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Best topology for low phase noise HF VCO

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Archimedes

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I need to build a low power, low phase noise 40-60 MHz VCO for an IF stage of RF receiever. The VCO is powered from 3.3V and must drive an SPDT switch IC (KISS mixer), so the output has to be fairly symmetrical. Right now I'm using a simple Clapp oscillator followed by a Schmitt trigger, it does the job but I want to make an oscillator with better phase noise performance and at the same time beginner-friendly. I've found a very interesting phase noise reduction method that uses 1/f noise feedback. Looks very promising but I can't find any information about its design. And I'm also not sure if it's applicable at frequencies that low:

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600MHz_1200MHz_Low_PN_VCO.gif

I also saw some cascode and push-push topologies but still no clear design tutorials for those.
 
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Phase Noise is not dependent on oscillator topology only, it depends on many factor such as Quality Factor of the Tank Circuit, Noise of the Transistor etc.
For 40-60 MHz VCOs, Clapp-Gouriet topology is a good choice.Also, Push-Push Oscillators are particularly used to obtain 2nd harmonic of the oscillator, not convenient for your purpose.
Ulrich Rohde is a Guru of oscillators and his **broken link removed** has many valuable papers about how to obtain best Phase Noise from an oscillator.He has also a book and it's highly recommended.You should use a simulator too like ADS or MWOffice too.Analytic approximation that has been very well explained in his book will be your starting point.
 
you need a good device, with low phase noise transistors (most likely a bipolar one), as much RF oscillating power as possible, and a HIGH LOADED Q tuning circuit.

You COULD try a bipolar microwave VCO, say from 4 to 6 GHz, and send it thru a digital divider of 100....

another way to tune it would be to switch in fixed ceramic capacitors for the gross tuning, and fine tune with a varactor +/- 2 Mhz or so.l
 

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