A Distributed Dual-Band LC Oscillator Based on Mode Switching

In this paper, we present a distributed dual-band LC oscillator suitable for low-phase-noise applications. It switches between the odd and even resonant modes of a fourth-order LC resonator. In contrast to other switched-resonator designs, the switches used for mode selection do not carry current, and therefore, do not affect the quality factor of the resonator, which leads to low phase noise. Analysis shows it achieves the same phase-noise figure-of-merit (FoM) as a single-band LC oscillator that uses the same inductor and active core. This was verified by a prototype in a 0.13-μm CMOS process. It draws a current of 4 mA from a 0.5-V power supply and achieves a FoM of 194.5 dB at the 4.9-GHz band and 193.0 dB at the 6.6-GHz band, which is the same as the reference standalone LC oscillator. There is good agreement among theory, simulation, and measurement results.