BINARIZING CIRCUIT

PURPOSE:To improve the accuracy by expanding a noise superimposing part of a comparator input from a hysteresis area so as to generate a same binary output at all times even when noise is superimposed onto an input signal or the like and an input signal level is contained in the hysteresis area. CONSTITUTION:Since a noise pulse VSN is injected to a feedback input of an operational amplifier 20, a waveform of a signal outputted from the operational amplifier 20 is a waveform in which a noise pulse VSN is superimposed onto a video signal. Thus, even when a level of the input signal of a comparator 10 stays in a period of mark * less than a range of a hysteresis and stays in a period of mark ** increased in the range of hysteresis, since the superimposed noise pulse VSN exceeds the area of the hysteresis, the result of discrimination is both '1'. Thus, the waveform is a waveform resident in the range of the hysteresis from a high signal level for both the periods. Then the video signal whose signal level stays in the hysteresis range is converted into a digital value '1' to prevent change in colors after and before the printed character.