Design of a 4 GHz quadrature LC -VCO with transformer coupling

A 4 GHz quadrature voltage-controlled oscillator (QVCO) topology is proposed where a planar spiral transformer is used as coupling terminals. Two identical LC oscillators are cross-coupled by the transformer to generate the quadrature outputs. The transformer also serves as filtering network for the oscillators to improve the phase noise performance. The quadrature oscillator based on the proposed topology with additional design ideas has been implemented in a 0.18 um mixed-signal 1P6M CMOS technology for 4 GHz-band operation. The simulation gave a phase noise of -122dBc/Hz at 1 MHz offset with an output power of 1dBm, while dissipating 7.8 mA under a 1.8 V supply.