A Low Phase-Noise 9-GHz CMOS Quadrature-VCO using Novel Source-Follower Coupling Technique

A 9-GHz quadrature voltage-controlled oscillator (QVCO) with an improvement of 1/f noise performance due to the use of proposed source-follower coupling technique is presented. In contrast to conventional parallel or series coupling methods by which the coupling transistors are operated in saturation region, the source-follower coupling technique, which uses a coupling transistor operated in cut-off region, is invented. Therefore, 1/f noise is much lower than that of the conventional topologies due to the less turn-on duty cycle of the coupling-transistor than that of conventional one, which in turns results in smaller phase noise. It is found experimentally that the phase noise of the QVCO can be reduced by more than 8 dB due to the suppression the 1/f noise of coupling transistor by changing its operation condition from saturation to cut-off region. This QVCO achieves a phase noise of -115 dBc/Hz at 1-MHz-offset away from the 9.17 GHz carrier, corresponding to a figure-of-merit (FOM) of -183.4 dBc/Hz.