Digital decoder for multiple frequency telephone signalling

Details Digital decoder for multiple frequency telephone signalling Digital decoder for multiple frequency telephone signalling

1976-06-02

1977-08-23

Claffy, Kathleen H.

H04M 150

Patent

active

040442063

ABSTRACT:
A multiple-frequency decoder which measures the two-tone output from a multiple-frequency dial type telephone and identifies what number was dialed. A unique binary code is produced as a timed output for each number dialed. In addition, the decoder has provision for detecting and providing as a separate output a unique binary output word whenever a preselected transfer digit, e.g., a 1, 2 or 3 is dialed. With this additional output data, transfer relays can be operated. The decoder inputs are derived from high and low pass filters. The decoder differentiates between valid multiple-frequency tones and extraneous noise, such as voice signals, completely digitally, as follows: once the digital measurement of one cycle of each of the multiple incoming frequencies is made, the combination of all frequency measurements is stored as a k-bit binary word. In order for an incoming signal to be considered valid, the same k-bit binary word must occur n consecutive times, where n is preselected based on the degree of noise immunity required.

REFERENCES:
patent: 3537001 (1970-10-01), Friend
patent: 3582562 (1971-06-01), Sellari
patent: 3760269 (1973-09-01), Beeman et al.
patent: 3790720 (1974-02-01), Schartmann
patent: 3912869 (1975-10-01), Ullakko
patent: 3949177 (1976-04-01), Ball et al.
patent: 3993875 (1976-11-01), Ebner et al.

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