| 摘要 |
PURPOSE:To simplify the circuit constitution by using a cathode voltage of 1st and 2nd light emitting diodes for the criterion of the presence of an optical input signal. CONSTITUTION:First and second operational amplifiers 64, 74 discriminate whether a cathode voltage of 1st and 2nd light emitting diodes 63, 73 displaying the presence of a detected voltage of an optical input signal is at a low level or a high level and the result is inputted to a NAND circuit 77 to detect the presence of the optical input signal. That is, not a high frequency but the cathode voltage of the 1st and 2nd light emitting diodes 63, 73 is used for the criterion of the presence of the optical input signal. Thus, a band pass filter or the like is not required and the optical input signal detection circuit with simple circuit constitution is realized. |
