| 摘要 |
PURPOSE:To make it possible to maintain the input-output impedance under almost constant condition at an attenuator circuit, by adjusting the variation of pin diode which is used at the attenuator circuit with resistance. CONSTITUTION:Attenuator circuit 7 using pin diodes 5 and 6 is connected to the back of primary stage transistor TR3 through matching transformer 8, and the 2nd stage transistor TR9 is connected to the back of the attenuator circuit. When the input level is raised from the lower condition to higher condition, the AGC voltage at terminal 23 becomes higher, and at TR3 the emitter current is increased and the gain is lowered. On the other hand, at circuit 7 the current flowing into diode 5 is reduced and the current flowing into diode 6 is increased, internal resistance of diode 5 is increased and that of diode 6 is reduced. By this, by adjusting variation of diodes 5 and 6 skillfully with resistances 12 and 13, the input-output impedance can be maintained under almost constant condition at circuit 7. |
