PURPOSE: To facilitate an integrated circuit implement by constituting a feeding circuit for a subscriber circuit of only an electronic part.
CONSTITUTION: When the input/output transfer coefficient of a current mirror circuit CM0 is denoted as an N, a current N.IDC flows to the output side of the CM0. Therefore, a current ILB=N.Rb/Reb flows through a line B by the current amplification of an operational amplifier Ab. On the other hand, a current (1+N)IDC flows to the reference side of the CM0, so a current ILA=N.IDC.Rb/ Rea flows to the side of a line A. Then, when Rea=Reb, ILA=ILB is obtained to supply a DC current to a subscriber terminal. Further, an unbalanced signal Vs from a four-wire side is converted by a voltage converting circuit TRN into a current i0, which is inputted to the CM0. The CM0 drives two operational amplifiers Aa and Ab to send a balanced signal between the lines A and B, thus performing balance/unbalance conversion.
UEHARA HIROYASU
HAYASHI TOSHIO
NIPPON TELEGRAPH & TELEPHONE