Patent ID: 7106142

Claim:
A ring-type voltage-controlled oscillator comprising a plurality of delay cell circuits, wherein each delay cell circuit has at least an output coupled to an input of a next sequential delay cell circuit in the ring-type voltage-controlled oscillator and one of the delay cell circuits comprises: a first inverter comprising a first NMOS transistor having a gate receiving a first differential input signal, a drain generating a first differential signal and a source coupled to a second power rail and a first PMOS transistor having a drain coupled to the drain of the first NMOS transistor, and a source coupled to a first power rail; a second inverter comprising a second NMOS transistor having a gate receiving a second differential input signal and a drain generating a second differential signal and a source coupled to the second power rail; a first resistance unit coupled to the drain of the first NMOS transistor, receiving the first differential signal; a second resistance unit coupled to the drain of the second NMOS transistor, receiving the second differential signal; and a differential delay circuit coupled to the first power rail for generating a first differential output signal to a first terminal and the first resistance unit, and a second differential output signal to a second terminal and the second resistance unit; wherein the first and second resistance units have a resistance value adjusted according to a resistance control voltage for controlling the strength of the first and second NMOS transistors so as to alter the time delay of the first and second differential output signals.