A technique for truly linear LC VCO tuning, a proof of concept

Based on the understanding of the relation between the shape of the LC VCO tuning curve and the varactor characteristics, a technique using an array of unequal varactors with different bias was found to obtain a truly linear tuning curve. An LC VCO was designed using TSMC 0.13 μm 1.2 V/3.3 V IO process, the VCO frequency varies from 1.9 to 2.7 ghz as its control voltage varies from 0 to 1.2 V. The tuning gain was KVCO=630 MHz/V ±9.5%.