A 2.4GHz fully integrated CMOS VCO with direct FM/FSK modulation capability

The design and implementation of a 2.4GHz fully Integrated VCO with direct FM/FSK modulation capability is presented. The VCO utilizes an accumulation mode MOS (aMOS) varactor as the major frequency tuning element. A tiny aMOS varactor of similar geometry is also incorporated in parallel for direct baseband modulation. Abrupt CV profile of aMOS varactor is linearized through direct coupling to the full-swing of the VCO tank circuit. Concept of this large-signal CV linearization Is fully elaborated. The VCO prototype has been fabricated in 0.35mum standard CMOS process. Measured at 3.0V supply, the VCO demonstrates 14% tuning range, 920KHz/V linear modulation gain, -103dBc/Hz phase noise at 100KHz offset frequency with core current drawn of approximately 7mA.