Hi - I am trying to get a handle on some switching speed concepts - I beleive it is correct that the faster a signal switches the closer to a square wave it becomes and therefore the more harmonics it contains ?? So just how fast must it switch to contain 'all harmonics' ?
Thanks in advance, El Squid
------------------- Good headwork. You're right! Why, infinitely, of course.
-Steve
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The short answer is: instantly.
The long answer is: all signals are bandwidth-limited. No signal contains an infinite number of harmonics, and no signal has zero rise-time.
Also, it isn't just the number of harmonics which determine waveform shape, but also their relative amplitudes.
You are correct. One of the implications of this is that faster the signal transitions (i.e. shorter rise or fall time) the higher the significant energy content of the higher harmonics that your circuit must handle. As a rule of thumb, beyond a certain point, which alot of times can be aproximated as .5/Trise, you no longer need to worry about the harmonics. A second implication of this conecpt is that it is not posisble to generate an ideal square wave with physically realizable components.
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