| 摘要 |
PURPOSE:To prevent the saturation even for a large-amplitude input signal by using current control variable resistance elements as gain determining resistances which are connected in series to differential transistors (TR) of one differential amplifier and determine a degree of amplification. CONSTITUTION:Current control variable resistance elements 21 and 22 whose resistance values are reduced in accordance with the increase of current are used as gain determining emitter resistances which are inserted in series to differential TRs Q3 and Q4 in the second differential amplifier 2 having a lower degree of amplification. If a voltage Vc of an external control signal is reduced from the state of Vc=V1 and only the second differential amplifier 2 is operated mainly, both resistance values are reduced to obtain a high gain because currents flowed to resistance elements 21 and 22 are increased. If the external control voltage Vc is increased from the state of Vc=V1, resistance values of both resistance elements 21 and 22 are increased because the current flowed to the second differential amplifier 2 is reduced. |
