The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 25, 1976
Filed:
Apr. 07, 1975
Harley Monroe Newsom, Los Gatos, CA (US);
Michael Allen Patten, San Jose, CA (US);
International Business Machines Corporation, Armonk, NY (US);
Abstract
Calling signals for tone-frequency telephone calling and like communications systems are generated in digital form. For the eight tone frequencies used in American telephone systems, a group of about 50 bits (average) for each tone is stored in an electronic store in delta modulation data form. Circuitry according to the invention is arranged for repetitively reproducing the contents of the store to produce a substantially continuous waveform. Bits for one high frequency band tone and one low frequency band tone are selectively reproduced and applied to a delta demodulation circuit for producing the desired tone-frequency analog signal. In a basic embodiment, start-stop operation is used for producing a calling signal for a single switching operation. A continuously operating tone frequency generating circuit embodiment is arranged for producing a multiple of continuously available tone signalling outputs. Both embodiments are readily constructed as Large Scale Integration (LSI) devices and readily arranged with the remainder of the communications lines switching circuit components in a central or branch exchange installation.