Apparatus for detecting pick-up at a remote telephone set

• US 4,477,698 A
• Filed: 09/07/1982
• Issued: 10/16/1984
• Est. Priority Date: 09/07/1982
• Status: Expired due to Term

• Current Assignee: Inventions, Inc.
• Original Assignee: Melita Electronic Labs Incorporated
• Inventors: Szlam, Aleksander, Quinn, Chester P.
• Primary Examiner(s): George, Keith E.
• Application Number:
  US06/415,711
• Time in Patent Office: 770 Days
• Field of Search: 179/5 R, 179/5 P, 179/6.02, 179/6.14, 179/90 BD, 375/120, 375/119
• US Class Current: 379/377
• CPC Class Codes: H04M 1/82 Line monitoring circuits for call progress or status discrimination for detecting caller identity H04M1/573

Abstract

An improved combination of a hardware and digital signal processing filter for detecting pick-up of a telephone call, solely through audio information on the telephone line, is disclosed. The apparatus employs a high gain band pass filter (28) with no automatic gain control, the output of which goes to a window comparator (30). The output from the window comparator (31) goes to a digital high pass filter (32) and from there to an integrator 37 for providing a digital output signal (40) indicative of the presence or absence on the telephone line of a signal exceeding a predetermined magnitude within the filter pass band. The digital signal is then processed by an intelligent digital filter having a set of predetermined threshold values of durations for states of the digital output signal, by which determinations of pick-up are made. The digital filter is adaptive and learns the durations high and low states of the digital output signal as they occur, subsequently checking for deviations from previously learned valid values. The digital filter includes a digital phase lock loop which will lock onto a periodic but asymmetric pattern in the digital output signal and declare pick-up when lock is lost.

Claims

1. In an apparatus for detecting audio signals on a telephone line to detect a pick-up condition on said telephone line, the improvement comprising in combination:

a filter connected to said telephone line including a filter output;

comparator means connected to said filter output for providing a comparator output signal at an output terminal of said comparator in response to signals at said filter output having a magnitude exceeding a predetermined magnitude;

integrating means connected to said output terminal of said comparator means for providing a digital signal in response to the presence of said comparator output signal for at least a predetermined period of time;

adaptive digital filtering means connected to said integrating means and responsive to said digital signal to measure and store as a first learned value the duration of a first occurrence of a first state of said digital signal exceeding a first predetermined glitch duration;

to measure and store as a second learned value, the duration of a first occurrence of a second state of said digital signal, different from said first state, exceeding a second predetermined glitch value,

to measure and store as a third learned value, the duration of a second occurrence of said second state of said digital signal, subsequent to a second occurrence of said first state of said first state of said digital signal,

and further responsive to each Mth occurrence of said second state of said digital signal, M being an odd integer, to provide a pick-up output signal condition when the measured duration of any said Mth occurrence of said second state exceeds said second learned value, and responsive to each Nth occurrence of said second state of said digital signal, N being an even integer, to provide said pick-up output signal condition when the measured duration of any said Nth occurrence of said digital signal exceeds said third learned value.

2. An improved apparatus for detecting audio information on a telephone line to detect a pick-up condition at a called party telephone set comprising in combination:

preprocessing means connected to said telephone line for providing a digital signal in response to said audio information, said preprocessing means being responsive to force said digital signal to a first stage in response to each occurrence of an audio signal on said telephone line within a predetermined pass band for at least a predetermined period of time and for maintaining said digital signal in said first state in response to the continued presence of said audio signal within said predetermined pass band on said telephone, and for forcing said digital signal to a second state opposite said first state in response to a subsequent absence of said audio signal for at least said predetermined period of time,

digital phase locking means connected to preprocessing means and responsive to said digital signal to enter a locked condition in response to said digital signal being characterized by an asymmetric periodicity wherein alternate occurrences of said states are of unequal duration; and

means responsive to said digital phase locking means to provide a pick-up output signal condition in response to said digital phase locking means losing lock on said digital signal.

3. An improved apparatus for detecting audio information on a telephone line to detect a pick-up condition at a called party set comprising in combination:

preprocessing means connected to said telephone line for providing a digital signal in response to said audio information, said preprocessing means being responsive to cause said digital signal to be in a first state when an audio signal within a predetermined passband is present on said telephone line, and to be in a second state opposite said first state when said audio signal with said predetermined passband is absent from said telephone line,

digital signal processing means connected to said preprocessing means and responsive to said digital signal to measure and store each duration of each occurrence of a sequence of occurrences of said first state and said second state, each of said occurrences being of a duration exceeding a predetermined glitch duration, and to compare each said duration measured to a previously stored duration of an occurrence of the same state and to provide a pick-up output signal condition in response to a said duration measured differing from said previously stored duration of said same state by at least a predetermined tolerance value.