Dial tone detector

Details Dial tone detector Dial tone detector

1986-12-01

1988-04-12

Dwyer, James L.

Telephonic communications

Supervisory or control line signaling

Signal reception at substation

379386, 379355, 328138, H04M 127

Patent

active

047379847

ABSTRACT:
A dial tone detector is provided possessing a precise definition of a passband. In one example, virtually infinite roll off is achieved in less than 5 hertz. An incoming analog signal of at least a predetermined amplitude is limited to produce square wave pulses which are counted in a first counter over a period of time determined by a periodic RESET signal. A READ signal occuring just before the RESET signal causes either a valid count state or an invalid count state to be stored depending upon the value of the count in the first counter. When a valid count state is in storage, a second counter counts timing pulses while the valid count state persists, whereby in the second counter a count of greater than a predetermined number indicates the presence of dial tone.

REFERENCES:
patent: 3959600 (1975-05-01), Sousa
patent: 4061885 (1977-12-01), Nash et al.
patent: 4142177 (1979-02-01), Davis
patent: 4246445 (1981-01-01), Hayasaka et al.
patent: 4405833 (1983-09-01), Cave et al.
patent: 4439639 (1984-03-01), Munter
patent: 4567328 (1986-01-01), Carrasco et al.
patent: 4675898 (1987-06-01), Bellenger
IBM Technical Disclosure Bulletin, "Call Progress Tone Processor", vol. 29, No. 12, pp. 5571-5573, (May 1987).

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