RF CMOS differential oscillator with source damping resistors

This paper proposes a new method to suppress the 1/f noise contribution of active devices in an oscillator using source damping resistors. The operational mechanism of the proposed method is analyzed through circuit simulation with a complementary LC differential oscillator topology. This shows that the amount of 1/f noise and the mismatch of instantaneous current swing of the oscillator active devices can be substantially reduced with source damping resistors. The reduced 1/f noise and instant current mismatch leads to a phase noise improvement by suppressing 1/f noise up-conversion to phase noise. To prove experimentally the usability of the proposed technique, two complementary LC differential VCOs with different damping conditions are fabricated using 0.18 μm CMOS technology. The measurement result shows that there is about 6.0 dBc, 4.0 dBc and 1.0 dBc of phase noise improvement at 10 kHz, 100 kHz and 1 MHz offset frequency with source damping resistors, respectively.