| 摘要 |
PURPOSE:To obtain zero detecting pulses of the frequency twice that of the AC waveform used for a tape recorder of an FM recording and reproducing system relatively easily by using a zero cross detector detecting zero crossing, a delay circuit, and logical circuits. CONSTITUTION:When a sinusoidal AC waveform (reproduction FM signal) A is inputted to a comparator 16 by reading data from a tape 11, it is compared with the zero level at the inversion input terminal, and a zero cross detection signal B which is waveform-shaped to a square wave is obtained. This signal B is phase-inverted by an inverter 17, and is delayed by the time T in a delay circuit, whereby an inverted delay signal C is formed. Next, in an exclusive OR circuit 19, the exclusive OR of the signal B and the signal C is determined and an exclusive OR output signal is obtained. This signal D is phase-inverted with an inverter 20, and the zero cross detection pulse E of the frequency twice that of the zero cross of the AC waveform is obtained in synchronization therewith. In this way, the relatively simple circuits are constituted without using any monostable multivibrator. |
