends on matching and at least in my experience with the S-4, seems to suffer from more problems with blow-by.

As for a lower cost / lower bandwidth sampling scope its an interesting idea.  Above a few GHz every component gets expensive if you want to do the job properly (connectors, PCB etc) but below say 5GHz things get a lot cheaper.  Will have a think.  Guess it depends on the market - hobby users often go for 2nd hand boat anchors which can be cheap and to be honest not everyone knows how to drive a sampling scope (splitters for trigger signals etc).

The report I have of a rebuilt Tektronix S-2 sampling head with cheap microwave schottky diodes from Avago was a improvement in bandwidth from roughly 4 to 8 GHz.  Tektronix used an RF substrate in that design but it was barely surface mount.

For signal integrity applications there are no special triggering requirements unless a clock is not available.  But the S-2 has an internal trigger pickoff so even that is not an issue.  Sampling the leading edge is of course a different matter requiring a delay line, pretrigger signal, or random sampling.

I am inclined to think the random sampling is the best way for ease of use however it makes for a very complex timebase and it does not work well with internal triggering.

[Leo Bodnar]

I think the traveling wave gate design still depends on matching and at least in my experience with the S-4, seems to suffer from more problems with blow-by.

To some extent all balanced samplers rely on matching the top and bottom paths - both in component parameters and electrical layout.  Travelling wave gate sampling aperture depends on physical distance between the middle and outside sampling diodes and on, say, SD-26 it is less than 1mm.  I won't be surprised if even diode bonding point position is critical.

I could not find any evidence of blowby compensation in SD-24 and SD-26 heads.  However, according to 11800 documentation some heads do have it.

[nctnico]

ADF5341 ADF4351 + Agilent 54845A:


Edit: changed part number.

[Howardlong]

ADF5341 + Agilent 54845A:

Nice, not sure about the part number ADF5341 though?

[David Hess]

That is very interesting about the rebuilt S-2 head working at 8 GHz with the Avago schottky diodes.  Would I be correct to assume that those were SMD packaged devices (e.g. 0201 / 0402 imperial) as opposed to something more exotic like beam lead or wire bonded die that someone managed to retrofit?

The replacement Avago schottky diodes were SOT-23 sized devices but the original diodes in the S-1 and S-2 samplers were not any smaller.

It seems like reverse leakage current is a bit high for many of the RF Schottky devices so I suppose that putting them in series with some slower but low leakage diode could be worthwhile to avoid the integration signal from degrading so much due to reverse biased diode leakage during the "hold" interval.

The measurement of the stored charge happens pretty quickly and the result is placed into a much slower but lower drift sample and hold so I do not think the leakage is a problem.

Random sampling shouldn't be that hard to get going up to a point, I guess it all depends in part on how many ps resolution you want to achieve in your sample acquisition window timing with the bar being raised for every few GHz you want the thing to perform well at.  4 GHz/250ps per cycle not quite so hard, 10 GHz quite a bit more challenging.

It has been a while since I have looked at it but I think the difference is that random sampling requires a timing measurement while sequential sampling can get away without that so the conditions are more controlled.  In practice, random sampling seems to have about twice the measurement jitter.

Say one thing I have wondered about is whether any "non exotic" (read hard to source, expensive) sampler related components (IC scale) exist?  I've heard of such being made in academic projects and from instrumentation vendors like PSPL and so on.  But just for an integrated T/H / S/H / sampler component it would seem like one might find something from the likes of Analog Devices/Hittite, MACOM, or whatever.  Of course if one is willing to spend enough money (hundreds of dollars ++) one can get ADCs with GHz level sampling capabilities and small sampling apertures that are used for undersampling types of applications, but I would have expected something simpler and less integrated and much less costly to exist.  Does it?  Mixers exist, not clear which if any would be applicable even with somewhat larger input signals.  Haven't noticed S/H T/H with ps scale apertures not integrated into ADCs or exotic instrument modules.

I am not aware of any such thing.  The closest I might have seen are diode bridge phase detectors.

[Leo Bodnar]

Here is Tektronix SD-30 40GHz frontend with 8.8ps risetime from early 1990's to add to the party.

Interesting shape of clipping lines.

Signal-facing part is not even ceramic - but some sort of glass.

Those skilled in the art will notice that critical dimension that defines the travelling wave sampler bandwidth is reduced to the minimum.

Leo

[darrell]

It's not actually 100 Hz, but 1.0000001 GHz sampled at 125 MHz causing the sample point to scan the waveform at 100 Hz. Scope probes are on the output of the 2 diode sampler hybrid in an HP VNA  (26.5 GHz). The source is squared up by an MGF4941 GaAs FET and fed via a 20 dB pad directly to a sampler. The ringing on the bottom which is likely due to the bias inductor and DC block capacitor. Fall time is about 45 ps which is probably due to the FET which has -3 dB gain point of about 9 GHz. Any ideas on a faster rise time source?

