Low-Phase Noise LC-tank Quadrature Voltage Controlled Oscillator

A low phase noise LC-tank quadrature voltage controlled oscillator (QVCO) is described. Two differential pairs (one for negative g_m generation and the other one for the coupling input) of each resonator have separate bias current sources which are switched on and off by the coupling input of each resonator. The measured results of 5GHz quadrature VCOs (QVCO) implemented in a 0.13mum CMOS process shows the proposed biasing scheme can improve the phase noise by 17dB from the conventional QVCO with constant tail current sources while the two QVCOs consume the same power (4.4mA from a 1.2V supply). The smaller 1/f noise of the switched current source improves the phase noise by 7dB. The additional 10 dB improvement of the phase noise is obtained by employing the coupling input as the switching signal and separating the tail current sources for the two differential pairs of each resonator