i am using spectre ,
my ref frequency is 5MHz
and i am ploting Iav v's phase error
i tried the delays before with the up and dn and it gives results till a certain limilts
but it did not give me my spec
i need to know the limitations on the delay which actually is related to fref
is there any limitations??
thanks for reply
1.fref and fvco is the two input of PFD.
2.let fref and fvco is the same frequnecy and the same phase, in your case that's 5MHz.
3.run .tran about 5 cycle.
4.measure the up and dn pulse width of PFD output.
5.the pulse width of 4 is called idle pulse.
6.if the idle pulse can turn on the charge pump, then you eliminate the dead zone problem.
Is that clear ?
no he means the pulse width in step 4 and not 4 pulses.now i can make something clear.the dead zone depends on the critical path in the pfd u use.naturally when the phase difference between the input and reference becomes smaller than this delay.then naturally the pfd is not going to output any signal.dead zone cannot be eliminated but only minimized.u can also try using a dynamic logic pfd.
amarnath said:In case of a pfd designed using nand gates ,it has a very long critical path.so any pulse width smaller than this delay cannot be generated.hope iam clear.
rfsystem said:eng_Semi,
it is not which one is dominant. It is the non-appropriate relation between minimum pulse time of the detector and the rise/fall time of the pump current.
There is no dead time in the detector! There is no dead time in the pump! If you simulate the charge over time/phase difference the resulting curve is looking like to have a dead zone.
The PFD operate only on one rising or falling edge of the inputs. It is edge triggered. The linearity performance will be impacted by the opposite edge if the pulse time is equal to the actual time/phase difference
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