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Fatal error found by spectre during topology check.

Aswathyn

I am trying to build verilogA code of MTJ in cadence. I got the following error. I am new to cadence . please help me to eliminate the error . 

Fatal error found by spectre during topology check.
FATAL: The following branches form a loop of rigid branches (shorts) when added to the circuit:
I1:mz_flow (from net012 to 0)
I1:my_flow (from net14 to 0)
I1:mx_flow (from net13 to 0)

the schematic used is given below

Parents
  • Andrew Beckett

    There's no chance of debugging this without seeing:

    1. The Verilog-A code for MTJ . I assume this is a "Magnetic Tunnel Junction" but that's a bit of a guess; you might want to expand when using unusual acronyms. That said, even knowing that wouldn't help without seeing the code
    2. What's inside the Initial block too - is that Verilog-A?

    It suggests that both have a voltage source (or a current probe) and for each of the mx, my,mz pins and hence you've got two voltage sources in parallel, which leads to something that cannot be solved (it's impossible to solve the simultaneous equations when you have two ideal voltage sources cannot be in parallel).

    Regards,

    Andrew

  • Aswathyn
    in reply to Andrew Beckett

    Fullscreen initial (1).txt Download 
    // VerilogA for Betty_Jan2018, Initial, veriloga

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

module Initial(x,y,z);

//VerilogA code to set the initial state of magnetization vector:
electrical x,y,z;
integer seed;
real RandomTheta, volume, std_dev;
parameter real kb = 1.38e-16 from (-inf:inf);//Boltzmann’s constant
parameter T = 300 from (-inf:inf);//Temperature
parameter real Ms = 1050 from (0:inf);
parameter real Hk = 250 from (0:inf);
parameter real length = 60e-7 from (0:inf);
parameter real width = 60e-7 from (0:inf);
parameter real thickness = 1e-7 from (0:inf);
analog begin
volume = length*width*thickness;
std_dev=sqrt(kb*T/(Ms*volume*Hk));//standard deviation of theta
if(analysis("ic"))
begin
//This defines the initial conditions for the magnetization vector
//fixed
/*V(x) <+ 0;
V(y) <+ 0.3;
V(z) <+ sqrt(1 - 0.3*0.3);*/
//random
seed=4;
RandomTheta=$rdist_normal(seed, 0, std_dev);
V(x) <+ 0.2;//0;
V(y) <+ 0.45;//sin(RandomTheta);
V(z) <+ 0.65;//cos(RandomTheta);
end
else if(analysis("tran")) begin
end
end
endmodule

  • Aswathyn
    in reply to Aswathyn

    Fullscreen mtj_model (1).txt Download 
    // VerilogA for Betty_Jan2018, MTJ, veriloga

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

module MTJ_Model(pos, neutral, neg, mx, my, mz);
//terminal definitions
inout pos,neutral,neg, mx, my, mz;
electrical pos,neutral,neg;
electrical mx, my, mz;
branch (pos, neutral) top;
branch (neutral, neg) bott;
// variables
real top_res0, top_res, bott_res0, bott_res, net_torque,polarization_top, polarization_bott, top_efficiency, bottom_efficiency,
volume, rpar_top, rpar_bott, RandomGaussian, Hfluctuation;
integer seed;
// LLG equation coefficients
real h1, h2, h3, k1, k2, k3, s1, s2, s3;
// model parameters
parameter integer use_as_dmtj = 1 from (-2:2);
parameter real plank_constant = 1.054e-27 from (-inf:inf);
parameter real electron_charge = 1.602e-19 from (-inf:inf);
parameter real gyromagnetic_ratio = 1.7608e7 from (-inf:inf);
parameter real alpha = 0.002 from (0:inf);
parameter real Ms = 1050 from (0:inf);
parameter real Hk = 250 from (0:inf);
parameter real Vh = 0.5 from (0:inf);
parameter real Rp = 1500 from (0:inf);
parameter real tmr = 2 from (0:inf);
parameter real length = 60e-7 /*60e-7*/ from (0:inf);
parameter real width = 60e-7 from (0:inf);
parameter real thickness = 1e-7 from (0:inf);
parameter real tox = 1.2e-9 from (0:inf);
parameter real kb = 1.38e-16 from (-inf:inf);//Boltzmann’s constant
parameter T = 300 from (-inf:inf);//Temperature
parameter real PI = 3.14 from (0:inf);
// model analog block
analog begin
volume = length*width*thickness;
k1 = -1*gyromagnetic_ratio/(1 + pow(alpha,2));
k2 = -1*gyromagnetic_ratio*alpha/(1 + pow(alpha,2));
k3 = gyromagnetic_ratio*plank_constant/(2*electron_charge*Ms*volume);
//conventional STT source (PL with easy axis parallel to FL)
s1 = 0;
s2 = 0;
s3 = 1;
rpar_top = 2*Rp*(tmr + 1 + V(top)*V(top)/(Vh*Vh))/(tmr + 2*(1 + (V(top)*V(top))/(Vh*Vh)));
rpar_bott = 2*Rp*(tmr + 1 + V(bott)*V(bott)/(Vh*Vh))/(tmr + 2*(1 + (V(bott)*V(bott))/(Vh*Vh)));

