| 摘要 |
PURPOSE:To enable to select the range of gain control simply without level shift, by inserting a resistor between the base and ground of the differential transistor circuit. CONSTITUTION:When the switch SW is OFF, the diodes D1, D2 are also OFF, and the control voltage fed between the bases of the differential transistors Q1, Q2 is the voltage divided with the resistors R1 and R3. When the switch SW is ON, the diodes D1, D2 are also ON and the resistors R4, R5 are connected to the base of the differential transistors Q1, Q2. In this case, the control voltage is inserted to the resistor R1 parallelly to the resistors R2, R4, R5. Since the value of parallel resistance by the resistors R2, R4, R5 when the switch SW is ON, is smaller than the value of the resistor R1, the control voltage fed to the base can be made smaller in comparison when the switch SW is OFF, resulting in narrower range of the gain control. |
