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what is the defination of the transfer function in PLL

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lfq521914

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hello,
I am confused about the defination of the transfer funtion for a loop filter in PLL.
In the book "PLL Performance, Simulation, and Design" which was written by Dean,it is said that "the loop transfer function will be defined as the change in voltage at the tuning port of the VCO devided by the current at the charge pump.
In the cause of a second order loop filter,it is simply the impedance."But for a third order loop filter ,it is not the case according the defination mentioned above.
My question is ,how can I get the equation of the transfer function for a third order loop filter?Your help will be great appreciated.Thanks![/quote]
 

radiohead

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Just calculate the transfer function from CP current source to the (high-impedant) VCO tuning port using Kirchoff. That's all.
 

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