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References: <4E355332.6010107@iup.uni-heidelberg.de>
Date: Sun, 31 Jul 2011 14:16:15 +0100
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From: Andy Talbot <andy.g4jnt@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: LF: frequency doubler and divider
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No, that doesn't work to give a true square wave.   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.    On dividing this by 2, you end up with exactl=
y
what you had before.

Been there  - done that.. :-)

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.

Andy
www.g4jnt.com



2011/7/31 Stefan Sch=E4fer <schaefer@iup.uni-heidelberg.de>

> LF, VLF,
>
> I just re-invented the wheel ;-) Just by thinking i found one possible wa=
y
> 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 ti=
me
> 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 discuss=
ed
> 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 th=
e
> 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 o=
r
> 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<http://de.wikipedia.org/wiki/XOR-Gatter#Fr=
equenzverdopplung>
>
> 73, Stefan/DK7FC
>
>

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<div>No, that doesn&#39;t work to give a true square wave.=A0=A0 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.=A0=A0=A0 On dividing this by 2, you e=
nd up with exactly what you had before.</div>

<div>=A0</div>
<div>Been there=A0 - done that.. :-)</div>
<div>=A0</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>=A0</div>
<div>Andy</div>
<div><a href=3D"http://www.g4jnt.com/">www.g4jnt.com</a></div>
<div><br><br>=A0</div>
<div class=3D"gmail_quote">2011/7/31 Stefan Sch=E4fer <span dir=3D"ltr">&lt=
;<a href=3D"mailto:schaefer@iup.uni-heidelberg.de">schaefer@iup.uni-heidelb=
erg.de</a>&gt;</span><br>
<blockquote style=3D"BORDER-LEFT: #ccc 1px solid; MARGIN: 0px 0px 0px 0.8ex=
; PADDING-LEFT: 1ex" class=3D"gmail_quote">LF, VLF,<br><br>I just re-invent=
ed the wheel ;-) Just by thinking i found one possible way how to double an=
d divide a rectangular signal, to achieve an accurate 50 % duty cycle :-)<b=
r>
<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 frequenc=
y, 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 do=
n&#39;t know about that possibility you don&#39;t know what to seach in the=
 web too. At least i haven&#39;t found that method by searching and it also=
 wasn&#39;t discussed here in the recent time. Furthermore i never saw it o=
n 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 d=
ivider consisting out of e.g. a CD4013. Then output frequency will be the s=
ame 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 cl=
ass D PA after passing the driver signal through an optocoupler or so. I=
9;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 href=3D"http://de.wikipedia.o=
rg/wiki/XOR-Gatter#Frequenzverdopplung" target=3D"_blank">http://de.wikiped=
ia.org/wiki/<u></u>XOR-Gatter#Frequenzverdopplung</a><br><br>73, Stefan/DK7=
FC<br>
<br></blockquote></div><br>

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