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

The design and implementation of a 2.4 GHz 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 0.35 μm standard CMOS process. Measured at 3.0 V supply, the VCO demonstrates 14% tuning range, 920 KHz/V linear modulation gain, -103 dBc/Hz phase noise at 100 KHz offset frequency with core current drawn of approximately 7 mA.