Design and optimization of a linear wide-band VCO for multimode applications

An LC VCO designed in a 0.25 μm BiCMOS-SiGe process achieves a tuning range of 2.8-3.75 GHz while drawing 1.3 mA from a 2.5 V supply. The proposed circuit design techniques for both passive and active parts of the VCO enable an optimum trade-off to be achieved among tuning range, phase noise, power consumption and sensitivity to substrate and supply noise. Two self-calibrations methods are proposed, analyzed and their circuits are integrated to compare their measured performances. This comparative study shows that, for the same low VCO gain, the number of switched-capacitor units can be reduced from 15 (4 bits) in the conventional calibration approach to 1 in the proposed linearization based approach. Consequently, the digital calibration circuit is significantly simplified (only one comparator) and the settling time of the digital calibration is greatly reduced.