CP has an output voltage of 1.2V~Vp3-0.3V, but after adding an CMR voltage 3V, voltage range becomes 1.8V~Vp3-0.8V. How does this work? I feel confused and when designing circuits that extending VCO tuning voltage. Thank you!
The VCO tuning range is limited to less than the output voltage range because the loop needs to leave room for the tuning voltage to overshoot. For example, if you are locking to a VCO tuning voltage of (Vp3 - 0.8 V) from a lower voltage, when the loop is locking, the voltage will first shoot up higher than (Vp3 - 0.8 V) before it returns to (Vp3 - 0.8 V).
If the voltage overshot above (Vp3 - 0.3 V), then the loop would go into saturation and the transient response can become unpredictable.
The CMR voltage does not relate to this.
Thanks for your reply. I had mistaken the voltage range 1.2V~(Vp3 - 0.3 V) as the result of (CP+)-(CP-). I think range of (CP+)-(CP-) is -2V~2V, then if it adds with 3.3 V CMR, result will be 1.3V~5.3V. Under fastlock and normal operation, results will be different.
However, I wonder that (CP+)-(CP-) can only range from -2V~2V(example given in datasheet), or it can vary wider, for example, -4V~4V. Thank you!
I sent you an email with a document that should be helpful.
Let me know if you need further help.
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