| 摘要 |
In an amplifier circuit, a main amplification section includes an amplifier for amplifying an input signal and a reference voltage generation circuit for generating a reference voltage from an output signal of the amplifier. Other main amplification sections each including the same internal structure are cascade-connected. A switch is provided for selecting any of amplifier outputs of these main amplification sections. A frequency component lower than that of an input signal to the amplifier circuit is removed by a filter circuit, and thereafter, the presence/absence of an input signal is detected by an amplitude detection circuit and a comparator. With such a structure, even if the input signal abruptly changes, e.g., immediately after the start of communication or immediately after the end of communication, an optical signal input is correctly detected and reproduced.
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