polarization_top = sqrt(tmr/(tmr + 2*(1 +V(top)*V(top)/(Vh*Vh))));
polarization_bott = sqrt(tmr/(tmr + 2*(1 + V(bott)*V(bott)/(Vh*Vh))));
top_efficiency = polarization_top/(2*(1 + pow(polarization_top,2)*V(mz)));
bottom_efficiency = polarization_bott/(2*(1 + pow(polarization_bott,2)*V(mz)));
top_res = rpar_top/(1 + polarization_top*polarization_top*V(mz));
bott_res = 0;
net_torque = I(top)*top_efficiency;
//Heff=Heff+Hfluctuation
seed=25;
RandomGaussian=$rdist_normal(seed, 0, 1);
Hfluctuation=sqrt(2*alpha*kb*T/(gyromagnetic_ratio*Ms*volume))*RandomGaussian;
h1= -4*PI*Ms*V(mx)+Hfluctuation;
h2 = 0+Hfluctuation;
h3 = Hk*V(mz)+Hfluctuation;
if(analysis("ic"))
begin
end
else if(analysis("tran")) begin
V(mx):
ddt(V(mx)) == k1*(h3*V(my) - h2*V(mz)) + k2*(-h1*V(my)*V(my)- h1*V(mz)*V(mz) + h2*V(mx)*V(my) + h3*V(mx)*V(mz))+k3*net_torque*(-s1*V(my)*V(my) -s1*V(mz)*V(mz) + s2*V(mx)*V(my)+ s3*V(mx)*V(mz));
V(my):
ddt(V(my)) == k1*(h1*V(mz) - h3*V(mx))+ k2*(h1*V(mx)*V(my)- h2*V(mx)*V(mx) - h2*V(mz)*V(mz) + h3*V(my)*V(mz)) +k3*net_torque*(s1*V(mx)*V(my) - s2*V(mx)*V(mx) - s2*V(mz)*V(mz)+ s3*V(my)*V(mz));
V(mz):
ddt(V(mz)) == k1*(h2*V(mx) -h1*V(my))+ k2*(h1*V(mx)*V(mz)+ h2*V(my)*V(mz) -h3*V(mx)*V(mx) - h3*V(my)*V(my))+k3*net_torque*(s1*V(mx)*V(mz) + s2*V(my)*V(mz) - s3*V(mx)*V(mx)- s3*V(my)*V(my));
end
V(top) <+ I(top)*top_res;
V(bott) <+ I(bott)*bott_res;
end

endmodule

Reply
  • Aswathyn
    in reply to Aswathyn

    Fullscreen mtj_model (1).txt Download 
    // VerilogA for Betty_Jan2018, MTJ, veriloga

