PLL design question (value of Icp??)

pll design mathcad

Hi.


I am working this days on a CP-PLL FS designed for Bluetooth and It is my first design

I have put the parameter value of each block but until now I can't determined the value of CP current (Icp)

How I can determined Its value??

Regards,

Salem

icp pll

If you are designing the part, then you can choose the Icp that you want. If you make it too large, then the loop filter capacitances will be very big. If you make Icp too small, then the thermal noise will be large in comparison, and you will have a noisy pll. Try using somewhere between 500 uA and 1 mA and you will be in a reasonable range.


Dave

RFDave said:

If you are designing the part, then you can choose the Icp that you want. If you make it too large, then the loop filter capacitances will be very big. If you make Icp too small, then the thermal noise will be large in comparison, and you will have a noisy pll. Try using somewhere between 500 uA and 1 mA and you will be in a reasonable range.


Dave

Click to expand...

Thanx Dave

I am designing the all system

I need an equation to determined this parameter related to the power or the noise or the speed any equation I can design with it like the other parameter (i.e. the loop bandwidth)

OR Do you mean , I have to only try all the values in the range and with the simulation I got the best performance ????

i.e : I am using 0.18um TSMC

Salem

the charge pump current determines the gain of the PLL , and it will also dtermine the speed of lock and so on , so u need to optimize it

also the high current in charge pump will make the mismatch in charge pump current is significant

u need to optimize the ICP , in modern designs the charge pump current is programmable

khouly

Well, charge pump current is a factor in the open and closed loop performance, but the VCO gain, loop division ratio, and loop filter components all come into play here. There really isn't a single equation that relates the charge pump current to lock time, phase noise, etc. Since all of these parameters are multiplied together, you can adjust things to compensate for other thing, and you can adjust the loop filter components to compensate for changes in the other loop parameters.

For a charge pump, I'd have to say that

1-up/down mismatch
2-leakage current
3-Dead Zone
4-Current output noise

are perhaps more important than the exact value of the charge pump current. It sounds like you need to spend some time looking at the linear, closed loop performance to get a better understanding of the trade off's.

If you have access to MathCAD, you might want to download Lance Lascari's MathCAD PLL worksheets and get a better understanding of the trade off's.

http://tools.rfdude.com/ is the link.

If you don't have MathCAD, I'm in the process of writing a PLL tool in Excel, that's located at www.keystoneradio.com/?n=Main.PLLDesign. It's not quite done yet, but it may be useful.

Dave

Depending on your loop gain design. try a matlab simulation.

Assalaamo alaykom,

Search www.National.com for a PLL system design tool..
also, check this thread, it's about almost the same issue..


It can be obtained for free..
Also, follow Dave's Excel sheet, i trust him as an expert

Regards,
Ahmad,

trade off between area and noise; larger Icp means larger loop filter cap, smaller Icp means larger noise, also , its value affects the loop gain and so affects poles & zeros positions, you might want a certain pole at certain postion for spur attenuation , i think Icp may have values between 1 uA to 1 mA depends on applications

As for Bluetooth (low power standard), I do recommend to allow Icp to be within 10u to 700u ..

Trials and errors method to design your system may also simplify your design flow within the above given (from experience) limit.

Descripe your system in an m-file function, and regularly test your components parameters untill reaching the best performance requested in the standard you work in.

Best wishes
Ahmad,