Browse Prior Art Database

Subscriber Line Interface Circuit

IP.com Disclosure Number: IPCOM000039454D
Original Publication Date: 1987-Jun-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 45K

Publishing Venue

IBM

Related People

Wilkie, BJ: AUTHOR

Abstract

The figure illustrates the subscriber line interface (SLIC) which has the function of providing power to a variety of types of telephone sets without regard for their voltage requirements, and while minimizing the amount of injected noise from the power supplying the SLIC circuit. Conventional telephone handsets include a microphone which has a carbon canister filled with granules of carbon. In the conventional mode of operation, the carbon canister has a DC voltage applied across two plates, and the energy supplied by a spoken voice signal mechanically oscillates the granules so as to change the effective resistivity of the canister between the electrical plates. In order to make the carbon canister-type microphone work, a source of DC current must be supplied.

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Subscriber Line Interface Circuit

The figure illustrates the subscriber line interface (SLIC) which has the function of providing power to a variety of types of telephone sets without regard for their voltage requirements, and while minimizing the amount of injected noise from the power supplying the SLIC circuit. Conventional telephone handsets include a microphone which has a carbon canister filled with granules of carbon. In the conventional mode of operation, the carbon canister has a DC voltage applied across two plates, and the energy supplied by a spoken voice signal mechanically oscillates the granules so as to change the effective resistivity of the canister between the electrical plates. In order to make the carbon canister- type microphone work, a source of DC current must be supplied. Typically, when the telephone is connected to a telephone company circuit, power is supplied by what is archaically called a "talk battery." However, when a telephone set is to be connected to a micro-PABX, such as is the application for the invention disclosed herein, such "talk battery" power must be artificially supplied to the telephone set. A complicating feature is that the spoken signal, once converted into an electrical signal, must be conducted over the same wire into the circuit which also supplies the talk battery power. The circuit must be capable of stripping off the electrical analog signal so that it can be transmitted as is desired, while also providing the talk battery power to the microphone in the handset, that power having a minimum ripple noise distortion. As can be seen in the figure, the phone line interface 70 is connected to the telephone handset. Line 68 input and output to the phone line interface 70 carries both received and transmitted signals to and from the telephone handset. Line 68 must also carry the talk battery power necessary to power the microphone in the handset. An additional complication when adapting the SLIC circuit to a variety of telephones, is that there are some telephones currently in existence which are all electronic not having a carbon canister, but which do require the talk battery power in order to power the electronics within the telephone itself. Thus, it...