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How to get transfer of PFD as function of input phase error

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Alles Gute

Full Member level 2
Dec 4, 2003
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As shown in the figure is the transfer of the classical three state PFD as a function of the input phase error.
My question is How to get this curve by simulation? I want to know this because I want to design a new PFD and I need to shown the transfer curve.

Re: How to get transfer of PFD as function of input phase er

It is a little tricky!

The problem is that theinitial state is very important. I know only to get either positive or negative phase domains in a single simulation. If you want to have a phase resolution of


you need to take a frequency difference of 1/256. Because the phase frequency detector signal is integrated with the help of the chargepump you need to integrate the ouput pulse. You have to sample the integration result just before the rising edge of the faster frequency. The take the difference between two samples in sequence. So in effect the sampled signal is a time discrete signal with a phase resolution of 2*pi/256. The first sample for the phase difference zero should give a zero integral. If the phase difference is greater than 2*pi you will see the typical effect of frequency selectivity.

The reduction of phase range because of the minimum pulse time could also be observed.

Re: How to get transfer of PFD as function of input phase er

sweep the input phase differece, measure the difference of output charge or voltage depending on your plot y-axis

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