Why function generators have so limited ramp frequency.
Over and over again years after years I meet peoples wondering why ramp functions freq are so limited. There is reasons. Also some times some may tell that why this and that have higher ramp max freq than this other. Specially if we do not care anything, we can set these limits as high as salespersons want, for ads and brochures. Specially some cheap toys have used this, including also some times square.
Now many have showed triangle how this and that can generate higher freq triangle than triangle function is limited, using example generator Arb wfm. Triangle is very easy. All can do fast triangle. But triangle is just special case in ramp waves, integral of square wave having only odd harmonics.
Generator ramp function also can generate this special case triangle. If ramp function is named as triangle and it can generate only triangle and we promise some quite easy linearity, then can set limit more high. Example in SDG6000X this "Ramp" limit is set for 5MHz. Of course it can set also higher.
I have made previously also with SDG1000X some experimental tests. It have factory limit 500kHz and I have rised it lot. It can do. Quite easy. But what happen when rise this limit. With higher frequency it can not anymore keep linearity. But much higher than 500kHz still this special case of ramp function, triangle, can do much higher than 500kHz without problems. And same is naturally with SDG6000X. Triangle is not problem.
As said, triangle is special case. Generator can produce all kind sawtooth ramp waves and this wave is much more difficult and this is main reason why this function max freq. is limited so low. It depends lot of how good linearity we want. Many times these ramps are used for purposes where linearity need be good. Also afaik mostly with these needs we do not need so high frequencies. For what you use ramp? What is real need for its speed? If not need good linearity, for what you need at all this function in practice. I mean serious needs and not playing.
If now test things using triangle, it is nearly like nonsense if we talk about function generator ramp fuunction what can produce all starting from most challenging fast edge sawtooth and up to most easy triangle.
Example if SDG6000X run with 5MHz ramp and set 0.5% symmetry it mean 1ns total time for rise from bottom to top and then start linear ramp down using 199ns. (no it can not do it clean, not even 1% symmetry) many times we accept square wave bottom and top 10% is nearly what ever rounded, ringing etc. But when we look sawtooth... suddenly we do not accept and we want it is nice and clean like in student books.
With 50% symmetry it is triangle, integral of pure square including only odd harmonics. It have quite low level higher freq harmonics and only odd. 1% symmetry high amount of harmonics, and both, even and odd harmonics with SDG6000X over 500MHz. 100th harmonic and still it is far from perfect.
Long to short.
Generators Ramp function limit is mainly not based to just triangle. So if test and demonstrate something related to it, then need remember that triangle is easy and problems start with sawtooth signals and ramp function need cover these all.
If really need faster triangle, for this can use Arb, example in SDG6000X there is factory made triangle what can find in Windows functions and limit is 50MHz but linearity is "as is". Even this is not limit, you can do own faster, double triangle in one Arb wfm and you can get 100MHz "triangle" and so on.
Perhaps this also explain something. Image links to wiki.
https://en.wikipedia.org/wiki/Triangle_wave https://en.wikipedia.org/wiki/Sawtooth_wave
N=number of harmonics
note, triangle have only odd harmonics, saw tooth need even and odd harmonics. So number of harmonics is double (same freq band).
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