How to reduce the current mismatch in PFD and CP blocks of a PLL?

时间：04-09 整理：3721RD 点击：

I designed a Phase-Frequency-Detector and an Charge-Pump, as blocks of a PLL.
And what parameters I should measure of this two blocks?
The mismatch of Iup and Idn and the stability of the CP?
And anymore?

About the current mismatch, what method I should use?
The method I used is to connect a dc voltage source with the CP output, and make dc sweep of this source from 0 to VDD when only Iup and Idn is working, is it right?

Hi, jecyhale,
Thank you!
Can you tell me how to simulate the glith of CP when switchs on/off?
My reference frequency is 1MHZ, and I use the pulse source with the period is 1us,
the duty cycle is 50%, and the up and dn source have 50ns difference in time domain, the result is that only Iup or Idn is working in the 50ns, Is this method right?
Yes, I use the high swing cascode current mirror as the current source.
It can reduce the current mismatch.
And you should simulate the glith of CP when the switch is on/off.
Besides, you can simulation the highest operation frequency of PFD.

please clarify if during simulation for current mismatch only one (UP?DN) or both are active

Yes, I use the high swing cascode current mirror as the current source.
It can reduce the current mismatch.
And you should simulate the glith of CP when the switch is on/off.
Besides, you can simulation the highest operation frequency of PFD. I think Iup and Idn will both work for some hundred ps to eliminate the dead zone of the PFD.

Yes, I use the high swing cascode current mirror as the current source.
It can reduce the current mismatch.
And you should simulate the glith of CP when the switch is on/off.
Besides, you can simulation the highest operation frequency of PFD. You can connect the two input of PFD both to 1MHz, then run the transient simulation, and to view the current flowing through each switch.

If the input of PFD is same, the Iup and Idn will be on/off at the same time.
and the glitch of ouput current to loop filter should be the less the better.