| 摘要 |
PROBLEM TO BE SOLVED: To effectively reduce overlapping of high frequency external noises on the emitter node of the transistor in a differential amplifier on the input side of an operational amplifier.SOLUTION: A differential amplifier circuit 10A on the input side comprises: a power source I1 one of the ends of which is connected with a power source terminal 4; transistors Q1 and Q2 the emitters of which are connected in common with the other end of the power source I1; and load resistors R3 and R4 connected between each collector of the transistors Q1 and Q2, and a power source terminal 5, respectively. A base-grounded amplification circuit 20A comprises: a transistor Q3 the emitter of which is connected with the collector of the transistor Q2; a transistor Q4 the emitter of which is connected with the collector of the transistor Q1; a base resistor R5 connected between the bases of the transistors Q3 and Q4 and the power source terminal 5; and a transistor Q5 which supplies a base current to the transistors Q3 and Q4. In an operational amplifier including the above two circuits, a high-pass filter circuit comprising a capacitor Cb and a resistor Rb is connected between the collector of the transistor Q3 and the power source terminal 5. |
