This letter proposes a wide locking range injection locked frequency divider (ILFD) and describes the operation principle of the ILFD. The circuit is made of a dual band two-stage differential complementary metal-oxide-semiconductor (CMOS) ring oscillator and is based on MOS switches directly coupled to the differential outputs of the ring oscillator. The divide-by-two ILFD can provide wide locking range and the measurement results show that at the supply voltage of 1.8-V, the divider free-running frequencies are 1.36GHz and 2.3GHz, and at the incident power of 0dBm, the locking range is about 1.75GHz from the incident frequency 1.9GHz to 3.65GHz at low band and 2.55GHz from 2.95GHz to 5.5GHz at high band