| 摘要 |
PURPOSE:To simplify the circuit constitution and to make accurate the signal level controlling operation, by constituting the circuit with the active element shunting the constant current according to the control signal level, current mirror circuit and differential circuit. CONSTITUTION:If no control input signal is present, equal current flows to the differential transistors Q20, Q21 of the input stage, the collector current of the transistor Q21 is balanced with that of transistor Q27 and the output current of the DC amplifier 13 is zero. If the control input voltage is changed and the base voltage of the transistor Q21 increases, the collector current of the transistor Q21 is decreased accordingly, and the collector current of the transistor Q20 increases by the decrement. The current equal to the collector current of the transistor Q20 flows to the transistor Q26 of the current mirror circuit, and since this current is transferred to the transistor Q27, the current difference between the collector currents of the transistors Q21, Q27 is the output current of the DC amplifier 13 to be the current source of the current switching circuit of the current control attenuator 14. |
