Low-phase-noise wide-frequency-range differential ring-VCO with non-integral subharmonic locking in 0.18 µm CMOS

A low-phase-noise ring voltage-controlled oscillator (VCO) with subharmonic injection locking is presented. The ring VCO topology is designed to obtain not only an acceptable spurious level but also satisfactory phase-noise characteristics by enabling the use of short-pulse-width injection signals (83.3 ps). We also present the measurement results in the case of non-integral subharmonic locking such as quarter-integral subharmonic locking and half-integral subharmonic locking. The proposed VCO has a wide frequency tuning range, namely, 0.62-1.5 GHz. This range is realized by combining pMOS resistive loads and a circuit for shifting the bias level. Thus, rail-to-rail voltages can be used for control. The 1-MHz-offset phase noise of the VCO is -126 dBc/Hz at an output frequency of 1.35 GHz (= 13.5×100 MHz) and a spurious level of -48 dBc. At a spurious level of -40 dBc, the phase noise of the VCO at the same frequency (= 6.75×200 MHz) is -126 dBc/Hz. At a VCO output frequency of 1.35 GHz, the power consumption from a 1.8 V power supply is 41 mW. The VCO was fabricated by 0.18 μm CMOS technology and occupies an area of 0.014 mm².