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Accuracy of CROSS() function in Verilog-A

RFStuff

Dear All,

I am using cross() in verilog-A as below:-

 

vtol=1e-12;

@(cross(phase-10u,+1,ttol,vtol)) begin
       $strobe("TIME = %rs \n", $abstime);
     end

But when I checked the abstime, it is NOT exactly at 10u of phase but at 10.541u of phase. This error is much larger than my vtol value.

But when I chnaged to strobeperiod of tran analysis to  1ns, abstime shows up at phase value of 10.002u.

I wonder why such descrpancy and why vtol  is NOT playing any role here.

Kind Regards,

 

 

Parents
  • RFStuff

    Dear Andrew,

    Thanks a lot for your time and reply.

    I realised that it is NOT the cross() issue.

    The issue lies in idt(). 

    When the "phase" crosses "T_period" ( cross() is accurate no doubt ) , "reset" becomes one 1 at that instant.

    But idt() becomes zero in the next time point which is NOT controlled one ( it depends upon Spectre simulation).

    This leads to period error of the Oscillator.

    Same is the case for idtmod(). 

    Is there any way I can make idt() = 0 at the exact time instant when "reset" becomes 1 though it is completely abrupt and discontinuous.

     

    Kind Regards,

     

Reply
  • RFStuff

    Dear Andrew,

    Thanks a lot for your time and reply.

    I realised that it is NOT the cross() issue.

    The issue lies in idt(). 

    When the "phase" crosses "T_period" ( cross() is accurate no doubt ) , "reset" becomes one 1 at that instant.

    But idt() becomes zero in the next time point which is NOT controlled one ( it depends upon Spectre simulation).

    This leads to period error of the Oscillator.

    Same is the case for idtmod(). 

    Is there any way I can make idt() = 0 at the exact time instant when "reset" becomes 1 though it is completely abrupt and discontinuous.

     

    Kind Regards,

     

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