| 摘要 |
An apparatus and method for controlling gain automatically uses a light receiving element, a gain amplifier, a difference amplifier, a controller and a variable level circuit. The light receiving element generates electrical signals corresponding to received optical signals. The gain amplifier amplifies the electrial signals and the difference amplifier generates signals corresponding to the difference between defined level of amplified signal and predetermined level. In response to output signals from the difference amplifier, the controller generates signals for controlling gain of the gain amplifier and multiplication factor of the receiving element. The level circuit supplies signals to the receiving element in response to output signals from the controller.
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