| 摘要 |
PURPOSE:To reduce errors of a decoded control signal by closing a data gate if >=1 prescribed condition is not satisfied when transmitting the control signal in H pulses during vertical blanking periods of a TV signal. CONSTITUTION:An FSK signal (c) which is extracted by BPF1 and contains a noise is passed through a carrier level discriminating circuit for amplification 2, rectification 3, and voltage comparison 4 to output a signal (f), and also passed through a limiter 5, a frequency discriminating circuit 6, and an LPF7 to output a demodulating signal (d). The signal (f) is supplied to one input terminal of an AND circuit, and the signal is applied to the other terminal through a voltage comparing circuit 9 and a time deciding circuit 10. The output of this circuit 23 is sent to a data gate 11. Further, voltage comparing circuits 15 and 16, an NOR circuit 17, and the AND circuit 18 discriminate whether the absolute value of the output signal of an FSK signal democulating circuit is greater than a certain value at a sampling point. Then, a gate 11 is closed when the carrier level of the signal (f) is less than the certain value, when the signal (d) does not reach an expected value for a certain time, or when the absolute value of the output signal is less than the certain value. |
