What's wrong with my verilog-A model of the LPF?

[shaq]

Dear all,

Can you help me to check which part is wrong?
When I use the model of the 2nd order LPF in my PLL, it doesn't work.
Thanks for your help.

`include "disciplines.vams"
`include "constants.vams"

//  in-------------------out
//         |           |
//        Rs         Cp
//         |           |
//        Cs         |
//         |           |
//       gnd         gnd


module lpf_2 ( in, out );
inout in, out;
electrical in, out;
parameter real Rs=4.1e3 from (0:100e6),
                       Cs=30.6e-12 from (0:1),
                       Cp=1.92e-12 from (0:1);

analog
          V(out) <+ laplace_nd( V(in), {1, Cs*Cp}, {0, Cs+Cp, Cs*Cp*Rs} );

endmodule