Hello Stefan, all,
A "single IC" solution to get a 50% duty cycle might be 4046 (or 40HC46) PLL
without a divider (connect VCO out directly to comparator in).
The VCO has a pretty good 50% duty cycle.
73, Rik ON7YD - OR7T
________________________________________
Van: [email protected] [[email protected]]
namens Stefan Schäfer [[email protected]]
Verzonden: zondag 31 juli 2011 16:35
Aan: [email protected]
Onderwerp: Re: LF: frequency doubler and divider
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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