| 摘要 |
PURPOSE: An AMP having gain control capacity is provided to adjust the gain conveniently by giving a voltage to the AMP from an external source. CONSTITUTION: In the AMP having gain control capacity, a differential amplifier(10) produces an output signal(Output) proportionate to the input signal difference and includes three NPN transistors(Q1,Q2,Q5), two PNP transistors(Q3,Q4), and two resistors(R2,R3). A current supplying unit(20), including a resistor(R1), two diodes(D2,D1) and a NPN transistor(Q6), provides the differential amplifier(10) with a reference current(Iref). A variable-current supplying unit(30), including two PNP transistors(Q9,Q10), a resistor(R4) and two NPN transistors(Q7,Q8), controls the gain by varying the reference current(Iref) of the differential amplifier(10).
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