| 摘要 |
PURPOSE:To attain excellent characteristic and amplitude versus frequency characteristic by using plural elastic surface wave filters, giving a broad band characteristic to one filter among them, giving a narrow band characteristic to the others so as to make a delay time characteristic equal to a phase characteristic of each filter thereby adjusting the gain of a variable gain element corresponding to a level change of an input signal. CONSTITUTION:An input electrode 2 and an output electrode 3a constitute a notch filter where the band width is + or -6MHz at a center frequency of 50MHz and also an output signal level is attenuated by 3dB at the center frequency. Further, each read-screen electrode is constituted that each delay time is equal and each phase characteristic is arranged. The amplitude versus frequency characteristic of a single broad band output electrode 3a is shown in broken lines 11. Further, solid lines 14 and 18 indicate the overall amplitude versus frequency characteristics viewed from an output terminal 6 and solid lines 15 and 19 depict the phase characteristics. Although the device is used while the gain of the variable gain element is lowered normally, if the high frequency level of the input signal is decreased, the gain of the variable gain element is increased, allowing to obtain a constant signal level at all times thereby attaining high frequency compensation of the signal. |