[qu1j0t3]

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

^ This link is now dead. LabSpokane, do you know any other sources for the document? (And what is the document?)

Thanks

[Howardlong]

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

^ This link is now dead. LabSpokane, do you know any other sources for the document? (And what is the document?)

Thanks

Keysight rebranded version here http://literature.cdn.keysight.com/litweb/pdf/5989-5733EN.pdf

[Insatman]

+5V out, battery powered reed pulser for use as a TDR, pulse calibration or just for frequency response testing.  <400ps Trise

[Insatman]

Adjustable voltage/polarity version of reed pulser.  This one can output from 2V to ~130V positive or negative.  Risetime is a bit longer.  My attempt at making something like the old TEK109 for use in my home lab.

[T3sl4co1l]

Hmm, it's not a coaxial relay, is it?

Tim

[David Hess]

I have thought about trying to make one of those with a mercury wetted reed relay mounted coaxial inside of a brass tube or as a coplanar waveguide to make it part of the 50 ohm transmission line.  Tektronix did this sort of thing for their fastest tunnel diode pulsers.  The Tektronix 7T11 sampling sweep uses this sort of construction for its wide bandwidth trigger circuits.

But most of the high bandwidth oscilloscopes that I would use it for are analog so the low repetition rate becomes a problem.

[Insatman]

sort of coaxial...it's a COTO 9000 series coaxial shielded relay.  In the low voltage version the relay is soldered as close to the BNC connectors as I could manage.  In the slightly slower high voltage version the relay is connected using a socket for easy replacement.  This increases the inductance a bit. 

When I swapped out the coaxial version for a non-coaxial version the rise-time did not change much as the ground is also carried across by my socket arrangement.  I built the larger version with a socket so I could experiment with different relays.   What I also found out is that over driving the relay coil helps with contact bounce. 

I also found that these particular COTO relays can't handle the 1000kV charge voltage I was hoping to use.  Still, 100V into 50ohms is more than enough for the work I am doing. 

[Insatman]

You can get a few 10's of Hz out of these relays.  I set mine to run at single shot or ~10Hz switch selectable.  I tested it up to 30Hz with no difficulties.  COTO claims up to 1x10^9 operations, but I think switching 50ohm circuits will likely degrade this significantly.   I have yet to wear one out however.

[MrW0lf]

Keysight U1282A 2.4kHz, 50% duty into 600 ohms.





Otherwise nice but hydraulic press channel dude should deal with these parasitic spikes.

[RedDogAlpha]

This is a great insight for someone green! Thanks for the post.

[qu1j0t3]

1 kHz and 1 MHz generated by Arduino Duemilanove (program below); a little interference from 16MHz device clock is clear in the 1MHz trace. Rise/fall ~ 19ns.

Scopes: Tektronix TDS 460A (display in "High Res" mode) and HP 1741A (Conv mode).

Code: [Select]

void setup() {
  // for ~ 1 kHz output on PWM pin 9 (OC1A)
  pinMode(9, OUTPUT);

  TCCR1A = (1 << COM1A0); // toggle OC1A on compare match
  TCCR1C = 0;
  TCCR1B = (1 << CS12) | (1 << WGM12);  // clkIO/256 prescaler; clear on timer compare
  OCR1A = 30; // ~ 1 kHz
  TIMSK1 = 0; //(1 << OCIE1A); // set output compare A match interrupt enable

  // ~ 1 MHz on OC0A (digital pin 6)
  pinMode(6, OUTPUT);

  TCCR0A = (1 << COM0A0) | (1 << WGM01); // toggle OC0A on compare match; clear on timer compare
  OCR0A = 7;
  TCCR0B = (1 << CS00); // no prescaler
}

void loop() {
}


[taydin]

10 MHz clock output from my agilent pattern generator, measured directly at the clock pod with the spring ground lead that wraps around probe tip:

[Physikfan]

Here are square waves 32 MHz, 300 MHz and 2.6 GHz of a HP8133A
measured by a Tektronix TDS820, 6 GHz oscilloscope with 44 ps rise time:

Square wave 32 MHz of the HP8133A, x-axis 5ns/div, y-axis 200mV/div:


Square wave 300 MHz of the HP8133A, x-axis 500ps/div, y-axis 200mV/div:


Square wave 2.6 GHz of the HP8133A, x-axis 100ps/div, y-axis 200mV/div:


The rise time displayed in the last image is about 60 ps

[HighVoltage]

I just came across this old Tektronix video from 1961, explaining really nicely about the square wave.
This might be a real good video for the young players...
The Square Wave 1961