module qam16(in,out);
 input [0:3] in;
 output out;
 voltage in,out;

 parameter real freq = 1.0 from (0:inf);
 parameter real ampl = 1.0, thresh = 2.5;
 parameter real tdelay = 0 from [0:inf),
                ttransit = 1/freq;

 real x,y,phi;
 integer row,col;

 analog
 begin
   row = 2*(V(in[3]) > thresh + V(in[2]) > thresh);
   col = 2*(V(in[1]) > thresh + V(in[0]) > thresh);

   x = transition(row-1.5,tdelay,ttransit);
   y = transition(col-1.5,tdelay,ttransit);

   phi = 2 * `M_PI * freq * $realtime();
   V(out) <+ ampl * (x * cos(phi) + y * sin(phi));
 end
endmodule