| 摘要 |
<p>An automatic gain control circuit comprising a gain-controlled amplifier for receiving a variable amplitude, pulse-type input signal to produce a substan-tially constant amplitude, pulse-type output signal which is applied to a feedback circuit for comparison with a predetermined reference voltage to generate n control voltage to set the gain of the amplifier. A voltage limiter included in the feedback circuit clips the pulse peaks of the output signal whenever the peaks exceed a predetermined amplitude so that the gain of the amplifier is reduced in a prescribed manner to preclude output signal dropout. A peak detector and a filter included in the feedback circuit are capable of operating in fast and slow modes. When operating in the fast mode, the peak detector responds essentially to each pulse peak of the output signal and the filter has a wide bandwidth so that the automatic gain control circuit operates with a prescribed fast time response. When operating in the slow mode, the peak detector operates to increase the gain of the amplifier slowly in order to limit output signal overshoot and preclude output signal dropout if the input signal reappears after an absence for some period. The filter, when operating in the slow mode, has a narrow bandwidth so that the automatic gain control circuit operates with a time response substantially slower than the fast time response. A controller circuit produces, in response to the output signal, a controller signal which causes fast mode operation of the peak detector and filter whenever the output signal is present and slow mode operation thereof whenever the output signal is absent for a predetermined time period.</p> |
