Energy harvesting (EH) is a topic of intensive research promising battery-free operation of massive networks of wireless IoT devices. To simultaneously satisfy the EH and IoT, ultra-low-power (ULP) consumption with ultra-low-voltage (ULV) supply are required. Some, e.g., photovoltaic, EH output voltage (<0.3V) is below the threshold voltage (V_t) of even the most recent FinFET CMOS transistors, which makes it extremely challenging for circuit designers. Thus, new special circuit techniques are needed to make the IoT devices work properly with supplies below V_t.