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How sources and components are treated in DC analysis?

BaaB

Hi,

In DC analysis, capacitor is open and inductor is short. I would like to know what other things the DC analysis do (for example, how sources are treated,...). Could you tell me where can I find this? 

I tried search cdnshelp but the info is not there. It is an introduction about DC analysis.

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  • Andrew Beckett

    I'm not really sure why the analogLib components are confusing. Part of the reason they exist is for other simulators and for historical reasons. With spectre you can just always use the analogLib vsource, isource, and port components - these have a parameter which defines the type of the source and fields which change dynamically.

    The dc offset (which corresponds to the offset parameter on the source) is not affecting the DC operating point. It just adds that offset to all the points defined in the PWL vector during the transient.

    For any time-varying source, the time-zero value is whatever value that time-varying waveform would have had at time=0s. So if you have a sine source with a sinephase of 90 degrees, it will be the value that the sine wave has at a phase of 90 degrees (since that's the initial phase of the sine wave). 

    With a real example, if you do:

    v1 (n1 0) vsource type=pwl dc=1 offset=0.2 wave=[0 0.3 1m 0.7 2m -0.4]

    Then n1 will be 1V for the DC analysis. If you do:

    v1 (n1 0) vsource type=pwl offset=0.2 wave=[0 0.3 1m 0.7 2m -0.4]

    Then n1 will be 0.5V for the DC analysis (because the value at t=0s would be 0.3+0.2).

    Regards,

    Andrew.

Reply
  • Andrew Beckett

    I'm not really sure why the analogLib components are confusing. Part of the reason they exist is for other simulators and for historical reasons. With spectre you can just always use the analogLib vsource, isource, and port components - these have a parameter which defines the type of the source and fields which change dynamically.

    The dc offset (which corresponds to the offset parameter on the source) is not affecting the DC operating point. It just adds that offset to all the points defined in the PWL vector during the transient.

    For any time-varying source, the time-zero value is whatever value that time-varying waveform would have had at time=0s. So if you have a sine source with a sinephase of 90 degrees, it will be the value that the sine wave has at a phase of 90 degrees (since that's the initial phase of the sine wave). 

    With a real example, if you do:

    v1 (n1 0) vsource type=pwl dc=1 offset=0.2 wave=[0 0.3 1m 0.7 2m -0.4]

    Then n1 will be 1V for the DC analysis. If you do:

    v1 (n1 0) vsource type=pwl offset=0.2 wave=[0 0.3 1m 0.7 2m -0.4]

    Then n1 will be 0.5V for the DC analysis (because the value at t=0s would be 0.3+0.2).

    Regards,

    Andrew.

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