Ring Oscillator Based Injection Locked Frequency Divider Using Dual Injection Paths

Ring oscillator based injection locked frequency dividers (ILFD) generally feature higher power efficiency compared to conventional static frequency dividers. However it is difficult for ring oscillator based ILFDs to achieve large division ratio and wide input locking range at the same time. To increase the input locking range, a ring oscillator based ILFD utilizing dual injection technique is proposed in this letter. For this, both tail injection and direct injection are applied in phase such that the output currents of the two mixing processes corresponding to the two injection paths are added constructively at the output frequency ωo and the overall injection efficiency is therefore increased. A differential buffer circuit with dual injection is proposed. Equivalent circuit modeling of the dual injection buffer and mathematical analysis of locking range enhancement are presented. The core ring oscillator consists of 4 stages of the dual injection buffers. It is fabricated in a 65 nm CMOS technology and consumes less than 2 mW with supply voltage of 1.2 V. Its locking range is from 1.2 to 20.7 GHz without any tuning at 0 dBm injection power level. The proposed ILFD is compact with the core only occupying 15 μm × 30 μm and does not need any extra controls, making it suitable for integrated wideband phase locked loop.