Message-ID: <4E355332.6010107@iup.uni-heidelberg.de>
Date: Sun, 31 Jul 2011 15:05:54 +0200
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: frequency doubler and divider
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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