hi,

i am trying to build my vco modell using verilog-AMS in phase Domain laut paper of Kundert. But the problem is, that i can not verify the power of the flicker noise generated from flicker_noise() function. I found out that the phase noise, i have added to my vco, depends on the setting of noisefmax from the cadence analog environment. It does not depend on the power of the flicker_noise(power,n). I just want to find out the correct power of the flicker_noise(power,2) to adjust my accJitter*rdist_normal(seed,0,1) at the time domain of my vco model.

my code for the vco, that tests the flicker_noise

module VCO_VeriAMS (in,out,phase_out,gnd );
input in,gnd;
output out,phase_out;
electrical in,out,gnd,phase_out;


parameter real amp = 1;
parameter real Fmin=4.8G;
parameter real Fmax=5.2G;
parameter real Vmin=0.0;
parameter real Vmax=1.0;
parameter real accJitter=353.55f;
parameter real vco_gain = (Fmax-Fmin)/(Vmax-Vmin);
parameter real ttol=0.01*2/Fmax;
parameter real outStart=1/Fmin from[1/Fmin:inf);
parameter integer steps_per_period = 32;

electrical Wnoise;

  real phase,n;                  
  real inst_freq;            // instanteous frequency
  integer seed,fp;
  real diff,prev,now;

//assign out=n;

  analog begin

     @ ( initial_step ) begin
       seed=287;
       fp=$fopen("/tmp/periods.m");
     end


     inst_freq = Fmin+vco_gain*V(in,gnd);

     phase = idtmod(inst_freq,0,1);
     phase = phase+flicker_noise(accJitter*10G,2,"flicker_at_phasse");
     V(phase_out,gnd) <+ phase;
     @(cross(phase-0.25,1,ttol))
     begin
     if($abstime>=outStart) $fstrobe(fp,"%0.10e",$abstime-prev);
     prev=$abstime;
     end
     V(out)<+ amp*sin(2*`M_PI*phase);
  end

endmodule

In this case, I believe the exponent on the flicker noise should be 3 rather than 2.

-Ken

In phase domain models, the oscillation is suppressed.

-Ken

The way I deal with phase nosie in this phase domain model is backward-referring the noise to the tuning port, given the phase noise profile at an offset frequency. It works fine, but I am also wondering if lorenzian spectrum can be captured.

The way I tested is that:
1. use a white noise source to feed the tuning port. And in VCO model, the noise on the tuning port will be integrated and result in a phase fluctuation, phi_n(t).

2. Then pass "2*pi*fc*time+phi_n(t)" to cos function.
3. Ideally we will get the sinusoidal output with phase noise.

Somehow it works with closed-loop PLL simulation with PSS + Pnoise.

But what I found in free running VCO phase noise plot is that I cannot see lorenzian caused by sin (integral of white noise). The phase noise spectrum will keep going up with the lower offset freq.