Abstract: This paper introduces a 2.5GHz low phase-noise cross-coupled LC-VCO realized in 0.35μm SiGe BiCMOS technology.The conventional definition of a VCO operating regime is revised from a new perspective.Analysis shows the importance of inductance and bias current selection for oscillator phase noise optimization.Differences between CMOS and BJT VCO design strategy are then analyzed and the conclusions are summarized.In this implementation,bonding wires form the resonator to improve the phase noise performance.The VCO is then integrated with other components to form a PLL frequency synthesizer with a loop bandwidth of 30kHz.Measurement shows a phase noise of -95dBc/Hz at 100kHz offset and -116dBc/Hz at 1MHz offset from a 2.5GHz carrier.At a supply voltage of 3V,the VCO core consumes 8mA.To our knowledge,this is the first differential cross-coupled VCO in SiGe BiCMOS technology in China.

Key words: SiGe BiCMOS, VCO, inductance, phase noise