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Date: Sun, 31 Jul 2011 16:35:25 +0200
From: =?ISO-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@iup.uni-heidelberg.de>
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Subject: Re: LF: frequency doubler and divider
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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
>>
>