Radio-frequency filter, radio-frequency front-end circuit, and communication apparatus

• Main Author: Nosaka, Koji
• Format: Patent
• Language: English
• Published: 08.06.2021
• Subjects: BASIC ELECTRONIC CIRCUITRY; ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS; TRANSMISSION

A radio-frequency filter (10) includes a series arm circuit (11) and a parallel arm circuit (12). The series arm circuit (11) is disposed on a path connecting an input/output terminal (11m) and an input/output terminal (11n). The parallel arm circuit (12) is connected to a ground and to a node (x1) on the path. The series arm circuit (11) includes a series connecting circuit (11e) and a first variable frequency circuit (11a). The series connecting circuit (11e) includes a series arm resonator (s1) and a capacitor (C1). The first variable frequency circuit (11a) is connected in parallel with the series connecting circuit (11e) and varies the anti-resonant frequency of the series arm circuit (11). The first variable frequency circuit (11a) includes a capacitor (C2) and a switch (SW1) connected in series with each other. The series arm resonator (s1) and the capacitor (C1) are connected in series with each other.