Centering simulation model based on actual versus nominal capacitance value

Depending on the tolerance of a capacitor, the actual measured capacitance value of that component may be different than the nominal or manufacturer-stated value. The assumed nominal capacitance value of samples used for modeling can have an effect on the model accuracy. Presented here are modeling differences seen when centering the model using the actual measured versus nominal capacitance. As an example, a KEMET CBR04 capacitor family model was developed using both nominal-based capacitance and actual-based capacitance on all substrates used for modeling. The S-parameter differences between the two methods are seen primarily for lower capacitance values, below 10pF, but can affect higher values as well, especially when using loose tolerance parts. The comparison of the actual and nominal-based models shows actual capacitance-based models providing improved accuracy and improved design centering in yield simulations for these cases.