| 摘要 |
PURPOSE:To assure the binary coding regardless of a change of light volume which is caused by the fluctuation of the power supply of a light source, by detecting both black and white peak values of an analog picture signal and dividing the output voltage of one side to apply it to a time constant circuit of the other side. CONSTITUTION:An analog picture signal VIN obtained by giving the photoelectric conversion to an original is applied to a white peak value wave detecting circuit 2 and a black peak value wave detecting circuit 3'. The black peak value voltage VSL holds the black peak value when the signal VIN has a big change and is limited for its upper limit level by the voltage (equivalent to 80% white peak value voltage VSH) which is decided by resistances 17 and 18 when the signal VIN has a small change like the case when the white signal is continuous. Thus the VSL is always lower than the VSH to any kind of picture signal. As a result, the threshold voltage VS is always steady to the signal VIN to ensure the accurate binary coding. |
