Many of today's applications require that a phase-locked loop (PLL) operate at high speeds, while maintaining reasonable phase noise and jitter performance. Voltage-controlled oscillators (VCO) are important building blocks in PLLs. More importantly, the VCO is the major contributor of phase noise in a PLL. The noisy environment, mainly due to the switching noise generated by the digital portion of these systems. imposes stringent constraints on the design of VCOs, especially phase noise or timing jitter. The switching noise originated in the digital portion of the systems are coupled to the supply and ground rails of the VCO of PLLs. Another important block of a PLL is the charge-pump, a block that is responsible for generating the control voltage to be applied to the VCO. The stability or fluctuation of the control voltage, can severely affect the phase noise performance of the VCO. The research in this thesis, centered on (i) the design considerations of CMOS charge-pumps, (ii) the timing jitter of the delay-cells of low-voltage CMOS ring-VCOs and (iii) the design of a high-speed ring oscillator. A PLL was designed using a new active inductor 6.3-GHz ring oscillator, with a tuning range of +/- 15% was designed in 0.18um CMOS technology. The ring oscillator employed active inductor loads that resulted in an improvement of about 42% in oscillation frequency when compared to the conventional resistor loaded ring oscillator.
Low-Voltage High-Speed Ring Oscillator With a-InGaZnO TFTs
