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Help explain the capacitance definition in Spice

  1. Jan 27, 2014 #1
    In Spice, the capacitance between two points x, y is defined as follows:
    Cxy = - dQx / dVy for x != y
    Cxx = dQx/dVx

    Could anyone help me explain why it is defined like that?
    I know that C = dQ/dV but the formula above seems strange to me.

    Is my understanding below correct?
    Cxy = dQx/d(Vx - Vy)
  2. jcsd
  3. Jan 27, 2014 #2


    User Avatar

    Staff: Mentor

    Could you say more about where you are seeing this in SPICE? Which version of SPICE?

    I'll check my SPICE Model Definition Textbook tomorrow at work, but that doesn't ring any bells at the moment. It looks more like an ANSYS or other physical simulator model...?
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