Subharmonically injection-locked PLL with variable pulse-width injections

In this paper, we present a subharmonically injection-locked phase-locked loop (IL-PLL) with pulsed injection. When the pulsed injection signal is decomposed into its harmonics, we found that the oscillator responds only to the fundamental and harmonic elements of the oscillation frequency. The magnitude of these elements depends on the injection pulse width. Therefore, in order to increase the injection locking range, an adjustment of the injection pulse width is required. Compared with conventional pulsed injection, the bandwidth required by our pulse generator is reduced because the longer injection pulse width maintains the same injection-locking ability compared to the conventional injection pulse. We also investigate two specific injection methods, namely direct current injection and capacitive coupling injection, using theoretical analysis and circuit simulation. We design a test circuit of our proposed IL-PLL using a 0.18-μm standard CMOS process.