| 摘要 |
842,274. Sub-station circuits. SVENSKA RELAFABRIKEN A.B. Dec. 30, 1957 [Nov. 26, 1957], No. 40338/57. Class 40 (4). A loud-speaking telephone instrument comprises microphone and loud-speaker amplifiers powered by D.C. received over the incoming line suitably stabilized, and comprises control means for the amplifiers so arranged that a signal through one of the amplifiers increases the gain of that amplifier and decreases the gain of the other, the said decrease being greater than the said increase. As shown the microphone amplifier comprises transistors TS1, TS2, TS3 and TS4, TS5 in push-pull the output of the latter feeding the line via hybrid transformer T3. Incoming signals pass via transformer T3 and an amplifier comprising TS8, TS9 and TS10, TS11 in push-pull to loudspeaker H. The partially amplified microphone signal from TS2 also feeds the amplifier TS6, TS7 whose output feeds rectifiers D6, D10 via windings II and III of transformer T5, winding III having more turns than winding II. Rectifier D6 is also back-biased more than D10 so that it starts to charge its condenser C16 later than D10 starts to charge its condenser C27 so allowing the microphone amplifier to increase its gain only at a later time than the loud-speaker amplifier starts to decrease its gain. The voltage developed across C16 decreases the current flowing through diodes D1, D2 so increasing the shunt resistance across the input to TS2 so increasing the microphone amplifier gain. The voltage developed across C27 increases the current flowing through diodes D14, D15 so decreasing the shunt resistance across the input to T58 so decreasing the loud-speaker gain. An incoming signal after passing through the loudspeaker amplifier is further amplified by TS12 and rectified by D11, D12 which operate in a manner similar to D6, D10 to reduce the microphone amplifier gain and increase the loudspeaker amplifier gain. The latter gain is, however, subject to limitation effected by diode D13 which conducts when the output exceeds a predetermined value to decrease the shunt impedance of D14, D15 and so reduce the amplifier gain. D.C. from the incoming line is received via the right-hand windings of T3 and applied to bridge rectifier SVL whose output polarity is independent of the input polarity. The D.C. is then subject to stabilization by the shunt diodes D7 ... D8 prior to feeding the amplifiers. Semi-conductor diodes D3, D16 have negative temperature coefficients and afford voltage and temperature stabilization. Resistors R10, R32 have a negative temperature coefficient for effecting temperature stabilization of the amplifiers. A local power supply BA may be supplied. |
