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US 4,439,639 AGranted
Digital circuit and method for the detection of call progress tones in telephone systems
AssigneeNorthern Telecom Limited
InventorErnst A. Munter
Life of this patent
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AssigneeNorthern Telecom Limited
InventorErnst A. Munter
Estimating the term…
A digital tone detector circuit characterizes the received PCM encoded signals as one of a plurality of call progress tones, voice signals or silence. The PCM signal is linearized and normalized to a predetermined level in a digital automatic gain control circuit which also provides a signal corresponding to the level of the input signal. A first circuit is responsive to the linear signal for providing a count of the zero level traversals incurred by the linear signal. An envelope detector circuit is also responsive to the linear signal for providing a signal representing the envelope frequency thereof. The composite results corresponding to the signal level, the zero-level traversal count, and the envelope frequency are translated in an evaluation logic circuit to provide an output signal representing the identity of the input PCM signal. A microprocessor is responsive to a plurality of the output signals from the devaluation logic circuit for determining the cadence of the received PCM signals.
A circuit for determining the identity of a call progress tone in a telephone system, comprising:
A method of determining the identity of a signal appearing on a telephone line in a system, comprising the steps of:
A method for determining the identity of a PCM encoded input signal comprising the steps of:
A digital circuit for detecting the identity of PCM encoded call progress tone signals in a telephone system comprising, a microprocessor for receiving the tone signals, a digital tone detector circuit for characterizing the tone signals as voice signals, silence or one of a plurality of call progress tones, the digital tone detector comprising, a digital automatic gain control circuit for measuring the level of the tone signals and for linearizing and normalizing the received tone signals to a predetermined level, a first circuit for counting the zero-level traversals incurred by the linear PCM signal, an envelope detector circuit for providing signals corresponding to the envelope frequency of the linear PCM signals, and an evaluation logic circuit responsive to the level signals from the automatic gain control circuit and to the zero-level traversals count from the first circuit as well as from the signals corresponding to the envelope frequency of the linear PCM signal for providing an output signal identifying the received PCM tone signal as one of a plurality of progress tones, voice signals or silence.
A digital tone detector circuit for characterizing PCM encoded tone signals as one of a plurality of call progress tones, voice or silence, comprising:
Dependencies are inferred from the claim text.