Phase Shift Filter Simulation Question

Hi all,

I am using an example from Hspice manual to study how to simulate a phase shift register. In the given example, Hspice is using G-element to model the phase shift register. According to the manual, it is using circular convolution to calculate the output response of the G-element. The netlist from the manual is as following:

.tran 0.1n 300n
.options post=2 ingold=2 accurate
Vctrl ctrl gnd sin (0 1 10e6)
Gtest gnd test freq ctrl gnd
+ 1.0e00 0 30
+ 1.0e01 0 30
+ 1.0e02 0 30
+ 1.0e03 0 30
+ 1.0e04 0 30
+ 1.0e05 0 30
+ 1.0e06 0 30
+ 1.0e07 0 30
+ 1.0e08 0 30
+ 1.0e09 0 30
+ 1.0e10 0 30
+ MAXF=1.0e9 DELF=10e6
Rtest test gnd 1
.end

Basically, what the examples does is to shift the control input voltage (sine wave) by 30 degree. I am trying to do hand-calculation so that I understand the theory behind the simulation. I tried to use inverse DFT to transform the frequency response given in the above frequency table to get its time domain response. Then, at each time point, I am performing circular convolution between the input voltage and the time domain response. But, I just couldn't get the simulation result from Hspice. Does anyone have clue the calculation performed by Hspice?
Thank you for looking at my question.

SFguy