Patent ID: 7710207

Claim:
A voltage controlled oscillator for providing an oscillating signal according to a control voltage, the voltage controlled oscillator comprising: a converting circuit supplied between a bias voltage and a ground voltage for converting the control voltage into a control current, wherein the converting circuit comprises: a first source degenerating device, wherein the control voltage is applied to the first source degenerating device for generating a first conducting current; a second source degenerating device, wherein a constant voltage is provided to the second source degenerating device for generating a second conducting current; a first current mirror coupled between the first source degenerating device and the second source degenerating device for generating a third conducting current; and a first current source coupled to the second source degenerating device, the first current mirror and the ground voltage for providing a first reference current; a replica bias circuit coupled to the converting circuit for providing a swing voltage; and a ring oscillating circuit coupled to the replica bias circuit comprising at least two delay units coupled in series for successively delaying an input signal as the oscillating signal after a period of delay time, wherein each delay unit has two differential input ends and two differential output ends; wherein the replica bias circuit adjusts a supply voltage applied to the ring oscillating circuit to determine the period of delay time according to the control current and the swing voltage.