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

module MTJ_Model(pos, neutral, neg, mx, my, mz);
//terminal definitions
inout pos,neutral,neg, mx, my, mz;
electrical pos,neutral,neg;
electrical mx, my, mz;
branch (pos, neutral) top;
branch (neutral, neg) bott;
// variables
real top_res0, top_res, bott_res0, bott_res, net_torque,polarization_top, polarization_bott, top_efficiency, bottom_efficiency,
volume, rpar_top, rpar_bott, RandomGaussian, Hfluctuation;
integer seed;
// LLG equation coefficients
real h1, h2, h3, k1, k2, k3, s1, s2, s3;
// model parameters
parameter integer use_as_dmtj = 1 from (-2:2);
parameter real plank_constant = 1.054e-27 from (-inf:inf);
parameter real electron_charge = 1.602e-19 from (-inf:inf);
parameter real gyromagnetic_ratio = 1.7608e7 from (-inf:inf);
parameter real alpha = 0.002 from (0:inf);
parameter real Ms = 1050 from (0:inf);
parameter real Hk = 250 from (0:inf);
parameter real Vh = 0.5 from (0:inf);
parameter real Rp = 1500 from (0:inf);
parameter real tmr = 2 from (0:inf);
parameter real length = 60e-7 /*60e-7*/ from (0:inf);
parameter real width = 60e-7 from (0:inf);
parameter real thickness = 1e-7 from (0:inf);
parameter real tox = 1.2e-9 from (0:inf);
parameter real kb = 1.38e-16 from (-inf:inf);//Boltzmann’s constant
parameter T = 300 from (-inf:inf);//Temperature
parameter real PI = 3.14 from (0:inf);
// model analog block
analog begin
volume = length*width*thickness;
k1 = -1*gyromagnetic_ratio/(1 + pow(alpha,2));
k2 = -1*gyromagnetic_ratio*alpha/(1 + pow(alpha,2));
k3 = gyromagnetic_ratio*plank_constant/(2*electron_charge*Ms*volume);
//conventional STT source (PL with easy axis parallel to FL)
s1 = 0;
s2 = 0;
s3 = 1;
rpar_top = 2*Rp*(tmr + 1 + V(top)*V(top)/(Vh*Vh))/(tmr + 2*(1 + (V(top)*V(top))/(Vh*Vh)));
rpar_bott = 2*Rp*(tmr + 1 + V(bott)*V(bott)/(Vh*Vh))/(tmr + 2*(1 + (V(bott)*V(bott))/(Vh*Vh)));

polarization_top = sqrt(tmr/(tmr + 2*(1 +V(top)*V(top)/(Vh*Vh))));
polarization_bott = sqrt(tmr/(tmr + 2*(1 + V(bott)*V(bott)/(Vh*Vh))));
top_efficiency = polarization_top/(2*(1 + pow(polarization_top,2)*V(mz)));
bottom_efficiency = polarization_bott/(2*(1 + pow(polarization_bott,2)*V(mz)));
top_res = rpar_top/(1 + polarization_top*polarization_top*V(mz));
bott_res = 0;
net_torque = I(top)*top_efficiency;
//Heff=Heff+Hfluctuation
seed=25;
RandomGaussian=$rdist_normal(seed, 0, 1);
Hfluctuation=sqrt(2*alpha*kb*T/(gyromagnetic_ratio*Ms*volume))*RandomGaussian;
h1= -4*PI*Ms*V(mx)+Hfluctuation;
h2 = 0+Hfluctuation;
h3 = Hk*V(mz)+Hfluctuation;
if(analysis("ic"))
begin
end
else if(analysis("tran")) begin
V(mx):
ddt(V(mx)) == k1*(h3*V(my) - h2*V(mz)) + k2*(-h1*V(my)*V(my)- h1*V(mz)*V(mz) + h2*V(mx)*V(my) + h3*V(mx)*V(mz))+k3*net_torque*(-s1*V(my)*V(my) -s1*V(mz)*V(mz) + s2*V(mx)*V(my)+ s3*V(mx)*V(mz));
V(my):
ddt(V(my)) == k1*(h1*V(mz) - h3*V(mx))+ k2*(h1*V(mx)*V(my)- h2*V(mx)*V(mx) - h2*V(mz)*V(mz) + h3*V(my)*V(mz)) +k3*net_torque*(s1*V(mx)*V(my) - s2*V(mx)*V(mx) - s2*V(mz)*V(mz)+ s3*V(my)*V(mz));
V(mz):
ddt(V(mz)) == k1*(h2*V(mx) -h1*V(my))+ k2*(h1*V(mx)*V(mz)+ h2*V(my)*V(mz) -h3*V(mx)*V(mx) - h3*V(my)*V(my))+k3*net_torque*(s1*V(mx)*V(mz) + s2*V(my)*V(mz) - s3*V(mx)*V(mx)- s3*V(my)*V(my));
end
V(top) <+ I(top)*top_res;
V(bott) <+ I(bott)*bott_res;
end

endmodule

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