Simulation issue with ideal relay implemented in verilog a

This probably depends on the rest of your circuit. I'd not seen the schematic until I clicked on the image - but what's happening is that the capacitor is being charged up (instantaneously, since there's no impedance) and then holding that voltage when the relay is open - because there's nothing to discharge it. Even if you ended up with a gmin resistor (which I don't think you do), that would be a time constant of 1s. Try adding a 10M resistor in parallel with the capacitor, and you'll then see it start to discharge during the off cycles.

I'd checked it with this circuit below and got the attached waveforms before I saw the picture:

//
v1 (sinin 0) vsource type=sine freq=5k ampl=1
v2 (clk 0) vsource type=pulse val0=0 val1=1 rise=1u fall=1u period=20u width=10u
I1 (clk 0 sinin sinout) SWITCH switch1=0.5
r2 (sinout 0) resistor r=100k

ahdl_include "SWITCH.va"

tran tran stop=200u

As you can see, it's working fine.

Regards,

Andrew.

Hello, 

I am trying to simulate NEM relay based inverter using verilog-a .  Please find the code below  

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

module OHMIC_CANTILEVER_RF_MEMS_SWITCH(s,d,g);  inout s, d, g;  electrical s, d, g;  kinematic z, velocity;

// Dimensions   parameter real g_0=0.6e-6 from (0:inf); // nominal gap height [m]  parameter real g_d=0.2e-6 from (0:inf); // nominal gap height minus dimple thickness [m]  parameter real l=75e-6 from (0:inf); // beam length [m]  parameter real t=5e-6 from (0:inf); // beam thickness [m]  parameter real w=30e-6 from (0:inf); // beam width [m]  parameter real W_c=10e-6 from (0:inf); // contact width [m]  parameter real W=10e-6 from (0:inf); // electrode width [m]  parameter real x=30e-6 from (0:inf); // beam anchor to electrode edge distance [m]  // Electrical parameters  parameter real R_c=1.0 from [0:inf); // contact resistance [Ohm]  // Material parameters: beam (gold)  parameter real rho=19.2e3 from (0:inf); // mass density [kg/m^3]  parameter real E=78e9 from (0:inf); // Young's modulus [Pa]  // Material parameters: gas (air):  parameter real lambda=1.5e-7 from [0:inf); // mean-free path [m]  parameter real mu=1.845e-5 from (0:inf); // viscosity coefficient [kg/(m.s)]  // van der Waals and nuclear force coefficients  parameter real c_1=10e-80 from [0:inf); // van der Waals force coefficient [N.m]  parameter real c_2=10e-75 from [0:inf); // nuclear force coefficient [N.m^8]

real A, b, C_ds, C_gs, C_u, F_c, F_e, F_s, f_m_0, I1, I2, IIP3, k_1, m, Q_e, Q_m, t_s_max, t_s_min, V_H, V_P, V_S;

analog begin

@ ( initial_step ) begin  A=W*w;  $strobe("\n%M: A (electrode area [m^2]) = %E",A);  m=0.4*rho*l*t*w;  $strobe("%M: m (effective beam mass [kg]) = %E",m);  k_1=2*E*w*pow(t/l,3)*(1-x/l)/(3-4*pow(x/l,3)+pow(x/l,4));  $strobe("%M: k_1 (spring constant [N/m]) = %E",k_1);  V_H=sqrt(2*k_1*(g_0-g_d)*pow(g_d,2)/(`P_EPS0*A));  $strobe("%M: V_H (hold-down voltage [V]) = %E",V_H);  V_P=sqrt(8*k_1*pow(g_0,3)/(27*A*`P_EPS0));  $strobe("%M: V_P (pull-in voltage [V]) = %E",V_P);  f_m_0=sqrt(k_1/m)/(2*`M_PI);  $strobe("%M: f_m_0 (mechanical resonant frequency [Hz]) = %E",f_m_0);  Q_m=(sqrt(E*rho)*pow(t,2)*pow(g_0,3))/(mu*pow(w*l,2));  $strobe("%M: Q_m (mechanical quality factor []) = %E",Q_m);  V_S=V_P;  t_s_max=27*pow(V_P,2)/(4*2*`M_PI*f_m_0*Q_m*pow(V_S,2));  $strobe("%M: t_s_max (maximum switching time [s], V_S = V_P) = %E",t_s_max);  t_s_min=3.67*V_P/(V_S*sqrt(k_1/m));  $strobe("%M: t_s_min (minimum switching time [s], V_S = V_P) = %E",t_s_min);  C_u=`P_EPS0*W_c*w/g_0;  $strobe("%M: C_u (up-state capacitance [F]) = %E",C_u);  IIP3=10*log(2*k_1*pow(g_0,2)/(`M_PI*10e9*pow(C_u*50,2)))+30;  $strobe("%M: IIP3 (third order intercept [dBm], C=C_u, delta_f < f_m_0, f=10 GHz, Z=50 Ohm) = %E",IIP3);  end

