| 摘要 |
In generating a ringing signal of predetermined frequency and shape between the A- and B-wires (LA, LB) to a subscriber's station (ZL) in a telephone network, the ringing signal is directly injected in or superposed on the DC-levels of the wires. A voltage difference converting means (1) converts any voltage difference between the A- and B-wires (LA, LB) into a first current (I1). A signal generating means (2) generates a first voltage of the frequency and shape of the ringing signal to be generated, and a signal converting means (3) then converts the first voltage into a second current (I2). In a summation node (4) the first current (I1) is subtracted from the second current (I2) to obtain a third current (I3), and this current is converted by passing it through a resistor (R1) to a second voltage. The second voltage is buffered (5) and is again converted to a fourth current (IR) by applying the voltage to resistor (RDC). This fourth current (IR) is amplified by current amplifiers circuits comprising operational amplifiers (6, 7), and is then supplied to the A-wire (LA) and drawn from the B-wire (LB). |
