Telephonic communications – Echo cancellation or suppression
Reexamination Certificate
2000-01-13
2004-09-21
Isen, Forester W. (Department: 2644)
Telephonic communications
Echo cancellation or suppression
C381S071800, C381S071110
Reexamination Certificate
active
06795551
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to telephone subscriber terminals, and in particular, to telephone subscriber terminals intended for receiving and processing in-band FSK signals, such as spontaneous call waiting identification (SCWID) information, during off-hook operation.
2. Description of the Related Art
Telephone service providers offer call feature information such as SCWID to many of their subscribers. To take advantage of such a feature, the subscriber uses special terminal equipment which processes the data, typically in the form of incoming in-band frequency-shift keyed (FSK) signals. These FSK signals are decoded to extract the feature data which are then displayed on some form of terminal display to identify the calling party. With this information available the subscriber can choose to ignore the new call, terminate an existing call and accept the new call, or place the existing call on hold and pick up the new call. (Other examples of call feature data offered by service providers include cash-card “charging” via a telephone terminal.) While features such as SCWID may be desirable, the means by which such a feature is provided does present a problem. The need to use in-band FSK signals to provide this service results in annoying data signals reaching the reception transducer (i.e., handset speaker) which disturb the incoming voice signals and are annoying to the terminal user, or subscriber.
The conventional technique of preventing these in-band FSK signals from annoying the terminal user is to mute the transducers of the terminal for the duration of the FSK signal reception. This approach, however, has the disadvantage of also muting or blocking reception of the voice or background noise information also being received as part of the telephone call. Hence, the user feels “disconnected” during this muting interval. Indeed, if the muting interval is too long, the user may believe that the call has become disconnected and will hang up. Such a technique is disclosed in U.S. Pat. No. 5,263,084 (the disclosure of which is incorporated herein by reference) in which a method is described for handling SCWID information by using a special telephone with the ability to mute the transducers in order to prevent the annoying in-band FSK tones from reaching the handset. Similarly, U.S. Pat. No. 5,768,367 (the disclosure of which is incorporated herein by reference), provides an adjunct that removes the in-band FSK signals from the voice reception path by removing all AC signals, thereby having the same effect as muting the reception transducer.
Accordingly, it would be desirable to have a circuit for blocking reception of the in-band FSK signals by the reception transducer of a telephone subscriber terminal without requiring muting of such reception transducer.
SUMMARY OF THE INVENTION
A circuit for blocking reception of in-band FSK signals by the reception transducer of a telephone subscriber terminal without requiring muting of the reception transducer in accordance with the present invention detects and substantially cancels the incoming FSK signals, thereby leaving the remaining signals, such as voice and background noise unaffected for the terminal user. Additionally, echo cancellation of the user's own voice signal can be provided to prevent interference with detection of the FSK signals.
In accordance with one embodiment of the present invention, a circuit for blocking reception of in-band frequency-shift keyed (FSK) signals by the reception transducer of a telephone subscriber terminal without requiring muting of the reception transducer includes a signal reception path and a FSK signal cancellation circuit. The signal reception path is configured to convey a telephone reception signal for conversion by a telephone reception transducer, wherein the telephone reception signal includes voice and FSK signal components. The FSK signal cancellation circuit, coupled to the signal reception path, is configured to substantially cancel the FSK signal components without interrupting the conveyance of the voice signal component.
In accordance with another embodiment of the present invention, a signal processor for blocking reception of in-band frequency-shift keyed (FSK) signals by the reception transducer of a telephone subscriber terminal without requiring muting of the reception transducer includes: signal reception means for conveying a telephone reception signal for conversion by a telephone reception transducer, wherein the telephone reception signal includes voice and FSK signal components; and FSK signal cancellation means, coupled to the signal reception means, for substantially canceling the FSK signal components without interrupting the conveyance of the voice signal component.
In accordance with still another embodiment of the present invention, a signal processor is programmed for blocking reception of in-band frequency-shift keyed (FSK) signals by the reception transducer of a telephone subscriber terminal without requiring muting of the reception transducer. The signal processor is programmed to perform the steps of: conveying a telephone reception signal for conversion by a telephone reception transducer, wherein the telephone reception signal includes voice and FSK signal components; and substantially canceling the FSK signal components without interrupting the conveyance of the voice signal component.
These and other features and advantages of the present invention will be understood upon consideration of the following detailed description of the invention and the accompanying drawings.
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Kohlmann Renardus Henrikus Maria
Tielens Theo Ary Asmund
Isen Forester W.
National Semiconductor Corporation
Tran Con P.
Vedder Price Kaufman & Kammholz P.C.
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