Abstract: A novel LC oscillator differentially tuned by switched step capacitors,which is implemented in a CMOS 0.25μm 1P4M CMOS process,is proposed to verify our theoretical analysis of tuning characteristics.The tuning capacitance of the proposed switched step capacitors is 146% of the conventional inversion-MOS varactors’.In the 1/f~3 region,the novel differentially tuned topology has 7dB phase noise reduction compared to the single-ended tuned topology.The implemented VCO at 1.013GHz has a phase noise of -83,-107, and -130dBc/Hz, at a 10kHz,100kHz, and 1MHz offset,respectively.Power consumption is 8.6mW.

Key words: step capacitors, MOS varactors, switched step capacitors, voltage-controlled oscillator, oscillator tuning curves, period calculation technique