Design of a CMOS multi-mode GNSS receiver VCO

A voltage-controlled oscillator (VCO) with dual stages of accumulation mode varactors for a multi-mode global navigation satellite system (GNSS) application, which adopts sigma-delta fractional-N technology in the synthesizer, is presented. The structure is selected to optimize the frequency coverage and tuning linearity, based on a general analysis of the parasitic capacitance in the coarse tuning switch bank cells, which cover the global positioning system (GPS) and Beidou (BD) bands. The VCO implemented in the 0.18 μm CMOS process can cover the GPS L1, BD B1, B2 and B3 bands with sufficient margin, and exhibits low phase noise by using this tuning curve linearization technique. The equalized K _vco characteristic behavior further offers a wide voltage tuning range and improves the stability of the closed loop.