In known telephone subscriber end stations a caller_ID IC detects a tone alerting
signal TAS alerting that successive caller_ID information can be received for displaying
on a display of the phone. The known station applies narrow frequency band filters
to detect tones indicating the end of TAS. Such a detection is not flexible as
it can only be used for a specific caller_ID signal protocol.
A flexible detector is proposed which can easily be adapted to widely varying
protocols
and which can also be used for other purposes such as the detection of power drops
in an FSK signal. The detector comprises means for determining a time-domain signal
representing the signal energy of a signal on the subscriber line in a predetermined
time interval.
