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Date: Sun, 31 Jul 2011 15:31:19 +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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Ah, regarding the overlap times: I successfully tried a SG3525 SMPS=20
driver to obtain a defined dead-time. So i won't need the inverted=20
signal but a 50% duty cycle anyway. Power losses of the FETs (4x=20
IRFP460) have been excellent low!

73s

Am 31.07.2011 15:16, schrieb Andy Talbot:
> No, that doesn't work to give a true square wave.   If the RC delay is=20
> not exactly 50% you get a repeated double pulse waveform and not a=20
> series of equally spaced 2.F pulses.    On dividing this by 2, you end=20
> up with exactly what you had before.
> Been there  - done that.. :-)
> The only practical way is to double the frequency, filter it to remove=20
> all odd order terms and the half fundamental then square it up and divi=
de.
> Andy
> www.g4jnt.com <http://www.g4jnt.com/>
>
>
> 2011/7/31 Stefan Sch=E4fer <schaefer@iup.uni-heidelberg.de=20
> <mailto:schaefer@iup.uni-heidelberg.de>>
>
>     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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Ah, regarding the overlap times: I successfully tried a SG3525 SMPS
driver to obtain a defined dead-time. So i won't need the inverted
signal but a 50% duty cycle anyway. Power losses of the FETs (4x
IRFP460) have been excellent low!<br>
<br>
73s<br>
<br>
Am 31.07.2011 15:16, schrieb Andy Talbot:
<blockquote
 cite="mid:CAA8k23QgKD0vtr2znFwjdqSLWKZy7g3vbdDfM9zJfc4vqQRFLA@mail.gmail.com"
 type="cite">
  <div>No, that doesn't work to give a true square wave.&nbsp;&nbsp; If the RC
delay is not exactly 50% you get a repeated double pulse waveform and
not a series of equally spaced 2.F pulses.&nbsp;&nbsp;&nbsp; On dividing this by 2,
you end up with exactly what you had before.</div>
  <div>&nbsp;</div>
  <div>Been there&nbsp; - done that.. :-)</div>
  <div>&nbsp;</div>
  <div>The only practical way is to double the frequency, filter it to
remove all odd order terms and the half fundamental then square it up
and divide.</div>
  <div>&nbsp;</div>
  <div>Andy</div>
  <div><a moz-do-not-send="true" href="http://www.g4jnt.com/">www.g4jnt.com</a></div>
  <div><br>
  <br>
&nbsp;</div>
  <div class="gmail_quote">2011/7/31 Stefan Sch&auml;fer <span dir="ltr">&lt;<a
 moz-do-not-send="true" href="mailto:schaefer@iup.uni-heidelberg.de">schaefer@iup.uni-heidelberg.de</a>&gt;</span><br>
  <blockquote
 style="border-left: 1px solid rgb(204, 204, 204); margin: 0px 0px 0px 0.8ex; padding-left: 1ex;"
 class="gmail_quote">LF, VLF,<br>
    <br>
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 :-)<br>
    <br>
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.<br>
    <br>
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.<br>
    <br>
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%!<br>
    <br>
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!<br>
    <br>
Later i found on the German wiki site: <a moz-do-not-send="true"
 href="http://de.wikipedia.org/wiki/XOR-Gatter#Frequenzverdopplung"
 target="_blank">http://de.wikipedia.org/wiki/XOR-Gatter#Frequenzverdopplung</a><br>
    <br>
73, Stefan/DK7FC<br>
    <br>
  </blockquote>
  </div>
  <br>
</blockquote>
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