2012 Volume 9 Issue 21 Pages 1624-1629
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×fref), 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 (fref) reference signal was input, output frequencies of 4.5×, 4.75×, and 5×fref 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×fref).