Very low noise current- shaped optimally coupled CMOS LC quadrature VCO

Abstract

This paper presents a new low phase noise quadrature voltage-controlled oscillator (QVCO). Coupling phase shifts of 90 • in conjunction with center-tapped capacitor impedance transformers are exploited to optimally couple two VCOs. DC and AC path of the switching and coupling pairs are de-coupled to allow operation in saturation for large oscillation amplitudes. The switching and coupling transistor pairs operate in class-C mode which increases the DC to RF efficiency. Also, these transistors alternate from strong inversion to accumulation region, decreasing the intrinsic device flicker noise. Simulations confirm the superiority of the proposed circuit in comparison with the prior published QVCOs in terms of phase noise performance.