rickman wrote in :

You say the filter removes "all" of the harmonics... that is obviously
not correct. The filter may reduce them, but it does not and can not
completely remove them. The nearest tones (which are also the largest
amplitude tones) will only be reduced a small amount really. Or maybe
you are planning to use a brick wall filter?


One thing I tried briefly, before getting into computers are doing things
with code still a bit shy of getting into digital filtering just yet, was a
switched capacitor filter, the attenuation there is excellent, and you can
easily filter out the clock signal if it's 100 times the pass frequency.

My question intended to ask *WHY* would anyone design a circuit to
produce a square wave and then spend the time and trouble to filter it?


I had a go at answerign that in my other posts just now.. Basically,
conditioning a rough wave by Schmitt trigger into somethign much easier to
process later, often for PLL input. Controlling hysteresis (using positive
feedback) can be especially useful to elimnate some problems with complex
waves that cross the centre more than twice per cycle.