vco pushing

Hello Everyone;
I want to know wether VCO load pulling and pushing affect the performance of a PLL or not. Please help me. Can anyone refer me to an article or a book about this problem?

A PLL is a control loop. It senses the phase of the VCO, and compares it to some reference. If there is a phase error, it "tunes" the VCO either up or down to minimize the phase error. A number of factors influence how quickly it corrects a phase error, if there is an overshoot or ringing if there is a sudden phase error that needs correcting, etc.

If you have a system that is very sensitive to phase errors, and you allow the load to the VCO to suddenly change (like switching the VCO path from one load to another in a SP2T switch), then there will be a transient phase error to deal with.

You can minimize the effect somewhat by using buffer amplifiers, attenuator pads, ferrite isolators, etc. But you might need a lot of isolation in certain systems. In any PLL that uses a digital divider, there will be a time delay before the PLL even starts to correct a transient phase error.

Rich