This paper demonstrates a compact BLE transmitter (TX) achieving fully on-chip integration and high system-efficiency. This BLE TX is constructed based on a 1.2 GHz 8-phases current-reused ring oscillator (RO) with a digital phase-locked loop (PLL). To mitigate the spurious emission, including HD2 caused by phase mismatches, an edge-timing calibration is proposed by reusing the digital PLL in this paper. A transformer-based Class-D PA with implicit LC-notch is implemented to improve the system efficiency with higher harmonic suppression for both HD2 and HD3 with a compact on-chip area. The presented TX supports both 1 Mbps and 2 Mbps GFSK modulation with low power consumption.