| 摘要 |
PURPOSE:To adjust the total amount of bias current and the bias current balance by detecting an average bias voltage of a push-pull output stage, comparing it with a setting value and applying negative feedback to the input side, and detecting a difference in currents flowing to single conductive elements constituting the push-pull output stage so as to apply negative feedback to the input side. CONSTITUTION:An input signal is inputted from an input terminal 22, led to the 1st stage differential amplifier 24 comprising Tn TR1, TR2 and inputted to a push-pull output stage 32 comprising Nch MOS-FETs 28, 30 via the next stage differential amplifier 26 comprising Tr TR4, TR5. The average gate bias voltage is adjusted automatically to a setting voltage Vr by applying DC negative feedback through an operational amplifier A2 and the total bias current at the output stage 32 is made constant in response to the reference voltage Vr. Further, an output signal of an operational amplifier A1 is fed back to the base of the Tr TR2 constituting the 1st stage differential amplifier 24. Since this loop constitutes the negative feedback, it acts like zeroing the difference thereby balancing the bias currents of the MOS-FETs 28, 30. |
