| 摘要 |
PURPOSE:To detect a fault irrespectively of reproducing conditions, by detecting the amplitude of an FM signal and changing the threshold of level comparators. CONSTITUTION:An FM signal is converted into a picture signal of base band through a limiter 33 and demodulator 34 and, on the other hand, supplied to level comparators 37 and 38 and previous value holding circuit 39 through an LPF36. The circuit 39 forms a large and small thresholds by dividing its holding voltage and gives the thresholds to the comparators 38 and 37. Moreover, the FM signal is inverted in phase by an amplifier 40 and supplied to a level comparator 42 and previous value holding circuit 43 through an LPF41. The circuit 43 divides its holding voltage and gives the divided one to the comparator 42 as a threshold. Each output of the comparators 38 and 42 is used as fault detected outputs after the OR of the outputs and the output of the comparator 37 is taken through an EX-OR gate. |
