[sdiy] X8 squarewave multiplier.

[Scott Gravenhorst]

A 4046 PLL will do this.  There are caveats, however, a PLL does not respond
instantaneously to input frequency changes, but it can be made very fast (I
have a PLL that does several freq. multiplied outputs, and it is acceptably
fast and tracks over 6 octaves).  There are pole & response time issues that
are made worse by multiplying, but 8 is a pretty small number.  My own
circuit does x12 with outputs at 1F, 1.5F, 2F, 3F, 4F, 6F, and 12F.

At least a square wave is easy for something like a 4046 to track.

To make it multiply the input frequency by integer N, put a divide by N
digital counter in the feedback loop.  Connect the PLL VCO output to the
input of the counter, and the output of the counter then feeds the loop's
filter circuit.  This will force the PLL's VCO to run N times faster in order
to synchronize with the input signal.  Corresponding changes to the VCO range
resistors are necessary, but easy to compute.

Dave Kendall <davekendall at ntlworld.com> wrote:
>Hi all.
>
>Does any one know of a simple circuit that will produce a square or pulse
>wave at 8 times the original input frequency? The idea is to use the
>different waveforms from the EFM LFO5A staircase generator through a VC lag
>to produce new waveforms. The staircase can produce some quite odd
>repetitive waveforms if you tap into different points in the resistor
>network on the 74LS93 outputs, but they are at 1/8th the clock frequency. if
>using it with a Square wave VCO, the clock would need to be multiplied by 8
>to be at the same frequency as the original.
>
>Any ideas anyone?
>
>Dave (just having removed sheep crap from the brake pedal:-)
>

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