A 2.4 GHz Low Phase Noise In-Phase Coupled Class-C Quadrature VCO in 0.18 <formula formulatype="inline"><tex Notation="TeX">$\mu{\rm m}$</tex></formula> CMOS

Abstract

This letter presents a 2.4 GHz Class-C QVCO using an in-phase coupling topology. The phase noise of the proposed QVCO is effectively reduced by using a lower gate biasing voltage at the cross-coupled pairs and an in-phase coupling technique. A complementary Class-C oscillator is employed to enhance the startup robustness over a temperature range from $-25^{\circ}{\rm C}$ to 100 $^{\circ}{\rm C}$ . A quadrature oscillator, implemented in a 0.18 $\mu{\rm m}$ CMOS process, achieves a phase noise lower than $-$ 130.7 dBc/Hz at 1 MHz offsets and a frequency tuning range from 2.23 to 2.57 GHz while only consuming 3 mW. The design attains a remarkable figure-of-merit of 193.7 dBc/Hz.