# Frequency Multiplier

Discussion in 'The Projects Forum' started by Jadams, Jan 14, 2016.

Jan 14, 2016
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Hi guys,

The project I am currently working on is a Theremin and I have decided to incorporate additive synthesis into it. My immediate plan is to be able to select odd harmonics, say the first 4 of them, to be added in order to make the sine wave output into a square wave. I planned to base my circuit on the one contained in the following link:

http://www.techlib.com/files/rfdesign2.pdf

HOWEVER, I have realised that for an input sine wave of varying signal this circuit will not work? My question is am I correct in believing this and is there any way to make it work? Perhaps a heterodyne-esque method of bringing the input signal to a set frequency and then apply the multiplier?

Any help offered is greatly appreciated!

2. ### DickCappels Moderator

Aug 21, 2008
2,650
632
The starting assumption is that "varying signal" is the same as varying in amplitude.

That circuit can work even in the case of the amplitude of the input signal is fluctuating but the fluctuation of the amplitude will be shown in the amplitude of the squared waves on the output. This circuit might be impractical for audio frequencies since its operation relies on the inductor having a large reactance at all frequencies of interest. For audio frequencies you might need inductors of many heneries.

To obtain suitable harmonic content you will probably find that you will have to drive the circuit with a large signal -perhaps 10 volts P-P or more.

You will probably find it much easier to get the kind of clipping you want by using a more "traditional" clipping circuit.

By the way, this circuit by Wenzel is one of my favorites, not only for RF, but in many other applications involving AC.

3. ### sailorjoe Member

Jun 4, 2013
361
63
Jadams, why not just generate a square wave? Is it because you want the amplitude of the higher harmonics to be higher than in a normal square wave? And what is the highest fundamental frequency you want to generate from your Theremin?

4. ### Bordodynov Active Member

May 20, 2015
637
188
Here's a frequency tripler. Choke actually exists (I have a few pieces of miniature reactors). If the inductors do larger size, the transmission ratio increases.
Look

• ###### Frequency_tripler.asc
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Last edited: Jan 15, 2016

Jan 14, 2016
8
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Sorry, by varying signal I meant vary frequency! I should have been more clear in that respect. I cannot generate a square wave because the pitch module mixes two sinusoidal signals and then the difference between them is filtered out - I do not think this works with square waves.
Bordodynov I think that circuit only works for specific frequencies?? Thanks for your help guys.

6. ### DickCappels Moderator

Aug 21, 2008
2,650
632
The Wenzel circuit should work just fine with varying frequencies. The inductor won't care as long as it has enough inductance.