Digital decoder for multiple frequency telephone signalling

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

H - Electricity

04

M

379/21, 354/92

H04M 1/50 (2006.01) H04Q 1/457 (2006.01)

Patent

CA 1058784

Abstract of the Disclosure 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.

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