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 /spl mu/m 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.