Injection-locked fractional frequency multiplier with automatic reference pulse-selection technique

Abstract

An injection-locked fractional frequency multiplier (ILFFM) based on a ring VCO is proposed. The ILFFM can output signals whose output-frequency step equal quarter of an input reference frequency (1/4×f_ref), with low-phase-noise characteristics due to injection locking. To realize this fractional frequency multiplication, an injection pulse selection circuit is demonstrated, which can select the appropriate injection pulse trains as to the VCO output phases. The proposed circuit was fabricated in 65nm CMOS process. When a 528-MHz (f_ref) reference signal was input, output frequencies of 4.5×, 4.75×, and 5×f_ref were obtained with low phase noise. A 1-MHz-offset phase noise with injection was -113dBc/Hz at the output frequency of 2.51GHz (=4.75×f_ref).