Patent ID: 7830212

Claim:
A phase locked loop, comprising: a phase-frequency detector (PFD), receiving a reference signal and a feedback signal to determine phase and frequency errors; a loop filter, coupled to the phase-frequency detector, filtering the phase and frequency errors to generate a control voltage; a voltage controlled oscillator (VCO), coupled to the loop filter, generating a VCO output signal according to the control voltage, comprising: a transmission line pair, having a length, short-circuited at one end pair and open-circuited at the other end pair, providing the VCO output signal with an initial VCO wavelength; a cross-coupled transistor pair, directly connected to one third of the length of the transmission line pair from the short circuited end pair; and a varactor, coupled to the open-circuited ends of the transmission line pair, adjusting the initial VCO wavelength of the VCO output signal according to a control voltage to a final VCO wavelength, wherein the length of the transmission line pair is three quarter of the initial VCO wavelength; and a 3-stage frequency divider, coupled to the voltage controlled oscillator, dividing the frequency of the VCO output signal 3 times to generate the feedback signal.