Nicholas Gray ( wrote:
: John Albert wrote:
: > 
: > Does anybody have any ideas on how to build a
: > frequency doubler. I would like to take a square
: > wave signal (0 to +5v) and double the input
: > frequency. The input frequency can vary between
: > 1Khz and 500khz giving 2Khz to 1Mhz output.

: The most simple way to do this is to use an exclucive-or (XOR) gate and 
: an inverter or two:

:                       _____
:   INPUT -------------|     |
:           |          |     |
:           | |\       | XOR |----- OUTPUT
:           --| >O-----|     |
:             |/       |_____|

: This circuit produces rather narrow output pulses.  You can make these 
: pulses wider by using two inverters in series where I show one inverter.

This approach will not be practical for the huge frequency range he
wants. Even a relatively narrow glitch at 2KHz will be longer than the
entire period at 1MHz.

The only sensible alternative is to use a simple PLL (like the 74HC4046)
and a divide by 2 flip flop in the feedback loop. All you need is the
74HC4046, a 74HC74, 2 resistors and a cap. The output is a 5% duty cycle
at all frequencies. Beats the heck out of a glitch pulse output.


Date: 11 Jul 1996 22:07:52 GMT

Original Subject: Re: Frequency Doubler

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