Ultra-low-phase-noise CMOS LC quadrature voltage controlled oscillator with Colpitts topology

A new low-phase-noise colpitts LC quadrature voltage controlled oscillator (QVCO) is presented. The proposed QVCO is realised by coupling two differential current-switching Colpitts oscillators in an `in-phase-anti-phase´ manner. The coupling technique between the two Colpitts LC-voltage controlled oscillators (VCOs) has significantly improved the phase noise of the proposed circuit without using any extra elements. The oscillation frequency of the proposed LC-QVCO is 4 GHz. The Colpitts QVCO exhibits a phase noise of -131.5 and -141.3 dBc/Hz at 1 and 3 MHz offset, respectively. By generalising the coupling scheme to more than two differential Colpitts VCOs in a loop, multiphase signals can be generated.