// b: damping coefficient [N.s/m] (displacement-compensated squeeze-film damping)  Q_e=Q_m*pow(1.1-pow(g_d*tanh(Pos(z)/g_d)/g_0,2),1.5)*(1+9.9638*pow(lambda/(g_0-g_d*tanh(Pos(z)/g_d)),1.159));  $strobe("\n%M: Q_e (displacement-compensated mechanical quality factor []) = %E",Q_e);  b=k_1/(2*`M_PI*f_m_0*Q_e);  $strobe("%M: b (damping coefficient [N.s/m]) = %E",b);

// Forces  F_c=c_1*W_c*w/pow(g_d-g_d*tanh(Pos(z)/g_d)+1e-9,3)-c_2*W_c*w/pow(g_d-g_d*tanh(Pos(z)/g_d)+1e-9,10);  $strobe("%M: F_c (attractive van der Waals and repulsive nuclear forces [N]) = %E",F_c);  F_e=`P_EPS0*A*pow(V(s,g),2)/2*1/pow(g_0-Pos(z),2);  //F_e=`P_EPS0*A*pow(V(s,g),2)/2*1/pow(g_0-g_d*tanh(Pos(z)/g_d),2); // Envelope simulation  $strobe("%M: F_e (electrostatic force [N]) = %E",F_e);  F_s=k_1*Pos(z);  //F_s=k_1*g_d*tanh(Pos(z)/g_d); // Envelope simulation  $strobe("%M: F_s (spring force [N]) = %E",F_s);

// Nonlinear state-space description  Pos(velocity):ddt(Pos(z))==Pos(velocity);  Pos(z):ddt(Pos(velocity))==1/m*(-b*Pos(velocity)-F_s+F_e+F_c+white_noise(4*`P_K*$temperature*b, "BROWNIAN_NOISE"));

C_ds=`P_EPS0*W_c*w/(g_0-Pos(z));  I1=ddt(C_ds*V(d,s));  I2=V(d,s)/R_c+white_noise(4*`P_K*$temperature/R_c, "JOHNSON_NYQUIST_NOISE_R_c");  if (Pos(z)<g_d)  I(d,s)<+I1;  else  I(d,s)<+I2;

C_gs=`P_EPS0*A/(g_0-Pos(z));  I(g,s)<+ddt(C_gs*V(g,s));

end

endmodule

 The testbench for simulation and output wavforms are attached below. I am not getting the correct output waveforms and I do not know why.  

Thank you in advance,

Marah

Hello, 

I am trying to simulate NEM relay based inverter using verilog-a .  Please find the code below  

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

module OHMIC_CANTILEVER_RF_MEMS_SWITCH(s,d,g);  inout s, d, g;  electrical s, d, g;  kinematic z, velocity;

// Dimensions   parameter real g_0=0.6e-6 from (0:inf); // nominal gap height [m]  parameter real g_d=0.2e-6 from (0:inf); // nominal gap height minus dimple thickness [m]  parameter real l=75e-6 from (0:inf); // beam length [m]  parameter real t=5e-6 from (0:inf); // beam thickness [m]  parameter real w=30e-6 from (0:inf); // beam width [m]  parameter real W_c=10e-6 from (0:inf); // contact width [m]  parameter real W=10e-6 from (0:inf); // electrode width [m]  parameter real x=30e-6 from (0:inf); // beam anchor to electrode edge distance [m]  // Electrical parameters  parameter real R_c=1.0 from [0:inf); // contact resistance [Ohm]  // Material parameters: beam (gold)  parameter real rho=19.2e3 from (0:inf); // mass density [kg/m^3]  parameter real E=78e9 from (0:inf); // Young's modulus [Pa]  // Material parameters: gas (air):  parameter real lambda=1.5e-7 from [0:inf); // mean-free path [m]  parameter real mu=1.845e-5 from (0:inf); // viscosity coefficient [kg/(m.s)]  // van der Waals and nuclear force coefficients  parameter real c_1=10e-80 from [0:inf); // van der Waals force coefficient [N.m]  parameter real c_2=10e-75 from [0:inf); // nuclear force coefficient [N.m^8]

real A, b, C_ds, C_gs, C_u, F_c, F_e, F_s, f_m_0, I1, I2, IIP3, k_1, m, Q_e, Q_m, t_s_max, t_s_min, V_H, V_P, V_S;

