Low-Voltage, Full-Swing Voltage-Controlled Oscillator With Symmetrical Even-Phase Outputs Based on Single-Ended Delay Cells

Implementing a symmetrical even-phase ring-type voltage-controlled oscillator (VCO) is difficult when using a full-swing single-ended delay cell; however, the full-swing characteristic of this architecture improves the signal-to-noise ratio. Conventional symmetrical even-phase output VCOs require tail current circuits to implement differential delay stages. Therefore, full-swing requirements make conventional symmetrical even-phase output VCOs impractical. This paper proposes a new CMOS VCO. In addition, it can achieve wide tuning range, full-swing, even-phase outputs, and less supply voltage using the proposed single-ended delay stage. Moreover, its simple topology features multiple output phases and linear frequencyvoltage characteristics. The proposed topology was validated in a four-stage VCO operated at 12.6-48 MHz, which yielded -109.38 dBc/Hz phase noise (at 1 MHz). Maximal power consumption approximated 1.2 mW in low-frequency mode and 1.8 mW in high-frequency mode at 1.2 V of the supply voltage in a Taiwan Semiconductor Manufacturing Company 0.18-μm RF CMOS process.