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How to increase the precision of signal [Verilog-A problem]?

YYLee

I used the compare operator ">" to detect the value that higher than a threshold.

But the value is undesirable ...

For example, the following is code, and the input signal AVDD5 (rising from 0 to 5V):

$display("-------------AVDD5: ", V(AVDD5));
   if(V(AVDD5) > 0.72 && V(AVDD5) < 0.73)begin
       $display("-----------[range]--AVDD5: ", V(AVDD5));
   end
   else if(V(AVDD5) > 0.73 && V(AVDD5) < 0.84) begin
        [do something]
   end

       [do something]
   else begin

   end

The result is 

-------------AVDD5: 0.0063628

-------------AVDD5: 0.0203494

-------------AVDD5: 0.0651065

-------------AVDD5: 0.208329

-------------AVDD5: 0.666642

-------------AVDD5: 1.16764

-------------AVDD5: 1.66865

-------------AVDD5: 2.16965

-------------AVDD5: 2.19

-------------AVDD5: 2.25513

As the mark position, i need the range [0.72, 0.73], [0.73, 0.84]

But the time range is too big (0.666666 -> 1.16764), so the if statement couldn't catch it!

Could anyone help me, thank for you a lot!!!!!

Parents
  • Andrew Beckett

    OK, you appear to have edited the post after first submitting it. Anyway, I think what you're saying is that it doesn't trigger those if statements because the change is too rapid. That's because an if() statement doesn't force a timestep in the simulator - and so if the simulator tolerances can be met anyway, it could easily have successive time steps at 0.666 and then 1.67V. If you want to guarantee accurate transitions into each region, you would use the @cross() function to trigger the crossing point. You don't necessarily need to have this in the action of the @cross, you could just do:

    @cross(V(AVDD5)-0.72);
    @cross(V(AVDD5)-0.73);
    @cross(V(AVDD5)-0.84);

    bear in mind though that this will slow down the simulation (if there are a lot of crossings) as it has to take time steps to resolve the crossing point and take additional time steps - you need to determine how accurately you need to resolve this. 

    Andrew

Reply
  • Andrew Beckett

    OK, you appear to have edited the post after first submitting it. Anyway, I think what you're saying is that it doesn't trigger those if statements because the change is too rapid. That's because an if() statement doesn't force a timestep in the simulator - and so if the simulator tolerances can be met anyway, it could easily have successive time steps at 0.666 and then 1.67V. If you want to guarantee accurate transitions into each region, you would use the @cross() function to trigger the crossing point. You don't necessarily need to have this in the action of the @cross, you could just do:

    @cross(V(AVDD5)-0.72);
    @cross(V(AVDD5)-0.73);
    @cross(V(AVDD5)-0.84);

    bear in mind though that this will slow down the simulation (if there are a lot of crossings) as it has to take time steps to resolve the crossing point and take additional time steps - you need to determine how accurately you need to resolve this. 

    Andrew

Children
  • YYLee
    in reply to Andrew Beckett

    Thank you! Andrew, I solved the problem with @cross. It is important concepts for me!

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