What is the input of VCO in a PLL architecture ?

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criterion456

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As we know, the input of VCO is control voltage, which generates output frequency.








The PLL block diagram is as below:



So, here comes one question:

What is the input of VCO in a PLL architecture? As that red circle

(1). Oscillating frequency?
(2). Control voltage?

If it is oscillating frequency, where is the control voltage at VCO input?
If it is control voltage, where is the oscillating frequency from loop filter output?

Thanks
 

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First you say "As we know, the input of VCO is control voltage" then you ask "what is the input of VCO?". First you give the answer to your question and then you ask the question.

What makes you think there is an "oscillating frequency from loop filter output?". The output of the loop filter is a DC voltage. The "oscillating frequency" is the OUTPUT of the VCO.
 
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This might help, attached.


Regards, Dana.
 

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  • Phaselock Techniques (Gardner-2005).pdf
    9.1 MB · Views: 123

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The VCO there has been mentioned by its transfer function so \[ \frac {K_{VCO}} {s} \]
 

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