TELEPHONE CALL PROGRESS TONE AND ANSWER IDENTIFICATION CIRCUIT

摘要

TELEPHONE CALL PROGRESS TONE AND ANSWER IDENTIFICATION CIRCUIT Disclosed is a call progress tone detection circuit for determining whether an incoming telephone signal is a call progress tone and for identifying such call progress tone. The circuit includes an envelope detector for receiving a signal and for developing an envelope signal representative of the envelope of the received signal. The call progress tone detection circuit extracts the low frequency envelope of the received signal and examines its period. These period measurements are accumulated and then evaluated. If the envelope period is not reasonably constant over a standard measurement interval, then the call progress tone detection circuit can conclude that the received signal is voice. However, if the envelope period is regular, then the call progress tone detection circuit according to the preferred embodiment of the present invention will compare the detected envelope period and other timing parameters of the signal to known periods and corresponding parameters for signals used by the various telephone systems in current use. If there is a match between the detected parameters, then the call progress tone detection circuit identifies the call progress tone for further use by the automatic telephone caller.