Model for Realistic Capacitor

The left shows an RC circuit with ideal components which are typical in simulations. The right shows the same RC circuit with a modeled capacitor based on characteristics for a 1uF MLCC I found from TDK. The blue node is the input signal, the green node is the expected output with ideal components, and the orange node is the more realistic output with a non-ideal capacitor. In the frequency domain the left circuit acts perfectly: as frequency rises the capacitor’s impedance continues to decrease according to Xc=(1/ωC). The right circuit however reaches a lower limit for impedance then reverses this trend and impedance begins to rise with frequency. This is because of the parasitic components in the circuit; the additional resistors and inductor on the right side. These parasitic components are Insulation Resistance (Rins=0.5GΩ), Equivalent Series Inductance (ESL=0.37nH), and Equivalent Series Resistance (ESR=8.4mΩ). Impedance of a real capacitor will be lowest at the Self Resonant Frequency (SRF=8.3MHz) when the inductance and capacitance cancel. Before that point impedance decreases as frequency increases like a capacitor as expected, after that point it increases like an inductor because of the ESL, and exactly at the SRF impedance is determined by the ESR.

published 5 years ago