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why a vco is nonlinear ?

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dinosaur078

dinosaur078

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dear everybody
i am studying, practicing design of VCO , and i know the parameter KVCO is very important. i also know that , every the transfer curve of KVCO should be a line .
if it is not a line , that vco is nonlinear .
so i wonder that , in theoretical. what reasons can make vco become nonlinear ? and how can fix this problems ?

many thanks in advance
 

It depends on the varactor curve, and the LC formula - freq will vary proportional to sqrt(1/C), so it's
non-linear.
 

in theoretical. what reasons can make vco become nonlinear ? and how can fix this problems ?
Click to expand...
All the process variations, supply and temperature variations add to the system non-linearity. List is still broad with second order effects.
For example, VCO stage gain vary with process, supply and temperature, and this gives the non linear effect to the output frequency.

- - - Updated - - -

You can make stage gain independent of process ,supply and temperature variations. You can use band-gap voltages for reference and PTAT current to cancel temperature effect.Still you need to use trimming and much more other methods to cancel this.
 

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