Evaluation of Digital Crosstalk Noise on Differential Input Voltage Controlled Oscillator

With an increase in the operation frequency of complimentary metal oxide semiconductor (CMOS) circuits, a radio-frequency system-on-a-chip (RF-SOC) that integrates GHz-RF and large-scale digital circuits becomes a key device for wireless systems and high-speed networks. To develop high-performance RF-SOCs, high quality voltage controlled oscillators (VCOs) are required as local oscillators or clock generators, which operate in noisy environments suffering from crosstalk noise generated by digital circuits. A 0.25 µm CMOS test chip for a new differential-input VCO and a conventional single-input VCO was designed with on-chip CMOS logic noise sources and substrate noise detectors. The jitter and phase noise of the VCOs were measured to investigate the effect of substrate crosstalk noise. We confirmed that the differential-input VCO is robust to low-frequency noise in comparison with a conventional single-input VCO.