Vco

YAN-1 said:

Hello everyone. Can someone please tell me why the voltage-controlled oscillator is always modelled as an integrator when it is used as part of a closed-loop system (like PLL). Why is the relationship between its input (voltage) and its output (frequency) modelled as K/s, where K is its gain and s is the laplace operator?

Thanks a lot.

Nichola V. Abdo

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Analog said:

This is because the roots of K/s fall on the j axis. Recall your S plane from controls class. Any pole on the j axis is a pure oscillator. Poles to the right of the j axis are out of control and will saturate. Poles to the left of the j axis are damped sine waves that will decay exponentially. That is why.

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