Kwak Clock & Schmitt

[underwurlde]

I see Elso Kwak's much rated 'Kwak Clock 7' design: A Colpitts oscillator using a J309 FET decoupled to an AD8561 fast comparitor.

Q1) Why is this comparitor not arranged to use hysteresis - aka why is it not arranged as a schmitt trigger?

Q2) What happened to the Kwak Clock 8 design.

Q3) Out of interest: Has Elso left these forums?

Many thanks,

Andy

[QSerraTico_Tico]

Originally posted by underwurlde
I see Elso Kwak's much rated 'Kwak Clock 7' design: A Colpitts oscillator using a J309 FET decoupled to an AD8561 fast comparitor.

Q1) Why is this comparitor not arranged to use hysteresis - aka why is it not arranged as a schmitt trigger?

Q2) What happened to the Kwak Clock 8 design.

Q3) Out of interest: Has Elso left these forums?

Many thanks,

Andy

Hi Andy, you can reach Elso at elsokwak225athotmail.com
Replace at by monkeytail (@)
I am sure he will patiently answer all your questions.
Q3: he did not leave; he was banned.

[kevinkr]

Answer to Q1 - Jitter....

[underwurlde]

Thanks chaps.

My thinbking was surely not implementing a schmitt trigger would cause jitter?

I think I am missing something here (hence the question)...

Andy

[peranders]

Originally posted by QSerraTico_Tico
My thinbking was surely not implementing a schmitt trigger would cause jitter?

I think I am missing something here (hence the question)...

You have hysteresis when you have slow rising signals (with noise) and a much faster comparator. Must first thought is to use a schmitt trigger when I'll convert a sinus to square wave.

[peranders]

My second thought is also that many parts in an oscillator aren't not so obvoius.

[Cauhtemoc]

Originally posted by underwurlde
Thanks chaps.

My thinbking was surely not implementing a schmitt trigger would cause jitter?

I think I am missing something here (hence the question)...

Andy

A schmitt trigger has hysteresis, and hysteresis couples energy back to the input. This will screw up the timing if it occurs at the decision point of the comparator.

[QSerraTico_Tico]

Originally posted by peranders
My second thought is also that many parts in an oscillator aren't not so obvoius.

Not so obvious perhaps?
And why then?

[poynton]

Originally posted by underwurlde
I see Elso Kwak's much rated 'Kwak Clock 7' design: A Colpitts oscillator using a J309 FET decoupled to an AD8561 fast comparitor.

Q1) Why is this comparitor not arranged to use hysteresis - aka why is it not arranged as a schmitt trigger?

Q2) What happened to the Kwak Clock 8 design.

Q3) Out of interest: Has Elso left these forums?

Many thanks,

Andy

As you observe, the Quack clock is nothing special in itself.

It is the sum of the parts which makes it better - regulation of the power rails, layout, use of a high-speed comparator instead of a schmitt trigger.

Ray (on the CD63/67 thread - http://www.raylectronics.nl/ ) made a single rail version which works well. I have seen other versions with a high-speed schmitt as well.

Some people swear by the Tent clock and similar - but what's in the can ????

In any case, the external clock is almost certainly fed into the DAC chip via a 'slow' cmos gate !!!

My advice - try it and see !!


Andy


Andy

[Christer]

Originally posted by poynton


Some people swear by the Tent clock and similar - but what's in the can ????

Does it matter? Tent special order them with his requirements for frequency and jitter, and that's what matters. I am not sure he knows himself what is actually inside the cans.