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# How to design a frequency doubler without using PLL?

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#### alam.tauqueer

##### Full Member level 2
Hi ,

I want to know how can we design a frequency doubler without using PLL?

It would be great help.

Regards
Tauqueer

frequency doubler integrator

I built one of these lately,

If you have a square wave LPF to make sinusoidal (or close too it)

Full wave rectifier

and a comparator, make put a pot on the referance voltage so as you can tweak it to get a 50% duty cycle. It works a treat!

Re: Frequency doubler

I didnt get you clearly.Could you please explain again.

Regards
Tauqueer

Re: Frequency doubler

Ok,

If you pass a square wave (clk) through a LPF with a cut off at the close to the clk frequency you'll get out a sine wave. If your original signal is a sinewave don't bother with this part.

Now full-wave rectify the sine wave

then on the rectified signal, place a comparator (comparing vith a voltage somewhere between 0V and Vpeak, (easiest to use a pot connected as a voltage divider), thweaking this voltage will alter the duty cycle of the square wave output.

If you need to sharpen the edges after the comparator, place a couple of inverters on the end.

If you want to get a sine wave back - LPF

Depending on your rectifier choice, you may have to use a fully differential amp (or some other way), to convert your single enden sine wave into a differential one.

Re: Frequency doubler

alam.tauqueer said:
Hi ,

I want to know how can we design a frequency doubler without using PLL?

It would be great help.

Regards
Tauqueer

Re: Frequency doubler

What is an analogue integrator? (I know what an integrator is, but I assume this is something different.)

And how do you double a frequency with it?

cheers

Frequency doubler

Is this solution feasable ?
Can you post some matirial on this circuits.
Thanks

Re: Frequency doubler

master_picengineer said:
Is this solution feasable ?
Can you post some matirial on this circuits.
Thanks

which solution?

The one I gave works, you have to set the duty cycle by eye(using a scope).

I can send you a block diagram if you want. It's pretty straight forward.

convert clock to sinewave (if necessary) with a LPF
Make clock differential (if you use a bridge rectifier) with transformer of fully diff amp or if you use a precision rectifier no need to make differential.
On the rectified sine wave use a comparator to create a square wave clock, tweaking the reference voltage to set the duty cycle.
If you want to get a sine wave back - LPF again. (you could probably LPF the rectified waveform and retrieve a sinewave from there, I'm not sure though.

Frequency doubler

If you have no limitations on the output duty cycle, then you can do the following :
apply the input signal (with period T ) to delay line (or a buffer) whose delay is adjusted to (T/4) , then XOR the input signal with the delayed one ..
but take care , this circuit doesn't work all the time.

harkark

Points: 2