Hi Andy,
True.
But if the goal is not to obtain a 2x f signal but an accurate 50%
square wave drive signal at 1 x f, this must be a suitable method. And
furthermore the circuit generates a inverted signal without delay too!
This is exactly what i need for the H bridge driver (using IR2113 FET
drivers) that will be fed from the new IQ-TX converter.
Before i tried a CD4093 to get the inverted signal but there was always
a significant delay, causing high switching losses due to overlapping
ON times. Sure, i could try 74HC... types to reduce delay times to the
usual CD4013 worked fine so far in all my PAs.
73, Stefan/DK7FC
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 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 exactly 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
2011/7/31 Stefan Schäfer <[email protected]>
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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