Patent ID: 6940964

Claim:
A push-button signal receiving circuit for receiving a push-button signal and identifying a dialed number based on the received push-button signal, comprising: first and second frequency detecting portion provided respectively for low- and high-frequency identification signals included in the received push-button signal, for detecting frequencies of input signals over one or more periods thereof to extract the identification signals; third and fourth frequency detecting portion provided respectively for the low- and high-frequency identification signals included in the received push-button signal, for detecting the frequencies of the input signals over a number of periods greater than that of said first and second frequency detecting portion, to extract the identification signals; valid signal determining portion for determining whether the received push-button signal is valid or not based on results of determination as to coincidence of continuance times of the identification signals extracted by said first and second frequency detecting portion, coincidence of the frequencies detected by said first and third frequency detecting portion, and coincidence of the frequencies detected by said second and fourth frequency detecting portion; and dialed number output portion for outputting the dialed number based on the detected low and high frequencies if the push-button signal is judged valid by said valid signal determining portion, wherein said first, second, third and fourth frequency detecting portion each measure a time required until the number of times the signal level of the input identification signal crosses a threshold reaches a predetermined number, determine whether or not the measured time falls within an allowable time range, and detect the frequency of the identification signal, and wherein the allowable time range set in said first and second frequency detecting portion per period of the identification signal is wider than that set in said third and fourth frequency detecting portion.