analog begin

@ ( initial_step ) begin  A=W*w;  $strobe("\n%M: A (electrode area [m^2]) = %E",A);  m=0.4*rho*l*t*w;  $strobe("%M: m (effective beam mass [kg]) = %E",m);  k_1=2*E*w*pow(t/l,3)*(1-x/l)/(3-4*pow(x/l,3)+pow(x/l,4));  $strobe("%M: k_1 (spring constant [N/m]) = %E",k_1);  V_H=sqrt(2*k_1*(g_0-g_d)*pow(g_d,2)/(`P_EPS0*A));  $strobe("%M: V_H (hold-down voltage [V]) = %E",V_H);  V_P=sqrt(8*k_1*pow(g_0,3)/(27*A*`P_EPS0));  $strobe("%M: V_P (pull-in voltage [V]) = %E",V_P);  f_m_0=sqrt(k_1/m)/(2*`M_PI);  $strobe("%M: f_m_0 (mechanical resonant frequency [Hz]) = %E",f_m_0);  Q_m=(sqrt(E*rho)*pow(t,2)*pow(g_0,3))/(mu*pow(w*l,2));  $strobe("%M: Q_m (mechanical quality factor []) = %E",Q_m);  V_S=V_P;  t_s_max=27*pow(V_P,2)/(4*2*`M_PI*f_m_0*Q_m*pow(V_S,2));  $strobe("%M: t_s_max (maximum switching time [s], V_S = V_P) = %E",t_s_max);  t_s_min=3.67*V_P/(V_S*sqrt(k_1/m));  $strobe("%M: t_s_min (minimum switching time [s], V_S = V_P) = %E",t_s_min);  C_u=`P_EPS0*W_c*w/g_0;  $strobe("%M: C_u (up-state capacitance [F]) = %E",C_u);  IIP3=10*log(2*k_1*pow(g_0,2)/(`M_PI*10e9*pow(C_u*50,2)))+30;  $strobe("%M: IIP3 (third order intercept [dBm], C=C_u, delta_f < f_m_0, f=10 GHz, Z=50 Ohm) = %E",IIP3);  end

// b: damping coefficient [N.s/m] (displacement-compensated squeeze-film damping)  Q_e=Q_m*pow(1.1-pow(g_d*tanh(Pos(z)/g_d)/g_0,2),1.5)*(1+9.9638*pow(lambda/(g_0-g_d*tanh(Pos(z)/g_d)),1.159));  $strobe("\n%M: Q_e (displacement-compensated mechanical quality factor []) = %E",Q_e);  b=k_1/(2*`M_PI*f_m_0*Q_e);  $strobe("%M: b (damping coefficient [N.s/m]) = %E",b);

// Forces  F_c=c_1*W_c*w/pow(g_d-g_d*tanh(Pos(z)/g_d)+1e-9,3)-c_2*W_c*w/pow(g_d-g_d*tanh(Pos(z)/g_d)+1e-9,10);  $strobe("%M: F_c (attractive van der Waals and repulsive nuclear forces [N]) = %E",F_c);  F_e=`P_EPS0*A*pow(V(s,g),2)/2*1/pow(g_0-Pos(z),2);  //F_e=`P_EPS0*A*pow(V(s,g),2)/2*1/pow(g_0-g_d*tanh(Pos(z)/g_d),2); // Envelope simulation  $strobe("%M: F_e (electrostatic force [N]) = %E",F_e);  F_s=k_1*Pos(z);  //F_s=k_1*g_d*tanh(Pos(z)/g_d); // Envelope simulation  $strobe("%M: F_s (spring force [N]) = %E",F_s);

// Nonlinear state-space description  Pos(velocity):ddt(Pos(z))==Pos(velocity);  Pos(z):ddt(Pos(velocity))==1/m*(-b*Pos(velocity)-F_s+F_e+F_c+white_noise(4*`P_K*$temperature*b, "BROWNIAN_NOISE"));

C_ds=`P_EPS0*W_c*w/(g_0-Pos(z));  I1=ddt(C_ds*V(d,s));  I2=V(d,s)/R_c+white_noise(4*`P_K*$temperature/R_c, "JOHNSON_NYQUIST_NOISE_R_c");  if (Pos(z)<g_d)  I(d,s)<+I1;  else  I(d,s)<+I2;

C_gs=`P_EPS0*A/(g_0-Pos(z));  I(g,s)<+ddt(C_gs*V(g,s));

end

endmodule

 The testbench for simulation and output wavforms are attached below. I am not getting the correct output waveforms and I do not know why.  

Thank you in advance,

Marah

Marah said:

I am not getting the correct output waveforms and I do not know why.

Me neither. I don't know what you're expecting the waveforms to look like because you didn't say - most likely it's because either your model is incorrectly modelling what you think you're modelling, or your expectations of what it's supposed to do are incorrect. 

I have absolutely no idea why you've posted on the end of a topic which has virtually no relationship to your question (other than being about Verilog-A). Your question is about a MEMS relay, whereas the original post was about a simple electrical switch. 

Also (and this is important) the Forum Guidelines clearly tell you not to post on the end of old threads, and to provide as much relevant data as you can.

Kindest Regards,

Andrew.