Integrated MOS Varicap, and Voltage Controlled Oscillator and Filter Having Same

An integrated MOS varicap which is a varicap assemblage composed of a plurality of varicaps connected in parallel, wherein

• each of the varicaps is an MOS capacitor produced under a common and single process condition;
• each of the varicaps has
• a conductor layer serving as a second electrode and formed via a capacitance insulating film on a first conductivity-type semiconductor substrate serving as a first electrode,
• a second conductivity-type impurity region formed near a surface in proximity to a region of the first conductivity-type semiconductor substrate opposing the conductor layer, and
• a first conductivity-type high concentration layer formed near a surface only in the region opposing the conductor layer so as to be fully covered with the conductor layer on the first conductivity-type semiconductor substrate;
• and
• each of the varicaps is configured such that a capacitance value as a capacitance element between the first conductivity-type semiconductor substrate serving as the first electrode and the conductor layer serving as the second electrode is changed by applying a control voltage to the conductor layer while applying any one of a plurality of types of direct-current voltages, which serve as reverse voltages of a diode composed of the first conductivity-type semiconductor substrate and the second conductivity-type impurity region and which have different voltages, to the second conductivity-type impurity region.