A variable capacitor is provided. The variable capacitor includes a plurality of capacitor segments. The plurality of capacitor segments are connected in parallel within the variable capacitor. When a plurality of candidate capacitances allowable to the variable capacitor according to a connection state of the plurality of capacitor segments connected in parallel are sorted in a magnitude sequence, the plurality of candidate capacitances form a geometric series. The variable capacitor is used for a Voltage Controlled Oscillator (VCO), and the VCO is used for a Phase Locked Loop (PLL).