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icsoul said:In behavior level or transistor level.
Thanks!~
rfsystem said:Because the loop bandwidth is an AC definition and the basic PLL operation time-discrete, value continuous with special feature that the PFD convert phase difference into values.
So you have to separate analyze the loop:
1. Determine the KVCO, simulate VCO at two different VCO voltages
2. Determine the KCHP, is simply the pulse current level
3. Simulate the transfer function
ChargePumpCurrent -> VCOVoltage
Plot the transfer function of 3. and add the (KVCO/s)*KCHP/(2*pi*DIV) as a scale factor.
Where the loop gain hit the 0dB is the BW.
LvW said:Hi icsoul,
one alternative to find a value for the loop BW by simulation on transistor level is to use frequency modulation.
Most simulators provide a signal source with FM .
You should increase the frequency deviation caused by the FM process slowly step by step and watch the VCO control signal (which should contain the demodulated signal).
When the frequency deviation reaches the loop bandwidth the demodulated signal begins to change its amplitude.
LvW
LvW said:Quote:But I think your method will not work. Did you get the loop bandwidth with your method ever?
Of course, I got the BW by using this method; otherwise I would´nt it propose.
Quote: According my understanding, the AC analysis is face to special operation point. But I cannot give a correct operation point to ensure the PLL is locked when AC analysis is done.
I did not mention an AC analysis; instead it is a pure simulation vs. time.
LvW said:As I have mentioned it in my reply May 9th:
Increase the frequency deviation step by step......
Of course, you should start at reasonable values.
By the way: which kind of PD do you use ?
LvW said:Hello ICSOUL,
of course, you can try to find the loop BW also using an ac analysis.
However, in this case all blocks of your PLL must be linearized before.
Than, this holds only for the locked condition and for input/output signals which are phases.
Normally, this is not a problem - as far as I know - for all units, except the PD.
If you have a simple multiplier PD it is replaced in the linear model by an simple adder. But I don´t know what the linearized model is for the charge pump.
Do you have a linear charge pump model regarding phase inputs ?
LvW