A fully integrated spiral-LC CMOS VCO set with prescaler for GSM and DCS-1800 systems

A set of two VCOs is developed in a 0.4 /spl mu/m CMOS process, using a fully integrated spiral inductor with symmetrical octagonal shape in the resonance LC-tank. One VCO operates at a 900 MHz center frequency, and the other at 1.8 GHz, both achieving the required phase noise spec and tuning range for the GSM and DCS-1800 system. The phase noise equals -108 dBc/Hz at 100 kHz offset for the 900 MHz version and -113 dBc/Hz at 200 kHz for the 1.8 GHz version. The power consumption is 9 and 11 mW. An eight-modulus prescaler operates together with both VCOs.