# Beginners question

Discussion in 'Electronic Basics' started by [email protected], May 15, 2005.

1. ### Guest

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' ?

El Squid

2. ### Andrew HolmeGuest

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.

4. ### Matt FlyerGuest

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.