| 摘要 |
An AGC system for controlling the gain of an amplifier includes an AGC multiplexer and an AGC circuit. The AGC circuit receives an input signal from the AGC multiplexer and generates, in response thereto a gain control signal. The AGC multiplexer operates in three modes. In a first mode, in which the erased portion of a sector is being detected, the AGC multiplexer couples an input preset signal of a predetermined voltage level to the AGC circuit, enabling it, in turn, to generate a gain control signal to control the gain to a predetermined level. In a second mode, the AGC multiplexer couples a signal related to the output signal from the amplifier to the AGC circuit, enabling the AGC circuit to generate a gain signal related to the output level of the amplifier. In the third mode, the AGC multiplexer maintains its output signal constant, thus enabling the AGC circuit to maintain its gain control constant.
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