| 摘要 |
A crystal filter network comprises at least one variable impedance network (103a, 103b), at least one crystal filter (103c), and a control circuit (110). Each variable impedance network (103a, 103b) has a control terminal, a first terminal (37, 39), and a second terminal (38, 40) for connecting a first impedance (113) coupled to the first terminal (37), to a second impedance coupled to the second terminal (38). The crystal filter (103c) is coupled to at least one of the first and second terminals. Coupled to the control terminal, the control circuit (110) electrically varies (V1 and V2) the variable impedance network (103a, 103b) to provide a predetermined impedance characteristic to the crystal filter network (103c).
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