How to generate Ic in a CPPLL?

[christon]

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 ^_^

 

[icsoul]

what's your mean?

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

 

[christon]

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?

 

[needforspeed]

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.

 

[christon]

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.

 

[colombo2]

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

 

[jecyhale]

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 ^_^

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.