| 摘要 |
PURPOSE:To obtain an AGC circuit capable of being miniaturized easily by devising the circuit such that the setting of an automatic control system and the setting of a manual control system are executed by one variable resistor so as to realize the same function as that of a conventional circuit with simpler configuration. CONSTITUTION:With a changeover switch SW thrown to the position of a manual control system N, a prescribed voltage V2 from a reference voltage Vref2 and a fixed resistor R2 is applied to the positive phase input terminal of a low gain differential amplifier A2 as an intermediate control voltage CV2. On the other hand, a voltage V4 applied to the opposite phase input terminal of the low gain differential amplifier A2 is varied with the operation of a variable resistor VR3. Moreover, with the changeover switch SW thrown to the position of an automatic control system A, the output of a high gain differential amplifier A1 is applied to the positive phase input terminal of the low gain differential amplifier A2. A voltage V3 is varied with the operation of the variable resistor VR3. Thus, the control voltage CV outputted from a control voltage generating circuit 2 in both the cases is set optionally by the variable resistor VR3. |
