As for the question of anyone wanting a 20MHz Sinc pulse, I wonder who would want or need a 1MHz ECG? 
John
Who need. No one.
Who "need". Kids or kids like grown ups just as for playing fun with scope and generator. Whole hobby may be just playing with test instruments alone like with Nintendo. They are main thing in hobby in some cases. Some cases peoples hobby is electronics and so on and test and measurement instruments are only tools, just like screw driver and pliers etc. When these are needed for real work for salary, mostly they are just tools. Who there need any ready made simplest ECG wfm what is only some how "looks like" joke copied from some basic school book, yes we can say there is artifical or better say artist painted QRST parts but after then it is all what it have. If someone need test some system he need very very different and not monotonic wfms for simulate real ECG for test some circuits for it, who think these jokes are useful in any real works but just for kids playing fun and for salesmans.
One purpose I know. Teaching. Example for teaching how to use and adjust oscilloscope for different things and signals. Example exercise lessons for simple trigger settings with different signals for look just wanted details. This can be one piece of whole set of different signals in basic training.
Sidenote(s) to some random readers who just read bit this and bit that and is confused by sampling speed, jitter, ARB detals disappearing and DDS one clock jitter and ARB frequency:I take example about Siglent SDG1000X (because it is in topic)
ARB waveforms in DDS mode when fixed memory length is in use.
SDG1000X have 150Msa/s and ARB memory length is 16384 14 bit "words" for DAC.
One memory length is one ARB waveform (later awfm).
All know working simplified principle is that it reads ARB memory using this fixed 150Msa/s speed and value goes to DAC input.
Now we can read data sheet.
It tell that maximum ARB frequency is 6MHz! ARB memory lenght is 16k. It mean that it can repeat this one ARB memory waveform 6 million times in second (6M awfm/s).
If we think it can repeat whole ARB memory wfm with all its possible details using 6MHz ARB frequency -- this is just totally impossible. Why.
Because awfm length is 16k and it is sampled using 150Msa/s speed.
If we sample every single awfm memory position and we get out 6M awfm/s it need 6M*16384=98304Msa/s = 98.304Gsa/s
All know it is impossible. But data sheet do not tell it directly. User need understand how these work.
Lets look other way. What is maximal awfm/s what can do so that memory length is 16384 and clock is 150M and every data points in memory can take to DAC. 150/16384=0,0091552734375.
It mean that 9.1552734375k, bit over 9k awfm/s is maximum.
Without loosing details maximum ARB frequency is 9.155 kHz ! Not 6 MHz of course.
Data sheet tell:
Arbitrary Wave characteristics
Frequency min 1uHz and max 6MHz.
But just ago I show that max is tiny bit over 9kHz.
Yes, this IS maximum arbitrary waveform repeating frequency in SDG1000X model when memory length is fixed and sampling clock is fixed. 16k memory, 150M sampling speed)
Do they lie.
No.
How it is done. (now this is extrmely simplified)
What happen now if you set ARB speed for 6MHz aka 6M awfm/s.
With 150MSa/s it can do. "Only" need jump over many many points in memory and take just 25 samples. (150/6=25)
Now if there are lot of details in waveform in ARB memory they are just ignored, just jump over like lazy fox jumps. We loose details. (of course it is bit more complex because memory length is 16384 and divide by.... and so on... so there need some what then can see as one clock jitter in final result)
Wait a minute, somewhere I just read that someone have told to my friend who tell to me that ARB can produce even 30MHz or over sinewave, not so nice looking but still somehow nice wave.
Think other way previously told things...
Still bit rounding corners and simplified.
Just told that using 6MHz ARB max freg can read 25 data points when 150Msa/s clock.
Ok. Lets draw 10 cycle sinewave in ARB memory. Then run it with 6MHz ARB freq. Now it can read again 25 samples, 2.5 sample per one cycle.
Yes there is some filters and result may look some kind of "sine". But if you you run it using 3MHz or draw 5 cycles sine and run it using 6MHz you get 30MHz out... now it looks bit better... and if you change frequency, with some freq it can even look quite nice... as also can do with 10 cycle sine in arb memory.
