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readforce does not work in DC simulation

Qilong

Hi all, 

    Recently I am trying to play with the readforce in DC simulation. My test circuit is a series RC network (R=1 Ohm, C=1pf both from analogLib), with the two terminals connected to gnd. No sources are used. Then I specified the voltage value on the floating plate of the capacitor in a file (with only one line in it: net_flaoting 1). Then I use readforce to read this file in DC simulation, with any other parameters like force, readns empty.  

    From the descriptions in the spectre simulator user guide and the reference, I am expecting a voltage of 0.5V on the floating plate of the cap after the DC run (I used rforce=1 Ohm). However only 0V is shown. On the other hand, if I specified initial state in the cap and use force=dev, the desired 0.5V will be calculated. Comparing this two cases, could I ask why the simulator does not use the statement I wrote in the file? 

    PS: As a crosscheck, I used the same file in a transient simulation with the same network by setting readic=filename.  Then I can see the initial state is calculated quite well. The floating node starts to settle down from the initial voltage of 0.5V (again rforece=1 Ohm), which seems the file is recognisable by spectre.   

Parents
  • Hi Andrew,

    Here I have another question related to the priority of ic, skipdc, readic,readns in the transient options. My questions starts from the check of Parameter "icpriority" explained in the user guide and the reference.

    I used the same circuit as before. And I assigned the initial state of the capacitor in two ways at the same time, one by specifying ic in the device CDF, the other by assigning node voltage with readic="file.in". Meanwhile I leave other transient parameters empty (ic=all by default, skipdc and readns empty). Then I found the value in "file.in" was used and the CDF parameter was ignored. However, in the reference it says the icpriority is set to "netlist" by default in Spectre 15.1, which means the value in the ic statement in the netlist (CDF ic) should override that in the readic file. So there seems a contradiction, doesn't it?

    Another experiment I did is to check what "icpriority" means. I built two identical RC circuit, and assigned the two capacitors' initial values in two ways as above, but separately. Again leaving other transient parameters empty, I found both initial conditions are used correctly. But it seems to be contradictory with the statement of "icpriority" in the user guide(under Subsection "setting ic priority oreder"):

    "By default, if you specify an initial condition file with the readic parameter, initial conditions from the file are used, and the ic statements specified in the netlist are ignored. "

    Combining with the two effects shown above, does it mean that the overriding mechanism only function when there are contradictory ic statements at the same node, between netlist and readic? Or does ic=all by default change the priority internally?

    Furthermore, is there any priority table that can used to check the order of use between ic, skipdc, readic and readns?

    Sorry for my tedious questions. After using spectre for some time, I really want to make clear about every option instead of leaving them empty blindly. Many thanks ahead.


    Best regards,
    Qilong
Reply
  • Hi Andrew,

    Here I have another question related to the priority of ic, skipdc, readic,readns in the transient options. My questions starts from the check of Parameter "icpriority" explained in the user guide and the reference.

    I used the same circuit as before. And I assigned the initial state of the capacitor in two ways at the same time, one by specifying ic in the device CDF, the other by assigning node voltage with readic="file.in". Meanwhile I leave other transient parameters empty (ic=all by default, skipdc and readns empty). Then I found the value in "file.in" was used and the CDF parameter was ignored. However, in the reference it says the icpriority is set to "netlist" by default in Spectre 15.1, which means the value in the ic statement in the netlist (CDF ic) should override that in the readic file. So there seems a contradiction, doesn't it?

    Another experiment I did is to check what "icpriority" means. I built two identical RC circuit, and assigned the two capacitors' initial values in two ways as above, but separately. Again leaving other transient parameters empty, I found both initial conditions are used correctly. But it seems to be contradictory with the statement of "icpriority" in the user guide(under Subsection "setting ic priority oreder"):

    "By default, if you specify an initial condition file with the readic parameter, initial conditions from the file are used, and the ic statements specified in the netlist are ignored. "

    Combining with the two effects shown above, does it mean that the overriding mechanism only function when there are contradictory ic statements at the same node, between netlist and readic? Or does ic=all by default change the priority internally?

    Furthermore, is there any priority table that can used to check the order of use between ic, skipdc, readic and readns?

    Sorry for my tedious questions. After using spectre for some time, I really want to make clear about every option instead of leaving them empty blindly. Many thanks ahead.


    Best regards,
    Qilong
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