Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

discussion about PLL when input reference clock is high

Status
Not open for further replies.

jfyan

Full Member level 2
Joined
May 3, 2006
Messages
145
Helped
26
Reputation
52
Reaction score
4
Trophy points
1,298
Location
shanghai,china
Activity points
2,064
hi all,
i want to know what will happen to PLL's performance when input reference clock is high about 100-500MHz.
for example, as i observed, when the input clock is about 200MHz, the static phase error is very small, less than 10ps. and some other the bad effects such as leakage currents, mismatch in charge pump currents, can be smaller compared with low input clock, right?
what else i want to discuss is dead zone, i find it is a very big problem, and i think because of dead zone, the control voltage to the vco is random walking when the loop is in "locking". i don't know whether above are right? so let's have a hot talk.

good luck
jeff
 

Having higher reference frequency gives you the ability to choose a larger loop bandwidth .This can be good for the settling time (can have shorter settling time) and the high pass filtering effect of the VCO noise .The other noises however will have larger contribution .I'm not sure about its effect on charge pump mismatch and leakage current and I believe that it's very small (not sure) .

Concerning the dead zone, its effect will be more severe at higher reference frequencies .A nice solution would be to delay the output of the (N)AND gate of the reset of the FFs of the PFD with an amount that is higher than the dead zone delay .This would be sufficient to remove the dead zone .
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top