Hi!

I am trying to simulate a design with DFFs using AMS in ADE. The design components are picked form the standard cell library that we are using. The problem I am facing is that when I perform an electrical simulation on the design everything works fine as desired but when I switch to the functional view of the blocks the circuit output is X. I tried to debug this issue and it comes to the fact the outputs of DFFs in the design are always at X. I am resetting the DFFs initially before the circuit starts operating but still no success.

My question is there a special way to setup simulations of design involving DFFs or is there something wrong with my setup.

Hi!

Yes I am using the analog stimuli as for the connect modules are concerned I just modified them so that the Vsupp=1.2 instead of 1.8 as default and have faster tr and tf=10ps (instead of 0.2ns) . Apart from that    if the simulation works for my own code of a DFF it should work for the other one too (so I am guessing that the connect modules are OK). As for the functional description is concerned its very very messy as it has descriptions of all the standard cells(that we got from our vendor) I am looking in to it but its very helpful I must say.

So I just thought maybe someone else saw the same issue.  :-?

Yes I am using 1.2V supply with 10ps rise and fall times. Yes I think the stimuli should meet the requirements as I have specified it to be so. Here is a code for the DFF I am talking about and I don't see any issue why it shouldn't work

`define DFF_CP_R_Q_R 0.1
`define DFF_CP_R_Q_F 0.1
`define DFF_D_CP_HOLD_posedge_posedge 0.01
`define DFF_D_CP_HOLD_negedge_posedge 0.01
`define DFF_D_CP_SETUP_posedge_posedge 0.01
`define DFF_D_CP_SETUP_negedge_posedge 0.01
`define DFF_CP_PWL 0.01
`define DFF_CP_PWH 0.01

module DFF (Q, D, CP);

     output Q;
     input D;
     input CP;

`ifdef functional
     reg  NOTIFIER;
     GP_U_FD_P_NOTI   U1 (IQ, D, CP , NOTIFIER) ;
     buf   #1 U2 (Q, IQ) ;

`else
     reg  NOTIFIER;
     GP_U_FD_P_NOTI   U1 (IQ, dD, dCP , NOTIFIER) ;
     buf   #1 U2 (Q, IQ) ;


     specify

            (posedge CP => (Q +: D)) = (`DFF_CP_R_Q_R,`DFF_CP_R_Q_F);

           $setuphold(posedge CP, posedge D, `DFF_D_CP_SETUP_posedge_posedge, `DFF_D_CP_HOLD_posedge_posedge , NOTIFIER,, , dCP, dD);
           $setuphold(posedge CP, negedge D, `DFF_D_CP_SETUP_negedge_posedge, `DFF_D_CP_HOLD_negedge_posedge , NOTIFIER,, , dCP, dD);
           $width(negedge CP, `DFF_CP_PWL ,0, NOTIFIER);
           $width(posedge CP, `DFF_CP_PWH ,0, NOTIFIER);

     endspecify

`endif

endmodule // DFF

`endcelldefine
`celldefine
`ifdef functional
  `timescale 1ns / 1ns
  `delay_mode_unit
`else
  `timescale 1ns / 1ps
  `delay_mode_path
`endif

Could you please suggest with these delay settings what should the values of tr and tf for the connect files be?

Also I would like to mention that
Vthi 0.666
Vtlo 0.333
Tr0.2n

Many thanks for the reply BOE i'm much obliged. Sorry about the hiccup I copied theses parameters from the original file and not the modified one. (0.2n was the original Tr).

The stimuli are currently vpulse as clk(operating@ 1G) and same as reset for initial 100ns and a vdc for data.

Sorry for my ignorance but how did you come up with 100MHz for 1ns. Since the time scale defined in the model file is 1ns/1ns, Should I modify the model file and redefine the the time scale to something more appropriate like 1p (that would be like 100GHz if I am right from your above suggestion 1/10 of time step).

Yeps got that. Just for the sake of checking a designs functionality how can I turn of these timing checks using -notimingcheck if I use ADE to perform ams simulations?