Figure 3.

Example of the oscillation waveforms of $v_{12}\left(t\right)$ and $v1\left(t\right)$ measured in the circuit of Figure 2b. The $R_{\mathrm{X}}$ and $C_{\mathrm{X}}$ were set to 4.0 kΩ and 10 nF, respectively. The segment of time with a colored background corresponds to two cycles of the oscillation and was used for the subsequent discrete Fourier transform (DFT) analysis.