If we need every position in arb memory is used and forwarded to DAC, SDG1000X can max up to 9.155kHz ARB frequency when memory length is 16k andsampling is 150Msa/s. This is hard fact. Every AWG have this limit as long as it is fixed clock with some memory length DDS
After we accept some memory positions loose (jump over) then it can repeat more awfm/s (higher ARB freq).
Siglent have selected max limit as 6MHz what is ok for very simple low detail ARB waveforms. This selection for limit is not based to some truth how it must be. If Siglent set limit to 1MHz all are screaming that neighbourg have higher ARB freq. Also it can set for 10MHz, even more, it can set even for 30MHz. If it is 30MHz all are crying it can not repeat acceptable nearly any other wfm than nearly sinewave or square. 6MHz is just compromise and nothing more, it is not some kind of technical fact limit. For simple awfm it is ok and for complex awfm with dense details it is far too fast for details.
User is master and just user need know his equipment and how to use it for his application. This is why user need know basic simple fundamentals and some principles how just his instruments works. Except if he is using these only for playing fun for loose free times.
Depending user selected ARB freq it can also vary what memory position is jump over and some other things so that average frequency what user have selected is correct. So mostly we can see 6.666... ns jitter in edges. But it is difficult in practice predict what detail is loosed exactly until you are working only up to trusted 9kHz ARB freq.
About this 6MHz ARB limit.
For roughly same result, if we reduce ARB memory to 8k we can rise it to 12MHz and if we reduce memory to 4k we can set limit to 24MHz and result is same. So if you see noname generator what have same clock speed and example you see there higher ARB freq, think carefully what it mean. Example FY6900 have 250Msa/s, 8k memory and 10MHz ARB max. With its max ARB freq it can read same 25 data points from ARB memory as Siglent and all other data points are jump over, where jump over details and variations is depending freq adjustment and producing one clock, more or less semi random, jitter - in FY6xxx 4ns and in Siglent 1000X 6.7ns.
In Siglent TrueArb (and many others similar mode with different names) mode there is not this one clock jitter due to variable sampling clock and ARB memory length.
Originally SDG1000X series have only fixed length fixed clock DDS mode.
Not anymore.Some time ago Siglent add "True Arb" mode also in SDG1000X series. It was software update, just not remember FW version when it happen.
In "TrueArb" mode things are very different.
Now we do not need jump over and periodically change data point what we move to DAC for keep average frequency.
In this mode there is three (main) things what change. One is of course ARB freq as also in DDS mode. But now also memory reading clock change and more, also memory lenghth can change. When stay in its limits user can be sure no detail is loosed *no jump over data points) and no one clock period jumping depending ARB freq.
But this model TrueArb have limits. 1u - 30Msa/s and 2 - 16384 pts. sampling speed is always limited to speed where do not need jump over memory position so user know that all details are included. In this mode cycle to cycle (awfm to awfm) jitter is specified as 2 pts, 300ps RMS @ 20.1MSa/s when direct DDS mode have specified as 6.7ns peak to peak
There is example earth quake wfm in ARB... who can think 6MHz repeating this one quake period where is lot of details is somehow clever... as also ECG as also lot of other wfms including also sinc. These just do not work with maximum ARB freq 6MHz. Users need know even some basics about things.
It is good question to ask for what purpose users typically use or need ARB and with what speed and other paramaters and I do not mean what is nice to have for some niche rare use or just for "nice to have" because some others have.
Total 196 pre programmed wfm in memory. Just for checkbox feature in sales brochure and nothing else in real life. Of course nice for just playing fun. Also with other tools can play fun, even with hammer and saw. Some play fun with nintendo. Some play fun with scope and other instruments.
And because neighbour company have more perhaps other need also add more. Perhaps some year we can see some company advertise they have 10000 ready made ARB wfm in memory, ready for use. Even 196 is some difficult. You need lot of time to find if some there meet your needs. How you select them. In menu they have some names. Some wfm names do not tell nearly anything and you need just select and look. How often you want do it, finding if there is something what you just now need. Who need these.
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Topic: Siglent SDG1000X Waveform Generators (Read 120086 times)