Circuit arrangement for generating an acoustic ringing signal in a subscriber telephone set

US4723275A · kind A · utility

Assignee

• U.S. Philips Corporation · US

Inventors

• Peter Hirth · Rösrath, DE
• Werner Frerichs · Eckental, DE
• Hubert Grucza · Nürnberg, DE

Key dates

• Filing date: Feb 5, 1986
• Grant date: Feb 2, 1988
• Expiry date: Feb 5, 2006

Classification

• Technology area (CPC H): Electricity
• CPC primary: H04M19/04
• WIPO field: Telecommunications
• WIPO sector: Electrical engineering

Abstract

A subscriber telephone set which comprises a multifrequency dialing tone oscillator, a microprocessor connected thereto for controlling selection of the tones produced thereby, and an acoustic signal element for producing a ringing sound corresponding to ringing tones applied thereto. The microprocessor prevents incorrect triggering of the acoustic signal element by noise voltages on the subscriber line by verifying that the amplitude of the ringing current received on the line exceeds a predetermined level, and also that the ringing current frequency corresponds to the frequency of a resetting signal internally generated within the microprocessor. Upon such verification, the microprocessor controls the dialing tone oscillator to generate a ringing tone which is applied to the acoustic signal element to cause it to generate a ringing sound, the dialing tone oscillator thereby also serving as a ringing tone generator for activating the acoustic signal element.