A 2.4-GHz subharmonically injection-locked PLL (SILPLL) with injection timing calibration is realized. The injection timing issues has been clearly described and modeled mathematically. An injection timing calibration technique is presented to ensure the best phase noise performance. This work is fabricated in 0.18-μm process with 12.6-mW power consumption. The measured phase noises at 1 MHz offset before and after injection are -114 and -129 dBc/Hz, respectively. The measured rms jitter integrated from 1 kHz to 40 MHz before and after injection are 317 and 145 fs, respectively.