Doubling the signal results in a pulse for every transition of the
original wave:

(view in monospace)
            ________          ________
1: ________|        |________|        |________
            _        _        _        _
2: ________| |______| |______| |______| |______

If you double this, you get two short pulses for every transition of the
original signal.  Put this through a flip flop, and you only achieve
signal number 2.

In order to double, quadruple or multiply a signal and keep a certian duty
cycle you need a PLL, or you need to define your input frequency to be
constant, and use a pulse stretcher to get a 50% duty cycle out of #2.
This has very little use, being a constant.

-Adam


Lawrence Glaister wrote:
>
> the xor trick to double the freq results in a waveform that has pulses at
> each edge
> of the original signal. If you need a square wave out, you could always
> quadruple the
> signal and feed the result into a flipflop to restore a 50% duty cycle.
>
> =======================================================
> Lawrence Glaister VE7IT             email: lg@jfm.bc.ca
> 1462 Madrona Drive                  http://jfm.bc.ca
> Nanoose Bay BC Canada
> V9P 9C9
> =======================================================
> ----- Original Message -----
> From: Dan Michaels <oricom@USWEST.NET>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Friday, November 10, 2000 12:38 PM
> Subject: Re: [PIC]: Generating variable frequency square waves
>
> > Anyone,
> >
> > - related to this issue, I know I can use a couple of
> > daisy-chained XOR gates to produce a frequency-doubler ckt.
> >
> > - does anyone good at logic know off-hand if the doubled
> > output will retain the same duty cycle as the input?
> >
> > regards,
> > - danM
> > =========
> >
> > --
> > http://www.piclist.com hint: The PICList is archived three different
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> >
> >
> >
> >
> >
>
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