Reduction of 1/f³ phase noise in LC oscillator with improved self-switched biasing

According to the discussion of noise sources and up-conversion mechanisms of flicker noise, an LC oscillator with improved self-switched biasing and decoupling capacitor is presented. To minimize the 1/f³ phase noise, both source noise and conversion gain of flicker noise are desirable to reduce, rather than only one way in previous works. Flicker noise from tail-biasing transistors is reduced by self-switched biasing technology, and the up-conversion of flicker noise from cross-coupled pair is suppressed by decoupling capacitor at the same time. Phase noise and key parameters influencing phase noise are analyzed in detail. To guide the design, simple way to get optimum values of key parameters is also presented. This oscillator can work at low supply voltage to reduce power consumption considerably compared to conventional self-switched biasing. The proposed oscillator is fabricated in 0.18 μm CMOS process, and exhibits a low phase noise of −77.5 dBc/Hz (FoM = 181) and −122.8 dBc/Hz (FoM = 186) at 10 kHz and 1 MHz offset, respectively, from oscillation frequency of 2.55 GHz while dissipating 2.7 mA with 1.2 V supply voltage.