*4.2. Limination of the Proposed Converter on V<sup>A</sup> and R<sup>S</sup> of ES-EH*

To see which electrical parameters of ES-EH allowed the converter to output a regulated voltage of 1 V, SPICE simulation was performed with various amplitude voltages V<sup>A</sup> and output resistances R<sup>S</sup> of ES-EH under the condition of a load resistance of 1 MΩ, as shown in Figure 11. The middle area in blue shows that VDD is regulated between 0.95 V and 1.0 V. ES-EH with too high Rs inputs insufficient power into the regulator against the output power, whereas ES-EH with too low Rs injects too much power so that the PD path cannot pull down to the target regulation point. The lower bound on Rs can be reduced with a larger PD size. Ω

**Figure 11.** Simulated VDD with different V<sup>A</sup> and R<sup>S</sup> under a load resistance of 1 MΩ Ω in (**a**) 3D and (**b**) top view plots.
