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Capactance value became negative in Charge solver

    • krishnanunnira.20

      While simulating a p-i-n modulator in forward biased condition using a DC+ small signal ac signal, the capacitance value obtained is negative after a certain DC voltage and it will remain negative till some 20GHz frequency. Since capacitance cannot be negative what can I do to rectify the issue.

      Capacitance value is calculated in the same way as that of a traveling wave modulator example in Lumerical.

      Also how can I obtain the total resistance of the device in this case.

    • Guilin Sun
      Ansys Employee

      negative capactance: by definition it is the difference of charges over voltage, delta_Q/delta_v. It is possible to have positive and negative numerically. Proper choice of delta_c might be important.


      you may refer this example for resistance

      as now you have voltage and current.


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