| 摘要 |
PURPOSE:To prevent deterioration of the maximum photodetecting level. CONSTITUTION:A digital code extending from a start bit to a final bit is shown by a double-current NRZ code of the minimum pulse width TW, and a ternary digital signal B by which periods before and after its digital code both become a zero level is outputted from a ternary signal generator 13. From a modulator 14, pulses (pulse width tW<TW, and the minimum pulse interval is equal to TW) of the number of pieces synchronized with a rise of each positive square wave of the signal B, and also, corresponding to width of its square wave is outputted. From a pulse generator 15, a pulse which is continued from a final bit of the signal B, separated by at least TW from the pulse immediately before, and has larger width than TW is outputted as a zero level display signal D. From a transmitter T, the signals C, D are converted to an optical pulse signal E and transmitted. A signal F converted photoelectrically by a receiver R is converted to a double-current NRZ signal G through a delaying circuit of a delay time tau ( TW-tW) by a demodulator 17. Each pulse width of the signal F is checked by a zero level detector 18, and a zero level detecting signal J is applied to a ternary signal reproducing circuit 19. |
