| 摘要 |
PURPOSE:To avoid a DC level fluctuation by converting a pulse signal attended with the DC level fluctuation into a positive/negative signal at a front edge and a tail end edge so as to eliminate the DC level fluctuation and discriminating the level with a comparator means having a hysteresis characteristic for positive and negative threshold levels so as to provide an output of a rectangular wave signal. CONSTITUTION:A series circuit comprising, a PIN photo diode 5 and a resistor 6 is connected between a power supply voltage point Vcc and ground, the diode 5 receives an optical signal and makes photoelectric conversion and the resulting current signal is fed to a high pass filter 7. The filter 7 converts the signal into a positive/ negative signal at the front edge and the tail end edge of the signal similarly to the case with a differentiation circuit 3, the resulting signal is given to an amplifier 8, in which the signal is amplified and the amplified signal is given to a hysteresis comparator 4, in which the level is discriminated from the output of the filter 7 by using positive negative threshold levels thereby providing a rectangular wave signal as an output where the DC level fluctuation is avoided, Thus, the DC level fluctuation giving an adverse effect such as pulse width, error rate and dynamic range onto the decoding of the rectangular wave is avoided. |
