A capacitor having a capacitance settable by biasing, including: a series association of a plurality of first capacitive elements between two first terminals defining the capacitor electrodes; and two second terminals of application of bias voltages respectively connected, via resistive elements, to the opposite electrodes of each of the first capacitive elements.

A resonant circuit includes a resonator having a resonant frequency and an anti-resonant frequency, an inductor connected in series to the resonator, an inductor connected in parallel to the resonator, and a series circuit in which a variable capacitor is connected in series to an inductor (15). The series circuit is connected in parallel to the resonator. The anti-resonant frequency closest to the resonant frequency of the resonator is moved toward higher frequencies or lower frequencies of the resonant frequency on a frequency axis with a variation in the capacitance value of the variable capacitor. With this configuration, a resonator device and a high-frequency filter are provided, in which the relationship between a transmission frequency band and a reception frequency band on the frequency axis is applicable to a variety of multiple communication bands.

A resonant circuit includes a resonator having a resonant frequency and an anti-resonant frequency, an inductor connected in series to the resonator, an inductor connected in parallel to the resonator, and a series circuit in which a variable capacitor is connected in series to an inductor (15). The series circuit is connected in parallel to the resonator. The anti-resonant frequency closest to the resonant frequency of the resonator is moved toward higher frequencies or lower frequencies of the resonant frequency on a frequency axis with a variation in the capacitance value of the variable capacitor. With this configuration, a resonator device and a high-frequency filter are provided, in which the relationship between a transmission frequency band and a reception frequency band on the frequency axis is applicable to a variety of multiple communication bands.

A capacitor has a variable capacitance settable by a bias voltage. A method for setting the bias voltage including the steps of: (a) injecting a constant current to bias the capacitor; (b) measuring the capacitor voltage at the end of a time interval; (c) calculating the capacitance value obtained at the end of the time interval; (d) comparing this value with a desired value; and (e) repeating steps (a) to (d) so as long as the calculated value is different from the set point value. When calculated value matches the set point value; the measured capacitor voltage is stored as a bias voltage to be applied to the capacitor for setting the variable capacitance.

A capacitor has a variable capacitance settable by a bias voltage. A method for setting the bias voltage including the steps of: (a) injecting a constant current to bias the capacitor; (b) measuring the capacitor voltage at the end of a time interval; (c) calculating the capacitance value obtained at the end of the time interval; (d) comparing this value with a desired value; and (e) repeating steps (a) to (d) so as long as the calculated value is different from the set point value. When calculated value matches the set point value; the measured capacitor voltage is stored as a bias voltage to be applied to the capacitor for setting the variable capacitance.

A capacitor has a variable capacitance settable by a bias voltage. A method for setting the bias voltage including the steps of: (a) injecting a constant current to bias the capacitor; (b) measuring the capacitor voltage at the end of a time interval; (c) calculating the capacitance value obtained at the end of the time interval; (d) comparing this value with a desired value; and (e) repeating steps (a) to (d) so as long as the calculated value is different from the set point value. When calculated value matches the set point value; the measured capacitor voltage is stored as a bias voltage to be applied to the capacitor for setting the variable capacitance.

A capacitor has a variable capacitance settable by a bias voltage. A method for setting the bias voltage including the steps of: (a) injecting a constant current to bias the capacitor; (b) measuring the capacitor voltage at the end of a time interval; (c) calculating the capacitance value obtained at the end of the time interval; (d) comparing this value with a desired value; and (e) repeating steps (a) to (d) so as long as the calculated value is different from the set point value. When calculated value matches the set point value; the measured capacitor voltage is stored as a bias voltage to be applied to the capacitor for setting the variable capacitance.

An inductor capacitor (LC) tank includes a first inductor and a first tunable capacitive array. The first inductor has a first terminal and a second terminal, and the first tunable capacitive array has a first terminal and a second terminal. The first tunable capacitive array is at a path branching from a first point between the first terminal and the second terminal of the first inductor, the first terminal of the first tunable capacitive array is coupled to the first point, and the second terminal of the first tunable capacitive array and the second terminal of the first inductor are coupled to a reference voltage.

An inductor capacitor (LC) tank includes a first inductor and a first tunable capacitive array. The first inductor has a first terminal and a second terminal, and the first tunable capacitive array has a first terminal and a second terminal. The first tunable capacitive array is at a path branching from a first point between the first terminal and the second terminal of the first inductor, the first terminal of the first tunable capacitive array is coupled to the first point, and the second terminal of the first tunable capacitive array and the second terminal of the first inductor are coupled to a reference voltage.

An LC parallel resonant element includes a first planar or substantially planar conductor on a first base material layer and second and third planar or substantially planar conductors on second and third base material layers. The first and third planar or substantially planar conductors extend over nearly the entire surfaces of the first and third base material layers. The second planar or substantially planar conductor extends over nearly the entire length of the second base material layer in a second direction such that a space from the other end portion of two end portions of a multilayer body in a first direction is provided. The first and third planar or substantially planar conductors are connected to each other by interlayer conductors near the other end portion of the multilayer body. The first and second planar or substantially planar conductor are connected to each other by interlayer conductors near one end portion of the multilayer body.