*2.1. System Design*

Figure 2 illustrates a proposed fully integrated AC-DC converter. A cross-coupled CMOS bridge circuit [7] is used in a full bridge rectifier (FBR). An additional diodeconnected NMOS (ND) is needed in order to not flow reverse current when the voltages at IN1 and IN2 become lower than the regulated output voltage VDD. An active diode [8] can be placed in parallel with N<sup>D</sup> to reduce the voltage drop. In this design, low power is prioritized. An active diode requires an opamp, which consumes power. Bandgap reference (BGR) operates with VDD, which is controlled by the output voltage VREF.

**Figure 2.** AC-DC converter for an ES-EH proposed in this work.
