| 摘要 |
PURPOSE:To always set an output signal level with no optical signal given thereto to either a low level or a high level by generating a single pulse at application of power. CONSTITUTION:A positive single pulse is generated from a single pulse generating circuit 5 at application of power and its single pulse is given to a differentiation circuit 3. The differentiation circuit 3 generates a positive pulse at the rising of the single pulse and generates a negative pulse at the falling of the single pulse and gives the result to a hysteresis comparator 4. The hysteresis comparator 4 has a hysteresis width in a threshold value, keeps a high level when an input signal exceeds the hysteresis width and reaches a positive threshold value or over and keeps a low level when the input signal is below the negative threshold value and keeps the preceding output level when the input signal is within the hysteresis width. Thus, the output level at application of power is set to either the low level or the high level. |
