The paper presents a novel Class-C type QVCO using a capacitive source coupling mechanism to enhance the startup robustness over process-temperature- voltage variations. Class-C type oscillator has superior phase noise performance with low power consumption at the cost of weak startup. In this design, complementary architecture and capacitive source degeneration coupling are employed to increase the loop gain of Class-C quadrature oscillator. The capacitive coupling mechanism also provides extra phase shifts that eliminate the quality factor degradation of the LC tank in QVCO design. An optimal coupling factor is derived to compromise power-phase noise trade-offs. The proposed 2.4GHz QVCO, fabricated in 0.18μm CMOS technology, achieves -128dBc/Hz at 1MHz offsets while only consuming 2.6mW. The design attains a remarkable figure-of-merit (FOM) of -192dB/Hz.