| 摘要 |
PURPOSE:To reduce the mounting area by providing a filter function to the feeding circuit in a polarity inverting pulse transmission circuit to eliminate the need for an externally mounted charging filter. CONSTITUTION:When a control signal of feeding circuit OFF is inputted to an input terminal 35, transistors (TRs) 31, 29, 30 are turned off, then TRs 27, 28 are turned off and a voltage feedback loop is opened. Since a capacitor C26 is charged gradually to a voltage of a power supply 5 through resistors 16, 17, the bias of TRs 18, 19 is reduced gradually to zero and a talking current flowing to output terminals 24, 25 is reduced gradually to zero. Thus, the feeding circuit has a filter characteristic, the noise appearing between terminals 24, 25 is very small. When a control signal of feeding circuit ON is inputted to the terminal 35, Trs 31-27 are turned on, a voltage feedback loop is formed and the TRs 18, 19 are biased. Since the voltage of the C26 attains gradually to a collector voltage of the TRs 18, 19 through resistors 12, 13, the talking current is increased gradually and the noise appearing at the terminals 24, 25 is made small. |
