| 摘要 |
PURPOSE:To attain a monolithic control circuit and to facilitate easy miniaturization of a communication equipment by transmitting only a current showing the signal value through an impedance element for reception to perform reception and making use of the change of the inter-line voltage accordant with a transmission signal to perform transmission. CONSTITUTION:A current IC flowing to a resistor RC serving as an impedance element for reception is defined as IC = (inter-line voltage VL - load side voltage VC)/RC. Therefore, a current IS=IL-IC is satisfied by controlling the impedances of variable impedance element Z1 and Z2 so that both the VL and VC are fixed and the controlling a current I1. In other words, the current IS flowing to a resistor RS is equal to a signal component of 0-16mA in case a line current IL is set at 4-20mA, for example, by setting the current IC at a level equal to a bias component. Thus the reception value can be detected by the voltage VS. While the current IC is kept constant according to a transmission signal when the measured value, etc. sent to a controller. At the same time, both control voltages Vd1 and Vd2 are changed at a time. Therefore the VL is changed for execution of transmission. |
