I have a question regarding ac small-signal simulation with magnetic fields.  It may be more of a questio\
n concerning how Spectre actually works.  I have written a compact model in Verilog-A which successfully \
describes the dynamics of a magnetic nanoparticle (abbreviated code shown below - Theta(Mpol) and Theta(M\
az) are the polar and azimuthal angles of magnetization respectively).  I want to do an ac simulation to \
show ferromagnetic resonance at a particular frequency and have thus far been unsuccessful.  The stimulus\
is the ac field and a DC bias field, both in the z-dir (perpendicular to the material plane), because I \
would like to see the magnetization rotate about the z-axis.  The simulation runs but the output is extre\
mely small (zero really...) and without any resonant peak at the expected frequency.

I'm wondering if there is a reason why the small-signal analysis would not work with the system of equati\
ons I have developed for this magnetic system (I realize that I might not have yet all of the conditions \
just right to get a reasonable output).  I had assumed that since I had a DC operating point from other t\
ransient simulations, Spectre would linearize the system of equations around that operating point in the \
same way that SPICE does. I don't think it should matter whether the system uses V and I or M and H - Doe\
s anyone know if there is a limitation to the kind of system in which a Spectre ac analysis can operate? \
Does anyone know if Spectre really does do a differential linearization of the system equations in the s\
ame way SPICE does?

Thank you,
Linda

(partial code listing)
-----------------------------
nature Magnetic_Induction
       abstol = 1e-6 ;
       access = H ;
       units = "A/m" ;
endnature

discipline sig_flow_H
       potential Magnetic_Induction ;
enddiscipline

module SW3D(hx, hy, hz,Mpol,Maz,Mea );
input hx, hy, hz ;
inout Maz, Mpol, Mea ;

sig_flow_H hx, hy, hz, hMpol, hMaz ; // H-field vector components
rotational  Mea, Maz, Mpol, Anis; // port discipline for easy axis angle
                                              // and magnetization angles(spherical)
  :
//parameters set
  :
analog begin
  :
 H(hMpol) <+ ....eqn for H(hMpol)....
 H(hMaz)  <+ ....eqn for H(hMaz)...

 Theta(Mpol) <+ idt((C1*G0)*(H(hMaz) + alpha*H(hMpol)),`M_PI/2 ) ;

 Theta(Maz) <+ idt(((C1*G0)/sin(Theta(Mpol)))*(alpha*H(hMaz)- H(hMpol)),`M_PI);
end
endmodule

Ken,
Yes,  I did apply the small signal stimulus, at least I believe I did it correctly.  I use currents as inputs to generate magnetic fields via the behavioral expression: H = I/2w (w is the trace width).   I put a DC current source (idc) in parallel with a sinewave current source (isin) both from the analogLib.  The idc magnitude is 6mA (this is a small-moderate field strength effective for my system).  However, I am confused about the ac source.  The edit-object-properties box for isin asks for:
1) an AC magnitude  ->  which I set to 200uA (pk-pk swing)
2) a DC current -> which I set to 6mA, just like the parallel idc source  <= is this a problem?
3) an "Amplitude" -> which I set to 100uA <= I assume this is the Peak amplitude?

I have searched through the Spectre Users guide and the Spectre reference for what these object properties mean, and can not find them.  Can I use just  the isin source, without the idc source since I can specify a DC source value in isin? Am I using the AC magnitude and Amplitude options correctly - what Cadence manual talks about the object property settings?

I saw that you have written a book on Spectre and Spice.  In this book do you explain how these tools linearize and solve circuit equations?  If it is not something that you address, can you cite a reference that does?

Appreciatively,
Linda

The  netlist is attached.

Thank you for looking at this.
Linda