freq doubler

[Paul Perry]

At 02:58 AM 12/01/01 +0800, Toby Graves wrote:
>Does anybody know how to take a nice, pristine, 50% duty cycle square wave
>and double its freq and still have a nice 50% duty cycle square wave?  

Are you just wanting to do this over the audio range, or wider, or what?
The problem is that you cant tell the freq (or period) of the wave until there 
has been at least one cycle.

Roughest might be to integrate the sq wave, which gives a triangle.
Then run the tri to a peak detector, and use a comparator to square the triangle
(which is at 90 deg wrt to the square) then use logic to combine the orig
square and the new out of phase square, to make a new doubled freq square.

(you need the peak detector or similar strategy because the tri amplitude 
depends on the freq)

If you are doing all this over a restricted range, you cd use a phase locked
loop
like a 4046.

paul perry Melbourne Australia

for a non-micro d*tal strategy you cd use a counter that runs up during a cycle,
and athen divide by two, and count down to get the half way mark thru the
next cycle.
With a high enough freq, you will get pretty close to 50%.