| 摘要 |
PURPOSE:To suppress the influence of the dispersion of a constituting element upon gain control by connecting the collector-emitter currents of two transistors (TR) be tween the input terminal of a current mirror circuit and a standard point in series, and supplying a current obtained at the output terminal of the current mirror circuit to P-N junctions, respectively provided in two TR emitters. CONSTITUTION:A constant voltage is supplied to the base of the TR 36 from a voltage source 7 as a prescribed bias voltage. A gain control current to flow through the collector-emitter current paths of the TRs 36, 38, takes a value that the voltage of the power source 7, from which the voltage between the base and the emitter of the TR 36 and the output of a comparator 19 are subtracted, is divided by a resistance 37. Owing to that the said current flows into diodes 1 and 2 through the current mirror circuit, the operating resistances the diodes 1 and 2 vary, and perform the gain control. Now, when an input signal from a signal source 12 increases and the output of the comparator 19 increases, since the emitter voltage of the TR 38 comes higher, the gain control current comes smaller. As a result, the current, flowing into the diodes 1 and 2, comes smaller, the operating resistances of the diodes come larger. According ly, the gain fluctuation of a differential amplifier can be suppressed to be small.
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