The present invention relates to a subscriber line interface circuit (hereinafter simply called SLIC), and more particularly to an improved circuit for providing a subscriber line or a trunk with direct current of a telephone switching circuitry.
A conventional SLIC is described in detail in an article by Denis W. Aull et al., entitled "A High-Voltage IC for a Transformerless Trunk and Subscriber Line Interface", IEEE Journal of Solid-State Circuits, volume SC-16, number 4, at pages 261-266, August 1981.
The above mentioned conventional circuit is composed of a differential signal detecting circuit, a common-mode potential detecting circuit and a differential current driving circuit, each of which includes operational amplifiers.