| 摘要 |
PURPOSE:To improve an SN ratio by providing each circuit block, constituted by using three differential amplifiers, with transistors (TR) whose collector currents are controlled by a variable voltage source. CONSTITUTION:A gain control circuit consists of three differential amplifiers composed of TRs T1-T6, and three differential amplifiers of TRs T7-T12. The voltage of a variable voltage source 2 for gain control is varied to control the differential amplifiers composed of the TRs T3-T12, and thus the gain of a signal inputted from a signal source 9 is controlled to obtain an output at a terminal 3. Under the control of the voltage source 2, the collector currents of TRs T13 and T14 are controlled to control the collector currents of the TRs T3, T6, T9, and T12, controlling the gain of the circuit. |
