PURPOSE: To expand the range where a non-distortion maximum output amplitude of a receiver is permitted to cover by energyzing a preamplifier and the 1st differential amplifier of the next stage from a smoothed power line on which no power voltage fluctuation of a talking line appears directly.
CONSTITUTION: An output of the preamplifier 2 including a receiving amplifier A2 is inputted to the 1st differential amplifier 3. Collectors of transistors (hereinafter called TRs) Q1, Q2 being components of the amplifier 3 are energized by smoothed power lines VCC1, VCC2. An output of the amplifier 3 is outputted to TRs Q4, Q5 of the 2nd amplifier 4 and collectors of the TRs Q4, Q5 are connected to a talking line L1'. The output of the amplifier 4 is outputted to TRs Q7, Q8 of the amplifier 5 and collectors of the TRs Q7, Q8 are connected to the line L1'. Thus, a transmission signal and a reception signal are superimposed between talking lines L1' and L2' and the circuit current is stabilized by a constant current circuit comprising TRs Q6, Q9 and Q10.
HISHINUMA ESAO
OSANAWA TATSUHIRO
NISHINO YUTAKA
NIPPON TELEGRAPH & TELEPHONE