| 摘要 |
PURPOSE:To simplify a circuit without using a special circuit for the side tone circuit, by connecting one terminal of a side tone input resistance to the incoming side of the input resistance of the transmitting operational amplifier of an operator talking circuit, and the other side to the incoming side of a receiving operational amplifier. CONSTITUTION:In the operator talking circuit of the manual desk which makes a call by using switching handset Hp, the transmitter circuit and receiver circuit are equipped with transmitting operational amplifier TAMP provided with input resistance Rit and feedback resistance Rfr, and receiving operational amplifier RAMP provided with input resistance Rir and feedback resistance Rfr. Then, one terminal of side tone input resistance Ris is connected to one-side terminals of input resistances Rit and Rir of both operational amplifiers TAMP and RAMP respectively. Connecting this side tone input resistance Ris makes it possible to maintain transmission and reception levels without providing a special attenuator or hydrid circuit. |
