| 摘要 |
PURPOSE:To reduce the circuit scale without providing a filter circuit to integrate the circuit, by providing a pattern generating circuit to detect directly a digitized PB (push button) signal. CONSTITUTION:The PB signal transmitted by a digital signal transmission line has the waveform shaped by a receiving circuit 21 and is applied to a frequency discriminating circuit 22. The frequency discriminated circuit 22 has a shift register 24, a pattern generation circuit 25, and a comparison discrimination circuit 26. The pattern generation circuit 25 generates pulse patterns, which are due to digitizing of the PB signal and whose number corresponds to the number of combinations of two frequencies, and inputs them to the comparison discrimination circuit 26. The comparison discrimination circuit 26 compares the digitized PB signal of the output of the shift register 24 with plural pulse patterns, and an output corresponding to a coincident pattern is applied to a pulse cold generation circuit 23. Thus, the PB signal is detected with a simple constitution without demodulating it to an analogue signal. |
