Patent ID: 7460792

Claim:
A receiving circuit, for use in an optical communication, from which an output signal is outputted in accordance with a signal optical pulse incident to a light-receiving element, the receiving circuit comprising: a variable output circuit for detecting a pulse width of the signal optical pulse, selecting one pulse width from a plurality of pulse widths in accordance with the pulse width thus detected, and outputting an output signal having the one pulse width thus selected; the variable output circuit includes a first pulse generating circuit generating a received pulse by comparing an electric signal converted from the signal optical pulse with a threshold, the received pulse being a digital signal; wherein either the received pulse generated by the first pulse generating circuit or a pulse having a different pulse width from that of the received pulse is selectively outputted as an output signal, in accordance with the pulse width of the signal optical pulse; the variable output circuit includes a second pulse generating circuit for generating a signal having a predetermined pulse width corresponding to a low-speed communication; and if it is judged that a pulse width of an output from the first pulse generating circuit exceeds a predetermined value, a signal generated by the second pulse generating circuit is outputted as the output signal, instead of outputting the received pulse; and the variable output circuit includes (I) a trigger generating circuit for generating a trigger signal when a pulse generating time of the first pulse generating circuit exceeds a first predetermined period, and (II) a timer circuit for generating a pulse having a second predetermined period, in response to the trigger signal from the trigger generating circuit; if the timer circuit outputs no pulse, a pulse outputted from the first pulse generating circuit is outputted as the output signal; and if the timer circuit outputs a pulse, a pulse outputted from the second pulse generating circuit is outputted as the output signal.