| 摘要 |
PURPOSE:To detect a data signal securely at any time by leading out the sum output of the positive and negative detection signals of the detected data signal through a loop filter which has a large time constant and thus varying the reference level of a comparator according to the variation in reference level of an input reproduced signal. CONSTITUTION:When the reproduced signal HF of a digital audio disk is supplied to an input terminal 2, the comparator 1 decides on the reproduced signal HF on the basis of a reference voltage V to generate data signals DS of ''H'' and ''L'', which are detected by a positive polarity detecting circuit 3 and a negative polarity detecting circuit 9. The output of the positive detecting circuit 9 and that of the negative polarity detecting circuit 10 are summed up by the adding circuit 10 consisting of resistances 11 and 12 and also biased to a prescribed level by a resistance 13 and outputted. The output signal of the loop filter 14 corresponding to the difference between the reference value Vr of the input reproduced signal HF detected as mentioned above and the reference value VR of the comparator 1 is supplied to an operational amplifier 18 to detect its difference from a zero level, thereby feeding the difference back to the comparator 1 as the reference value VR through voltage limiter circuit 19. |
