FREQUENCY-VARIABLE FILTER

摘要

A frequency-variable filter includes a filter unit and matching circuits. The filter unit includes frequency-variable resonance circuits that include piezoelectric resonators. The matching circuits have a circuit configuration in which a real number component of an impedance increases as the frequency increases. For example, the matching circuits have an L-type circuit configuration that includes a reactance element connected in shunt to the side of the filter unit and that includes an inductor and a capacitor. As the filter unit includes the piezoelectric resonators, the real number component of the impedance increases as the pass band shifts to a high-frequency side, but the real number component of the impedance increases as the frequency increases in the matching circuits as well. Thus, the impedance matching is achieved

主权项

1. A frequency-variable filter, comprising:
a filter unit having a configuration in which at least one frequency-variable resonance circuit is connected in series to a transmission line or connected between a transmission line and a ground, the at least one frequency-variable resonance circuit including a piezoelectric resonator and a variable capacitor connected to the piezoelectric resonator; a plurality of input-output terminals connected to both ends of the transmission line; and a matching circuit connected between at least one of the input-output terminals and the filter unit, wherein the matching circuit comprises an inductor and a capacitor, and the matching circuit has a circuit configuration in which a real number component of a simultaneous conjugate matching impedance increases as a frequency of a high-frequency signal to be transmitted increases.