Massive deployment of wireless sensor tags (e.g. iBeacon) will only happen if batteries and their replacement effort are avoided. Self-powering by harvesting the ambient energies like indoor solar and thermal gradient is prospective [1], but their inconstant sub-0.5V output hinders their utility. Adding boost converters and regulators inevitably worsens the system efficiency and integration level. This paper reports an energy-harvesting Bluetooth Low-Energy (BLE) transmitter (TX) (Fig. 28.5.1). It features a fully integrated micropower manager (μPM) to limit the sleep power and tolerate variation of the energy-source voltage (VDD, EH) down to 0.2V. U=An ultra-low-voltage (ULV) VCO and Pa, and a passive-intensive type-I PLL are proposed. Fabricated in 28nm CMOS, the TX exhibits a 25% system efficiency at 0dBm output (Pout).