OVERLAPPING, TWO-SEGMENT CAPACITOR BANK FOR VCO FREQUENCY TUNING

摘要

A VCO (for example, in an FM receiver) includes an LC resonant tank. The LC resonant tank includes a coarse tuning capacitor bank and a fine tuning capacitor bank. The coarse tuning capacitor bank contains a plurality of digitally controlled coarse tuning capacitor elements, each providing a first capacitance value when active. The fine tuning capacitor bank contains a plurality of digitally controlled fine tuning capacitor elements, each providing a second capacitance value when active. To address the practical problem of capacitor mismatch, capacitance overlap throughout the VCO tuning range is created by selecting the first and second capacitance values such that the capacitance value of the fine capacitor bank is greater than the first capacitance value when all of the digitally controlled fine tuning capacitor elements of the fine capacitor bank are active.