JPS5713843A - Signal detecting circuit - Google Patents

Abstract

PURPOSE:To make a signal detecting circuit tolerant to disturbance, such as a noise and short break, and stable under in-use conditions and to eliminate the need for its adjustments by discriminating signal frequencies digitally and by providing a critical threshold level L with which only when L out of M decisions are made correctly, the signal is considered to the detected. CONSTITUTION:Since there are several reception frequencies, set value widths are given to comparators 19 without overlapping mutually and the count value of a (k) counter 10 is inputted. When the input value is within some set value width, its output is signified. Therefore, a pulse 1 (15) rises, the output of a comparator corresponding to a received signal is signified. This output is sampled by an AND circuit 20 by using a pulse 2 (15) to advance only a ''1'' counter 12. Simultaneously, an (m) counter 13 is driven with a pulse 3 (17) to store the completion of this cycle, and the counter 10 and a timing circuit 11 are reset. This cycle is repeated as many times as M and if the frequency where the count value of the (k) counter within the set value width exceeds L, the decision that this signal is received is made.