Verilog-A switch model with thermal noise modeling

Hello,

I am trying to write a verilog-A model for an ideal switch that would be compatible with PSS/PNOISE simulations. 

The goal is to simulate kT/C noise in switched-capacitor circuits, so I have the switch's ON-resistance as a parameter, and I would need to also model the Ron's equivalent thermal noise when the switch is on.

The simple code below should theoretically meet that need, according to what I have read. Unfortunately, simulation results from a PSS/PNOISE analysis performed on a simple track-and-hold circuit using this code look like garbage...

If I remove the white noise term at the end of the listing, and insert resistors from analogLib in series with every switch at the schematic level, the results look OK.

I could of course do that, but I am looking for a more elegant solution, one that has thermal noise embedded within the switch model itself.

Can you please help ?

Best regards,

Marc

`include "discipline.h"
`include "constants.h"

module vA_sw1(A,B,G);

inout A, B;
input G;
electrical A, B, G;

parameter real supply=3.0, Ron=10k;

analog begin

@(cross(V(G)-supply/2, 1));
@(cross(V(G)-supply/2, -1));

I(A,B) <+ (V(G) > supply/2) * (V(A,B)/Ron + white_noise(4 * `P_K * $temperature / Ron, "thermal"));

end

endmodule