| 摘要 |
PURPOSE:To prevent abnormal operation of a differential amplifier which occurs in case of a great decrease in input signal level, by providing a voltage controlling circuit between the bases of transistors (TR) in a differential couple. CONSTITUTION:A diode D1 as the voltage controlling circuit is provided between the bases of the TRs Q11 and Q12. When the input signal Vin has such a voltage level V1 as shown by V1>=VREF-VF1 (FF1; forward voltage of diode D1), normal differential amplification is performed. On the other hand, the input signal drops in level greatly until V1<=VREF-VF1, a current flows from a reference power source for supplying the VREF to an input terminal T1 through the diode D1 and a resistance R11. Then, a drop in the base potential of the TRQ11 is prevented by the current and no breakdown phenomenon occurs between the base and emitter. Therefore, the normal differential amplification is carried out. Thus, abnormal operation is prevented. In this case, a TR is usable as the voltage controlling circuit. |
