\draw[anchor=south] (0,0.00) ellipse (1.5cm and 0.75cm);
\draw[anchor=south] (0,0.25) ellipse (2.0cm and 1.00cm);
\draw[anchor=south] (0,0.50) ellipse (2.5cm and 1.25cm);

\node[align=center, text width=1.5cm] at (0,0.00) {intrinsic model};
\node[align=center, text width=1.5cm] at (0,1.00) {model};
\node[align=center, text width=1.5cm] at (0,1.50) {subcircuit};