An energy efficient digital polar transmitter (TX) based on 1.5bit Delta-Sigma modulator (DSM) and fractional-N injection-locked phase-locked loop (IL-PLL) is proposed. In the proposed TX, redundant charge and discharge of turnedoff capacitors in the conventional switched-capacitor power amplifiers (SCPAs) are avoided, which drastically improves the efficiency at power back-off. In the PLL, spur-mitigation technique is proposed to reduce the frequency mismatch between the oscillator and the reference. The transmitter, implemented in 65nm CMOS, achieves a PAE of 29% at an EVM of -25.1dB, and a system efficiency of 23.8%.