A low-phase-noise 5GHz quadrature CMOS VCO using common-mode inductive coupling

A new concept for quadrature coupling of LC oscillators is introduced and demonstrated on a 5GHz CMOS VCO. It uses injection-locking through common-mode inductive coupling to enforce quadrature. The technique provides quadrature over a wide tuning range without introducing any phase noise- or power consumption increase. The realized VCO is tunable between 4.6GHz and 5.2GHz and measures a phase noise lower than -124dBc/Hz at 1MHz offset over the entire tuning range. The circuit draws 8.75mA from a 2.5V supply.