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How to design a VCO that has a good performance

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redhat

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i want to design a vco that works with center frequency 950MHz with no phase noise performance requirements (i don't want to buy it), so what is the value of Q that i should take to have a good (acceptable) performance? the resonator is a 4 element lumped resonator what should be the input/output load resistance?the output is a negative resistance amplifier and the input is a voltage source.when putting the varactor ,should i put it instead of one of the shunt capacitors or in series with it?i am going to use BB149 varactor and i can't calculate its Q because i don't find parallel resistance value Rp in the datasheet.

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xtasa

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Re: Some VCO Questions

Hello Redhat,

The easy way to design VCO is to use your resonant circuits and amplifier at the loop with no real negative impedance amplifier . With elements you can adjust resonant frequency that is shift 0 or 180 degree or what is necessary it depends of amplifier type in feedback loop.The simple solution is to use some MMIC amplifier like ERA ... MAR ....MSA You can use varactor diodes instead shunt capacitors . This is a wide band type of VCO and Q of varactor have small influence specially if you put in series C with diodes. Similar solution you can find in article from M. Vidmar published in VHF Communications few years ago. I also designed more than 10 years ago VCO who worked 1.5 octave bandwidth in range 22 Mhz -1.2 Ghz with resonant circuts like yours and with small change some components and of course the main change is L which which determine resonant frequency and bandwidth of change.

GL XTASA
 

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