| 摘要 |
PROBLEM TO BE SOLVED: To provide a differential surface acoustic wave filter which shows an excellent balun and filter characteristic without the need for increasing the circuit scale more than what is wanted. SOLUTION: When unbalanced electric signals are given between an unbalanced signal input terminal 320 and ground terminals 322, 324, 2-terminal pair surface acoustic wave circuits 302, 304 receive the electric signals. The electric signal received by the circuit 302 is converted into a surface acoustic wave signal and then converted again into an electric signal, and it is given to a 2-terminal pair surface acoustic wave circuit 306. The electric signal given to the circuit 306 is converted into a surface acoustic wave signal and then converted again into an electric signal and fed to a balanced output terminal 350. On the other hand, the electric signal received by the circuit 304 is converted into a surface acoustic wave signal and then converted again into an electric signal, and it is given to a 2-terminal pair surface acoustic wave circuit 308. The electric signal given to the circuit 308 is converted into a surface acoustic wave signal and then converted again into an electric signal and fed to a balanced output terminal 352. In this case, the phase of the output electric signal with respect to the input electric signal in the circuits 302-308 differs by about 180 degrees. Thus, balanced signals with the same phase are outputted from the balanced output terminals 250, 352.
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