Filter and multiplexer

A filter, comprising:

• a filter circuit;
• and
• an additional circuit connected in parallel with at least a portion of the filter circuit;
• wherein
• the additional circuit includes a first IDT electrode group and a second IDT electrode group connected in multiple stages between a first input/output terminal and a second input/output terminal;
• the first IDT electrode group includes a first interdigital transducer (IDT) electrode and a second IDT electrode that are side by side in a propagation direction of an acoustic wave;
• the second IDT electrode group includes a third IDT electrode and a fourth IDT electrode that are side by side in the propagation direction of the acoustic wave;
• a first end of the first IDT electrode is connected to the first input/output terminal;
• a first end of the third IDT electrode is connected to the second input/output terminal;
• a second end of the first IDT electrode and a second end of the third IDT electrode are connected in common and connected to a ground;
• a first end of the second IDT electrode and a first end of the fourth IDT electrode are connected in common;
• a second end of the second IDT electrode and a second end of the fourth IDT electrode are connected in common;
• and
• in a direction extending from the first input/output terminal to the second input/output terminal, the first input/output terminal is connected to the first end of the first IDT electrode at a portion of the additional circuit that is closer to the first input/output terminal than to the second input/output terminal.

A filter, comprising:

• a filter circuit;
• and
• an additional circuit connected in parallel with at least a portion of the filter circuit;
• wherein
• the additional circuit includes a first IDT electrode group and a second IDT electrode group connected in multiple stages between a first input/output terminal and a second input/output terminal;
• the first IDT electrode group includes a first interdigital transducer (IDT) electrode and a second IDT electrode that are side by side in a propagation direction of an acoustic wave;
• the second IDT electrode group includes a third IDT electrode and a fourth IDT electrode that are side by side in the propagation direction of the acoustic wave;
• a first end of the first IDT electrode is connected to the first input/output terminal;
• a first end of the third IDT electrode is connected to the second input/output terminal;
• a second end of the first IDT electrode and a second end of the third IDT electrode are connected in common and connected to a ground;
• a first end of the second IDT electrode and a first end of the fourth IDT electrode are connected in common separately from the first and second input/output terminals;
• and
• a second end of the second IDT electrode and a second end of the fourth IDT electrode are connected in common separately from the first and second input/output terminals.