Measuring Dead Zone of PLL

[barbara111]

Hello,
Could you help me to measure dead zone of PLL with Matlab Simulink?

Thanks.

 

[leo_o2]

dead zone is measured when there is time error between PFD and PLL fails regulation.

 

[skal81]

If you plot the PFD-CP current versus reference-feedback phase difference, the "dead zone" refers to region where the current does not change regarding the phase difference (a flat part in the graph).
This dead zone is due to some circuit non-idealities (switching time and other), which means unless you did model those it will not happen in Matlab.
Simple PLL models (to check stability and loop response) does not take those into account.
You will be able to measure the dead zone from Spice simulation.

 

[barbara111]

Could you help me to find some blocks, that I can measure Dead Zone.

In Matlab Simulink I have a block wich includes both phase detector and charge pump, and I also entered the charge pump current's value in its properties. My problem is that I want to get the values of current versus phase difference for measuring dead zone.

 

[FvM]

As skal81 explained, it's unlikely that you'll see dead zone behaviour in your Matlab simulation, unless respective empirical measured device properties have been added to the model.

 

[barbara111]

Can I replace my block PhD-ChP with other blocks, that could give me opportunity for measuring dead-zone?

 

[leo_o2]

One way to measure it is to break the loop at the feedback input of PFD.

 

[biff44]

I am not too familiar with simulink, but it has capability to model gates. Just hook up some XOR gates and small time delays so that the charge pump output is inhibited if the two PD inputs are within +/- δ ns of each other in rising edge.