Electronic two-wire four-wire conversion circuit, in particular for subscriber telephone sets.

摘要

The invention relates to an electronic two-wire four-wire conversion circuit, in particular for subscriber telephone sets. This circuit includes, between the microphone M and the two-impedance wire subscriber line ZL, two identical common-base transistor stages T1 and T2 in series. A capacitor C is branched onto the second stage and a differential amplifier AD is connected to the terminals of the first stage and supplies the ear piece E. In the microphone -> line direction, the capacitor C has virtually no effect and the supplying of the line with current makes it possible to overcome its impedance. In the line -> earpiece direction, the impedance of the two stages is very high and the capacitor C makes it possible to transmit a voltage towards the point A without any alternating voltage transmitted towards the point B. The invention applies to electronic circuits for telephone sets. <IMAGE>