Ring oscillator having large load driving capability for use as VCO in phase locked loops

摘要

A VCO circuit 4 of a PLL circuit 1 includes M delay time variable inverters 5.1 to 5.M which are connected in a ring shape. Load driving capability of delay time variable inverters 5.1 to 5.M is increased gradually toward output node OUT which is connected directly to load capacity CL. Accordingly, a high load driving capability is obtained without provision of a separate buffer.