| 摘要 |
PURPOSE:To correct an offset voltage without deteriorating the frequency characteristic by connecting a constant current source to a cascode connecting point of a differential amplifier and adjusting the current so as to correct the offset voltage of the differential amplifier. CONSTITUTION:Transistors (TR) Q6, Q7 constituting a constant current source are connected respectively to emitters of TRs Q3, Q4 and a variable resistor RV adjusting a current flowing to the TRs Q6, Q7 is connected between the emitters of the TRs Q6, Q7. A base voltage of TRs Q5-Q8 constituting the constant current source is set by the TR Q8 and resistors R8, R9. An offset voltage appearing output terminals OUT1, OUT2 is corrected by adjusting the resistor RV and making the current flowing to the TRs Q6, Q7 opposite to each other. For example, in selecting the resistor R3 larger than the resistor R4, if an offset voltage takes place, the slider of the resistor RV is moved toward the TR Q7 so as to increase the current flowing to the Q7 more than the current flowing to the TR Q6 and the emitter resistor of the TR Q7 is decreased. |
