Patent ID: 7091797

Claim:
A MOS-type variable capacitance element comprising: a semiconductor substrate of a first dopant type; low-concentration diffusion region of a second donant type opposite to polarity of the semiconductor substrate formed in the semiconductor substrate; a source region of the first dopant type and formed in said low-concentration diffusion region; a drain region of the first dopant type formed in said low-concentration diffusion region; a high-concentration diffusion region of the second dopant type formed in the low-concentration diffusion region; a gate oxide film formed on the low-concentration diffusion region; a gate electrode is formed on the gate oxide film; a reference potential source; a first electrode which connects the source and drain regions to the reference potential source; a capacitance controlled circuit having a capacitance controlled input; a second electrode which is connected to the gate electrode and does not form an electrode connection to said first electrode, the second electrode being connected to the capacitance controlled input; a control voltage input accepting a control voltage which is variable; and a third electrode connected to the high-concentration diffusion region and the control voltage input for accepting the control voltage in a range having polarity equal to polarity of the first dopant type of the semiconductor substrate to the high-concentration diffusion region using the reference potential as a reference, wherein a variable capacitance element is provided between the second electrode and the third electrode.