// PID controller model with differential input and single output


module pid(in1,in2,out);
 input in1,in2;
 output out;
 voltage in1,in2,out;

 parameter real kp=1,           // proportional coefficient
                ki=1,           // integral coefficient
                kd=1;           // differential coefficient
 real vin;

 analog
 begin
   vin = v(in1,in2)/2;
   v(out) <+ kp*vin + ki*idt(vin,0) + kd*ddt(vin);
 end
endmodule