| 摘要 |
PURPOSE:To improve an operation in a microwave frequency range by equipping a feedback circuit to feedback the output of a reference cell to the gate of the electric field effect transistor (FET) of an attenuating cell and the reference cell. CONSTITUTION:A reference attenuating cell 12 executes the feedback control of a main attenuating cell 10 through an operational amplifier 14 and this reference cell 12 is designed so as to be electrically equivalent with the attenuating cell 10 in a characteristic impedance. A control signal that an amplifier 60 outputs to an output conductor 38 is changed by an attenuation control signal impressed to the reference output signal of an NORD 44 and a control terminal 16. This control signal is fedback to the gate of a parallel FET 54 and controls a reference circuit operation and the impedance of the NORD 44 is made equal to that of a NORD 46. Since the same control signal is impressed to an FET 34, the attenuating cell 10 and the reference cell 12 are samely operated. Thus, regardless of the change of the attenuating quantity of an attenuator, since the characteristic impedance can be always maintained to be constant, the characteristic is stabilized over a wide range.
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