Phase frequency detector and charge pump current!

[Mustahsin]

Hi,

I am using an IC where it has PLL integrated along with Phase Frequency detector. In the data sheet there are some rating about "Charge pump current". What this current mean? How can I physically interpret this current to my desired out put. Does it something to do with the speed of the loop?...how can I calculate that?

For your convenience,
1. Here are the link for IC: https://www.ti.com/lit/ds/symlink/cdce62002.pdf

2. Link for EVM Board of this IC: https://www.ti.com/lit/ug/scau034/scau034.pdf

3. Some basics about Charge pump with 4th order filter: **broken link removed**

Thanks in advance.

 

[D.A.(Tony)Stewart]

An internal charge pump with a cap is equivalent to an external integrator with a reference voltage equal to no phase error.


When the phase error is a pulse controlled current source going into capacitive load , they call it a charge pump or essentially an integrator. This is an essential part of the PLL to reduce steady state phase error to zero but tends to make it more unstable with delay. A series RC circuit gives proportional and integral gain improves this..

This current pump makes it easy to implement the classic PI part of a PID compensation feedback loop. Both of these give faster lock-in time with more bandwidth and reasonable jitter while having enough gain margin to remain stable. PLL tradeoffs must be chosen carefully to give desired characteristics of lock-in time and phase jitter.