Patent ID: 7026880

Claim:
A quadrature voltage control oscillator (VCO), comprising: a current source, controlled by a first voltage level, for providing a constant current; a capacitor, coupled to the current source in parallel between a voltage supply and a first node; a first tank circuit, having a first inductor and a first varactor coupled in parallel between a second node and a third node, controlled by a second voltage level; a second tank circuit, having a second inductor and a second varactor coupled in parallel between a fourth node and a fifth node, controlled by the second voltage level; a first differential pair, coupled between the current source and the first tank circuit, wherein the first differential pair is coupled to the current source in series via the first node and is coupled to the first tank circuit in parallel via the second node and the third node; a second differential pair, coupled between the current source and the second tank circuit, wherein the second differential pair is coupled to the current source in series via the first node is coupled to the second tank circuit in parallel via the fourth node and the fifth node; a first ring oscillator, coupled to the first tank circuit in parallel via the second node and the third node, and coupled between the first differential pair and a ground voltage level in series; a second ring oscillator, coupled to the second tank circuit in parallel via the fourth node and the fifth node, and coupled between the second differential pair and the ground voltage level in series; a first source follower, associated with the second node; a second source follower, associated with the third node; a fourth source follower, associated with the fourth node; and a fourth source follower, associated with the fifth node, wherein a positive first output voltage of the first source follower and a negative first output voltage of the second source follower form a first output voltage level, and a positive second output voltage of the third source follower and a negative second output voltage of the fourth source follower form a second output voltage level differed from the first output voltage level by quadrature phase.