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DIY Logic Analyzer Probe and Pods for Siglent (and LeCroy) scopes

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mawyatt:
The old analog Tektronix scopes had the best trigger system of any available scope at the time, much better than HP. Like much of the old Tektronix analog scopes, this trigger system was a masterpiece of engineering (like transistor ft doubler preamp for example) and utilized ECL gates as fast analog differential limiting amplifiers in the trigger system because of the ECL transistor speed. I doubt much improvement over this superb analog based trigger system over the years other than use of higher ft transistors for faster triggering.

Does any scope have both digital and analog triggering capability?

Best,

oz2cpu:
the last two posts super interesting, but now we are doing it again.. change topic in a thread :-)
how about we find out how the trigger is really made in the Siglent SDS2000 scope ? and continue in the Siglent scope thread ?
since this scope got FPGA front end to handle the ADC's I would guess it is all done in fpga "hardware"

tautech:

--- Quote from: oz2cpu on March 15, 2021, 04:27:43 pm ---the last two posts super interesting, but now we are doing it again.. change topic in a thread :-)
how about we find out how the trigger is really made in the Siglent SDS2000 scope ? and continue in the Siglent scope thread ?
since this scope got FPGA front end to handle the ADC's I would guess it is all done in fpga "hardware"

--- End quote ---
Trigger discussion is highly relevant to this thread and it's already been disclosed the LA trigger path is different to the analog input digital trigger path where instead the LA path uses comparators.

As has already been pointed out the comparator only needs see its threshold has been met not at what level so combined with the slower LA sampling rate that introduces the timing uncertainties we see as jitter.
It's not like this is a big deal when investigating analog to digital signal conversion when using a LA trigger when we have a deep memory scope as we can record the analog events leading up to the digital trigger.

DL2XY:
There is another point to take into account doing timing analyses:
The trigger level is not absolute, each comparator has a hysteresis of about 650mV (relative to input of 10:1 divider).
Depending on rise and fall times that leads to additional delays.



rf-loop:

--- Quote from: DL2XY on March 15, 2021, 10:05:52 pm ---There is another point to take into account doing timing analyses:
The trigger level is not absolute, each comparator has a hysteresis of about 650mV (relative to input of 10:1 divider).
Depending on rise and fall times that leads to additional delays.

--- End quote ---

Handling hysteresis is different in analog channels and digital channels. In analog channel hysteresis window (wide or narrow hysteresis, depending settings) is always "before" defined trigger level. If user change rising edge trig to falling edge, trig level point is same but hysteresis is moved from downside to upside.
 
But as far as I know example usual PECL comparators have just HW fixed Vhysteresis (usually Vhys is settable example using external resistor). Ordinarily threshold level "0" is center of hysteresis window, so +Vhys/2 is above the threshold level and -Vhys/2 is below the threshold level.
This is very different in analog channel trigger. In rising direction of trig, example edge trig, Vhys is below the threshold and for falling direction of trig Vhys is above the threshold level. In analog side also amount of Vhys is proportional, and even more, we have there two user settable proportional amount of hysteresis. (amount of Vhys is proportional mean that it is some amount from used V/div. I do not remember SDS2000X+ but some scope may have example narrow hys 0.3div and wide hys 0.8div (SDS1000X-E series) explained here but unfortunately by Finnish language what is my native lang. https://siglent.fi/oskilloskooppi-digital-trigger-system-siglent.html )

So, example, rising edge, if we set analog channel trig level to 1.5V and digital channels threshold level to 1.5V  trig position in time axis is different. 
Before edge analog is below [Trig level - Vhys].  And Digital side signal is below [Vthreshold - Vhys/2].
Now when signal  start rise in analog side first it cross over [Triglevel - Vhys] and after then it reach [Trig level], result is "Trig"

If trigger is in Digital side. Signal start rise and first it cross over [Threshold level - Vhys/2]  after then come [threshold level] but nothing happen... after then it cross over [threshold level + Vhys/2] and then result is "Trig". 
Time difference depend this rising time ( pitch angle).

So, yes there is difference and user need understand it if he is working with slow digital side rising times and are looking things in nanoseconds range.  Btw, how much it is if rising slope is slow 10ns.  ;) 

User need just understand this for avoid some traps, as is always important what ever feature is used. "Know your tools..." and so on.



About DIY  LA probe. What is thickness  of gold (and what alloy)  in contacts because this is for frequent plug in - plug out use.
Also, PCB material is important. If it is glass fiber etc.. its edge, even if it have some angle, may cause grinding in connector contacts surface. Perhaps example teflon do not so easy wear and tear this connector. Also contact surface gold or other metal alloys are different for resist wear and tear + corrosion + thermal EMF (what is not important just in this case). But it need resist wear and tear and corrosion/oxidation.  Example PCI-E connectors are not at all designed for continuous and frequent plug in plug out. It can last but need use carefully and cable connector need take care about avoid this PCI-E connector wearing.


Cable. (I do not have any idea about prices, but technically interesting)

There is also available many small dimension coaxial cables manufactured example for medical use. No need be just flat ribbon coaxial.. just example multiple coaxial in soft very flexible (also in low temperatures) silicon etc tube..

Example Coonerwire  http://www.coonerwire.com/mini-coax/  CW2040-3695 F  what is 95ohm coaxial with 0.062 O.D. and 13.5pF capacitance. Or CW2040-3650 F what is 50 ohm, 29.5pF  O.D  1mm aka 0.039"

And whole catalog top quality cables  http://www.coonerwire.com/cooner_catalog_rev9-8.pdf

Some wires are perhaps bit expensive, example pure gold cables

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