H - Electricity – 04 – M
Patent
H - Electricity
04
M
379/57
H04M 3/22 (2006.01) H04Q 1/448 (2006.01)
Patent
CA 1185027
Abstract of the Disclosure 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 evaluation logic circuit for determining the cadence of the received PCM signals.
458800
Nortel Networks Limited
Turpin F.
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