Andy, Rik, Bill, ...
Am 31.07.2011 16:20, schrieb Bill de Carle:
You can visualize it more easily by drawing it out on paper [...]
Hmmmmmmmmmmmm, yes, i must agree. A pity ;-)
Will go on thinking. But analog filtering of that digital signal means a
much higher effort.
Anyway interesting stuff.
Tnx to all for the hints!
73, Stefan
and taking an extreme example, e.g. say your input signal is 10% high,
90% low. You'd have to set your RC time constant to a much shorter
period. The XOR output will be 2 short pulses close together, then a
long delay, then another 2 pulses close together.
Bill VE2IQ
At 09:05 AM 7/31/2011, Stefan wrote:
LF, VLF,
I just re-invented the wheel ;-) Just by thinking i found one
possible way how to double and divide a rectangular signal, to
achieve an accurate 50 % duty cycle :-)
One could take a simple XOR gatter like a CD4070 and a RC circuit.
The time constant has to be about the half of the period of the
wanted frequency, e.g. 3.6 us for 137 kHz. The output of the RC
circuit (voltage across C) and the original signal is fed to one
single input of the gatter. Then the output frequency will be 2x f
input.
All this can be found in the internet as well, of course. But if you
don't know about that possibility you don't know what to seach in the
web too. At least i haven't found that method by searching and it
also wasn't discussed here in the recent time. Furthermore i never
saw it on a PA design by amateurs i found in the web.
The output signal of the 4070 is then fed to the well known frequency
divider consisting out of e.g. a CD4013. Then output frequency will
be the same as on the input but the duty cycle will be accurate 50%!
This is one method to (re-) obtain a suitable drive signal for a H
bridge PA or class D PA after passing the driver signal through an
optocoupler or so. I'm sure i will use that method now in several
circuits, like in the new LF PA that still causes some problems,
excactly on that matter!
Later i found on the German wiki site:
http://de.wikipedia.org/wiki/XOR-Gatter#Frequenzverdopplung
73, Stefan/DK7FC
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