Browse Prior Art Database

Analog Conference Bridge

IP.com Disclosure Number: IPCOM000060965D
Original Publication Date: 1986-Jun-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 3 page(s) / 49K

Publishing Venue

IBM

Related People

Andrade, RJ: AUTHOR [+4]

Abstract

This article describes a conference circuit of relatively simple configuration with moderate capacity and minimum interface in an integrated communication network. Traditional problems encountered in analog conference circuits, such as instability, loss and impedance mismatching, have been minimized by the circuit disclosed herein. The summing algorithm used in this conference bridge sums the information of all participating channels into a composite signal. This total response is then transmitted to all the participants with the contribution from each participant subtracted from the composite sum of each participant's own phone.

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Analog Conference Bridge

This article describes a conference circuit of relatively simple configuration with moderate capacity and minimum interface in an integrated communication network. Traditional problems encountered in analog conference circuits, such as instability, loss and impedance mismatching, have been minimized by the circuit disclosed herein. The summing algorithm used in this conference bridge sums the information of all participating channels into a composite signal. This total response is then transmitted to all the participants with the contribution from each participant subtracted from the composite sum of each participant's own phone. In addition, while the composite information is the sum of the responses received from all participants, the output magnitude is carefully controlled by reducing the summing gain, as well as reducing the added background noise from all channels. This is due to 180-degree shift sampling of every other participant within each conference group. This circuit is used to receive signals from eight separate devices and allows, under computer control, the mixing of the audio signals. Each conference bridge is connected to the PABX switch just as the subscriber line interface circuit (SLIC) card in a PABX switch is connected and can handle eight conversations. Two conference bridge cards tied together will provide the designed maximum of sixteen conversations. Referring to Fig. 1, each bridge's eight inputs are divided into two groups of four, making two separate groups (A, B) or four separate groups (A, B, C and D) when the two conference bridge cards are combined. No more than one conference can take place in one of these individual groups at the same time. This restriction allows this conference bridge to be smaller and much less expensive than a fully non- blocking, sixteen port, conference bridge. Though an individual group is dedicated to a single conference, each group may be combined with any other group to form a wide variety of simultaneous conferences. The different conferences that are possible at the same time are indicated below, using two conference bridge cards together. 1. 13 to 16 participants or 2. 9 to 12 and 2 to 4 participants or 3. 5 to 8 and 5 to 8 participants or 4. 5 to 8 and 2 to 4 and 2 to 4 participants or 5. 2 to 4 and 2 to 4 and 2 to 4 and 2 to 4 participants This conference bridge can be packaged on a single integrated circuit card and can be used in intelligent PABX switching systems. It operates over a bandwidth of approximately 300 Hz to 3 KHz and can be used for mixing voice or tone energy. Referring to Fig. 1, the conference bridge contains eight receive signal conditioning circuits 1, eight signal control path and mixing circuits 2, eight transmit mixing sections 3, eight transmit signal and conditioning circuits 4, a crystal controlled programmable clock circuit 5, and computer control I/O circuits
6. The receive section passes incoming signals throug...