A New Low-Noise Dual-Band VCO for WLAN/WIMAX

In this paper, a new dual-band voltage-controlled oscillator (VCO) is proposed. The proposed VCO utilizes a fourth-order LC resonator that oscillates at two different frequencies. Moreover, its oscillation frequency can be chosen by switching the tail current between two different values. The switches are placed in a way that their resistances do not affect the quality factor of LC tanks, and phase noise does not increase. The proposed VCO is thoroughly analyzed by deriving a nonlinear model. The required conditions for oscillation and switching between two oscillation frequency bands are calculated approximately using averaging. Moreover, the VCO transient behavior in switching the oscillation frequency is investigated, and amplitudes of oscillation at two oscillation modes are calculated. The VCO is designed and simulated in $$0.18\,\upmu \hbox {m}$$0.18μm CMOS technology to verify the design and analytical equations and to evaluate the performance of the proposed VCO. In comparison with the literature, proposed simulations show acceptable phase noise and transient behavior. In addition, the accuracy of the analytical equations is also verified.

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