How to generate Ic in a CPPLL?

Status
Not open for further replies.
C

christon

Newbie level 4
Joined
Jul 25, 2008
Messages
7
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,321
generate ic

Hi,

I want to know how to generate charge/discharge current Ic in a CPPLL?
Use a bandgap? I think it will take up a large size.
A simple supply-independent bias current can vary more than twice in worst case, and it may cause instability?
Any other solution?

Thanks in advance ^_^
 

what's your mean?

In a CPPLL, the current is always generated by the charge pump.
 

Thanks.
Yes, the current Ic is generated by the charge pump, but I want to know where does Ic copy from? I mean how to generate the bias current for charge pump?
 

These is no on chip current reference which can generate process-independent current. I think you should make sure that your PLL is stable in different corners. Or you can employ a external resistor to adjust the charge pump current.
 

needforspeed,
You got it, I must keep my PLL stable in different corners , different reference frequency, and the full range of integer N in feedback divider.
Yes, I have read many datasheets and found an external resister is usually employed to generate Ic.
 

it depends on the temperature slope you want to get. it can come from a poly-current or PTAT but usually a poly current is used
 


I think you'd better use a constant current source of it with Band-gap and iPTAT.

Ibg=(Vref/R)
30% iPTAT plus 70% Ibg.

It will be constant with tempreture in some range.
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…