About Connection for switched Capacitor in LPF of PLL

[gyamwoo]

Hi everyone,

I use switched capacitor banks in LPF so that I can modify the loop bandwidth for PLL.
However, I am wondering what the connection of switched capacitor is right...

There are 2 kind of connection for switched Cap below. Most of design I seen is Type B.
But I'd like to choose Type A because pass is connect to gnd and Vctrl is connected directly to Cap.
Could anyone tell me if there would be any problem I don't know??

Sincerely,
Gyamwoo

Transmission gate (pass) is used to realize a switch, and mos varactor used for Cap.
Type A: (Ignore these dots, pls )
Vctrl-----+-----+
.............|.......|
...........Res.....|
.............|.......|
...........Cap...Cap
.............|.......|
...........pass....|
.............|.......|
gnd------+-----+


Type BIgnore these dots, pls )
Vctrl-----+-----+
.............|.......|
...........Res.....|
.............|.......|
...........pass..Cap
.............|.......|
............Cap....|
.............|.......|
gnd------+-----+

 

[FvM]

I guess for an IC implementation you'll prefer a grounded MOS capacitor, thus use B.