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Trouble with PLL time domain behavioral model simulation

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hhq414

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noise models in time-domain for pll

Hi,all.
I followed the method of kundert and constructed a pll time domain model to simulate the total phase noise.The model can work correctly,but when I extended it to sigma-delta fractional pll,the output phase noise seems unreasonable.The sigma-delta modulator is a MASH1-1-1 one.I wanted to see the output phase noise only from sigma-delta modulator.When the input fractional part is .0,the output phase noise picture is as follow:
 

hhq414

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noise model in time domain for pll

But when the input fractional part is 0.5,the output phase noise is inconsistent with the above mentioned one. Have anyone ever encountered this problem? Any suggestion?
 

mengcy

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phase domain pll model

Hi,I think you'd better present your model here.
As I know,kundert provided model of two domains:1,time domain,to model the transient process of the PLL.
2,phase domain,to simulate the phase noise and its transfer function in the PLL.
The sigma-delta modulation's phase noise is described by a noisetable function.
So we simulate the sigma-delta output phase noise by cadenceRF or matlab,extracted the parameter like bw,n,fc for the noisetable.then we obtain the phase noise by the phase domain model.

Good luck!
 

hhq414

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mengcy said:
Hi,I think you'd better present your model here.
As I know,kundert provided model of two domains:1,time domain,to model the transient process of the PLL.
2,phase domain,to simulate the phase noise and its transfer function in the PLL.
The sigma-delta modulation's phase noise is described by a noisetable function.
So we simulate the sigma-delta output phase noise by cadenceRF or matlab,extracted the parameter like bw,n,fc for the noisetable.then we obtain the phase noise by the phase domain model.

Good luck!
The model I used was time domain model,and the vco_div model for mash111 sigma-delta fractional-n pll is very likely to the model of the papaer attached.
 

hhq414

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Does anyone have the suitable vco_div model for sigma-delta fractional-n pll?
 

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