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the VCO sensitivity is the measure of the VCO output frequency variation with the control voltage , and u need to change the control voltage so u can get the chaneel u need
always the VCO is embedded in PLL to get such very low channel spacing
IF there were no noise in your components, then the VCO sensitivity would not matter at all, because if the VCO sensitivity went way up, you would just drop your loop filter gain way down to keep the PLL control loop stable.
However, that is not the case. If there is a lot of op amp or power supply noise in your system, having a VCO with too much sensitivity can be difficult to control, as any little noise perturbation makes the VCO jump a long way in phase/frequency, and there is only so much open loop gain in the control loop to correctfor that jump.
It is a common engineering trade off--you need good sensitivity to tune the full desired frequency range on a limited supply voltage (3.3 v for instance), but can end up with a lot of unwanted phase noise in the full system.
IF there were no noise in your components, then the VCO sensitivity would not matter at all, because if the VCO sensitivity went way up, you would just drop your loop filter gain way down to keep the PLL control loop stable.
However, that is not the case. If there is a lot of op amp or power supply noise in your system, having a VCO with too much sensitivity can be difficult to control, as any little noise perturbation makes the VCO jump a long way in phase/frequency, and there is only so much open loop gain in the control loop to correctfor that jump.
It is a common engineering trade off--you need good sensitivity to tune the full desired frequency range on a limited supply voltage (3.3 v for instance), but can end up with a lot of unwanted phase noise in the full system.
the explain by biff44 is very great! thanks to biff44.
to decide the sensitivity of VCO, you can set up a PLL loop noise model to see the effect of different KVCO.
IF there were no noise in your components, then the VCO sensitivity would not matter at all, because if the VCO sensitivity went way up, you would just drop your loop filter gain way down to keep the PLL control loop stable.
However, that is not the case. If there is a lot of op amp or power supply noise in your system, having a VCO with too much sensitivity can be difficult to control, as any little noise perturbation makes the VCO jump a long way in phase/frequency, and there is only so much open loop gain in the control loop to correctfor that jump.
It is a common engineering trade off--you need good sensitivity to tune the full desired frequency range on a limited supply voltage (3.3 v for instance), but can end up with a lot of unwanted phase noise in the full system.
the explain by biff44 is very great! thanks to biff44.
to decide the sensitivity of VCO, you can set up a PLL loop noise model to see the effect of different KVCO.
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