[time-nuts] Low noise frequency multiplication

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Feb 28 23:43:33 UTC 2007


Stephan Sandenbergh wrote:
> Hi all,
>
>  
>
> How difficult is it to multiply a frequency standard from 10MHz to 100MHz? 
>
>  
>
> I found the recent discussion about amplifying a 10MHz OCXO output from 5dBm
> to 15dBm very interesting. Thanks Bruce for sending me that common base
> circuit schematics - I had quite a lot of fun simulating it and brushing up
> on my electronics and RF knowledge.  One down side to that circuit is that
> it operates from quite a high voltage (24V) causing quite a lot of
> dissipation in the amplifying transistor. When the operating voltage is
> lowered the harmonic content increases (as expected), but most of it can be
> fixed with an output BP filter as Bruce mentioned.
>
>  
>
> The other day I stumbled across the following article on Wenzel's website:
>
>             http://www.wenzel.com/pdffiles/RFDesign2.pdf
>
>  
>
> It describes a way in which an analogue odd-order frequency multiplier could
> be built cheaply with superior noise characteristics. This circuit that is
> described is really simple and quite ingenious. Unfortunately, I would like
> to multiply by 10 (an even number) so I still need a way to at least
> multiply by 2. Commercial low-noise multipliers are in general much more
> expensive than my OCXO. So now I am curious if there is an easy and reliable
> way to get a 10MHz sine up to 100MHz without degrading the phase noise.
>
>  
>
> Regards,
>
>  
>
> Stephan Sandenbergh
>
>        
>
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>
>   
Stephen

Use a Wenzel style odd order multiplier to multiply by 5 after a 
frequency doubler.
For the frequency doubler either use a diode frequency doubler followed 
by an amplifier or a JFET push-push pair with common source RF feedback 
as a frequency doubler. The JFET frequency doubler will have very low 
phase noise if designed properly. For circuit see:

http://www.febo.com/time-nuts/Bruce_Griffiths/JFET_frequency_doublers

It is also possible to use a pair of bipolar transistors in a pushpush 
doubler with common emitter RF feedback, the phase noise will also be 
very low, however biasing the bipolar transistors is a little more 
difficult than biasing a pair of FETS.

Bruce




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