Browse Prior Art Database

Automatic Ringback Detector

IP.com Disclosure Number: IPCOM000043007D
Original Publication Date: 1984-Jun-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Federman, E: AUTHOR [+2]

Abstract

This invention relates to a method and apparatus for extracting a signal out of noise and ascertaining its type. More particularly, the invention relates to a method for concurrently detecting a signal envelope and counting a predetermined number of zero access crossings in order to conclude that a signal is present. Discrimination among signal types may be executed by any one of a number of conventional means. The application for the method and apparatus is in the environment of automatic ringback signal detection for an automatic dialing system. This ringback signal is detected when the circuit is enabled after an automatic dial operation. Other signals which may occur at that time, such as a busy signal, noise, voice, or dial tone, are accurately rejected.

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Automatic Ringback Detector

This invention relates to a method and apparatus for extracting a signal out of noise and ascertaining its type. More particularly, the invention relates to a method for concurrently detecting a signal envelope and counting a predetermined number of zero access crossings in order to conclude that a signal is present. Discrimination among signal types may be executed by any one of a number of conventional means. The application for the method and apparatus is in the environment of automatic ringback signal detection for an automatic dialing system. This ringback signal is detected when the circuit is enabled after an automatic dial operation. Other signals which may occur at that time, such as a busy signal, noise, voice, or dial tone, are accurately rejected. The ringback signal consists of a tone with cyclic ON/OFF characteristics as follows: 0.4 seconds < tON < 2.5 seconds 3.5 seconds < tOFF < 4.0 seconds Furthermore, the frequency range for the tone is from 350-600 Hz. This ringback signal detector discriminates the presence of a signal that follows the above ON/OFF characteristics, and it also detects the tone's frequency in the specified range. Occurrence of both conditions asserts the existence of a ringback signal. In the figure, there is shown a block diagram of the circuit. The AGC normalizes the input signal providing a uniform peak-to-peak voltage of 1.2 volts for all input signals in the range from 0.020-6.0 volts. The band...