PURPOSE: To detect signals with comparatively simple configuration by deciding the presence/absence of the signal to be detected based on the output of a comparator circuit.
CONSTITUTION: The above circuit is the digital signal detection circuit to be used for detecting dial tone signals and multifrequency signals or the like in a key telephone system, and the presence/absence of the signal is detected not according to the level of the signal to be detected but according to the outputs of first and second sample circuits 8 and 9 having phase difference. In this case, a decision circuit 11 for deciding the presence/absence of the signal to be detected based on the output of a comparator circuit 10 is connected to an output line 37 of the comparator circuit 10 and an output line 34 of a PLL circuit 7 and transmits the decision output to a line 24. Thus, various signals can be detected by the signal detection circuit of the same circuit configuration.
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KAWASHIMA MASAYUKI
ICHIMURA KOICHI
YAMAGUCHI NAOYUKI
