This paper reports an ultralow-voltage (ULV) energy-harvesting bluetooth low-energy (BLE) transmitter (TX). It features: 1) a fully integrated micropower manager ( μ PM) to customize the internal supply and bias voltages for both active and sleep modes; 2) a gate-to-source-coupling ULV voltage-controlled oscillator (VCO) using a high-ratio (5.6:1) stacking transformer to improve the phase noise and output swing; 3) an ULV class-E/F power amplifier (PA) with an inside-transformer LC notch to suppress the HD, and finally 4) an analog type-I phase-locked loop (PLL) with a reduced duty cycle of its master-slave sampling filter (MSSF) to suppress the jitter and reference spur. The TX prototyped in 28-nm CMOS occupies an active area of 0.53 mm and exhibits 25% system efficiency at 0-dBm output at a single 0.2-V supply. Without resorting from any external components, both the output HD-49.6 dBm) and HD-47.4 dBm) comply with the BLE standard. The FSK error is 2.84% and the frequency drift in a 425- μs data packet is <5 kHz under open-loop modulation. The use of negative-voltage power gating suppresses the sleep power of the entire TX to 5.2 nW.