Abstract: A directional coupler that has a degree of coupling that is close to constant and is to be used in a predetermined frequency band includes a main line between a first outer electrode and a second outer electrode. A sub-line is provided between a third outer electrode and a fourth outer electrode and is electromagnetically coupled with the main line. A low pass filter is provided between the third outer electrode and the sub-line and has a characteristic in which attenuation increases with increasing frequency in a predetermined frequency band.

Abstract: A balanced-to-unbalanced transformer includes a +90° phase shift circuit, which is disposed between a branch point connected to an unbalanced terminal and a first terminal, and a ?90° phase shift circuit, which is disposed between the branch point and a second terminal. A first inductor is connected between the first terminal and a power supply terminal, and a second inductor is connected between the branch point and the power supply terminal. A power-supply-terminal-side capacitor is connected in shunt between the power supply terminal and a ground. A second-terminal-side series inductor is connected in series between the branch point and the second terminal.

Abstract: A balanced-to-unbalanced transformer includes a +90° phase shift circuit, which is disposed between a branch point connected to an unbalanced terminal and a first terminal, and a ?90° phase shift circuit, which is disposed between the branch point and a second terminal. A first inductor is connected between the first terminal and a power supply terminal, and a second inductor is connected between the branch point and the power supply terminal. A power-supply-terminal-side capacitor is connected in shunt between the power supply terminal and a ground. A second-terminal-side series inductor is connected in series between the branch point and the second terminal.

Abstract: An oscillator includes an oscillating active element having a first main electrical-current path, a buffer-amplifying active element that is of the same type as the oscillating active element, the buffer-amplifying active element having a second main electrical-current path, and a load impedance for the buffer-amplifying active element. The first main electrical-current path, the second main electrical-current path, and the load impedance are connected in series between a power-supply terminal and ground in that order, and the node of the buffer-amplifying active element and the load impedance is a signal outputting point.

Abstract: A piezoelectric oscillator includes a piezoelectric element, and an oscillation circuit connected to one of two terminals of the piezoelectric element. One terminal of first capacitance element of which the other terminal is grounded is connected to at least one of the two terminals of the piezoelectric element. A series circuit including a resistor, which has adjustable resistance, can be adjusted and a second capacitance element is connected in parallel to the first capacitance element.

Abstract: An oscillator includes an oscillating active element having a first main electrical-current path, a buffer-amplifying active element that is of the same type as the oscillating active element, the buffer-amplifying active element having a second main electrical-current path, and a load impedance for the buffer-amplifying active element. The first main electrical-current path, the second main electrical-current path, and the load impedance are connected in series between a power-supply terminal and ground in that order, and the node of the buffer-amplifying active element and the load impedance is a signal outputting point.

Abstract: A piezoelectric oscillator includes a piezoelectric element, and an oscillation circuit connected to one of two terminals of the piezoelectric element. One terminal of first capacitance element of which the other terminal is grounded is connected to at least one of the two terminals of the piezoelectric element. A series circuit including a resistor, which has adjustable resistance, can be adjusted and a second capacitance element is connected in parallel to the first capacitance element.