Electronic two-wire/four-wire conversion circuit with voltage/current feedback

摘要

The invention relates to an electronic two-wire/four-wire conversion circuit with voltage/current feedback, in particular for a subscriber telephone set. This circuit connects the microphone M to the subscriber line with impedence ZL via two common-base transistor stages with differing emitter resistance values R; R1, in series; thus the speech signals coming from the microphone are transmitted by a current drive of the line. The earpiece E provides the voltage difference between the input B of the circuit and the output A of the first stage in which the speech signals coming from the line are transmitted via a common-collector transistor stage T3, R, R2. The emitter resistances R; R1; R2 are related by a relation involving their ratio. The invention applies to electronic circuits for telephone sets. <IMAGE>