emad
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Cairo, Egypt
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Much of the frequency variation comes for the varactor side. Junction caps can modulate the frequency as well but with a much smaller gain. Therefore, varactor biasing needs to be designer very carefully and might very well require large on-chip capacitance.
As for the voltage-biased versus current-biased, the answer is yes, current biased VCOs are better wrt to pushing and this is predominantly because the exhibit less AM noise with supply variation. This, of course, if you bias the current source from a clean reference.
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