5-6 GHz SiGe VCO with tunable polyphase output for analog image rejection and I/Q mismatch compensation

Image rejection and demodulation quality are adversely affected by in-phase and quadrature (I/Q) channel phase mismatch. This paper presents a 5-6 GHz Silicon Germanium (SiGe) voltage controlled oscillator (VCO) and integrated polyphase filter with I/Q phase imbalance compensation. The design of the VCO is discussed, including considerations for high inductor quality factor (Q) and low VCO phase noise. From a 2.5 V supply, the VCO core consumes 3 mA. The simulated phase noise at 1 MHz from the carrier is -114.6 dBc/Hz. The I/Q imbalance of the polyphase splitter is tunable by means of series output varactors. The polyphase network design can compensate for ±4° I/Q phase imbalance, which could provide approximately 15 dB improvement in image rejection in a Weaver architecture receiver.