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Design >> Mixed-Signal Design >> Normalized phase noise the PLL
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Message started by dpienkow on Jul 6^th, 2007, 6:54am

Title: Normalized phase noise the PLL
Post by dpienkow on Jul 6^th, 2007, 6:54am

Hello Experts,

I am designing now the charge pump with phase detector for the PLL.
At the moment I measure the phase noise at the output of the charge pump and observe the levels around -120 dBc @ 1kHz offset. Comparison frequency is 50 kHz.
I do knot know, if it is good, very good or maybe poor result. Therefore, I would like to compare myself with state of the art circuit from National or Analog.
They specify normalized phase noise for the PLL, which as far I understand should be the phase noise at the output of the charge pump.

To compute total noise of the closed loop PLL, both companies give the equation
PNtotal=PNpll+10*log(Fcomp)+20*log(N),

where PNpll is what I am interested in.

This formula suggest, that decreasing the comparison frequency in my simulations will decrease the phase noise.
It is not the case in my simulation.
Therefore I would like to ask you, how to compute (simulate) this normalized phase noise?

Best Regards,
Dariusz Pienkowski