| 摘要 |
PURPOSE:To obtain a desired frequency characteristic by changing a control voltage source so as to change simultaneously the capacitance of a varactor diode thereby changing the tuning frequency of two turning circuits whose sharpness is set differently respectively in opposite directions at the same time. CONSTITUTION:An IF signal incoming to an input terminal 15 is amplified by a transistor (TR) TR1 and fed to tuning circuits 13, 14, where dual tuning is taken with tuning frequencies f1, f2, the impedance is converted by a TR2 and the result is extracted from an output terminal 16. Since the tuning circuits 13, 14 are provided respectively with varactor diodes C1, C2 in this case, when the voltage of a control voltage source V3 is changed, the tuning frequencies f1, f2 are changed in opposite directions with the same ratio at the same time. An F characteristic (frequency characteristic) shown in (B) is obtained at f1=f2=f0 for example, the F characteristic shown in (A) is obtained with f1<f2, an the F characteristic shown in (C) is obtained at f1>f2.
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