| 摘要 |
PURPOSE:To perform gain control by a digital signal by intermitting the output signal of an amplifier through a switch, smoothing and feeding its output signal back to the amplifier, and varying the opening and closing time ratio of the switch. CONSTITUTION:The output signal V0 of the operational amplifier 13 is intermitted through the switch 14. The switch 14 is turned on and off by a gain control signal 16, whose output pulse signal V'0 is smoothed by a smoothing circuit 15 to feed the smoothed signal VF back to an input of the amplifier 13. When the crest value of the signal V'0 is V0, pulse width is (t), and its period is T, signal VF=(t/T)XV0. When the gain of the open loop of the amplifier 13 is sufficiently large, an input signal VI becomes equal to the feedback signal VF, so VI=VF= (t/T)XV0. Therefore, the gain G of the amplifier 13 is equal to V0/VI=T/t and the gain of the amplifier 13 depends upon the duty ratio of the pulse width of the gain control signal 16. |
