| 摘要 |
PURPOSE:To prevent the difference of common voltage from advancing in a transmission line and generating reflected wave when transmission is resumed by making common voltage at idle-time equal to that at the time of packet transmission. CONSTITUTION:When it is so arranged that on entering idle time, input signals D, -D stop H, L change and become D=H, -D=L, Q1 becomes on, base voltage of Q4 becomes low, and Q4 becomes off. Consequently, a condenser C is charged, and voltage between terminals rises slowly, and potential at point A drops. With a transistor Q8 continuously turned on, current flows through a passage of resistors R4, R5, diodes D2, D3, transistors Q8, Q9, and a resistor R6. As the values of resistors R4, R5 are equal to each other, voltages applied to the bases of transistors Q10, Q11 become equal. Accordingly, voltages applied to transmission lines X, -X are equal, and become an intermediate value between H, L levels. That is, constant current sources Q9, R6 are still effective and it only means that the current of the constant current source flowing near to H- side of input flows uniformly, and becomes an intermediate level between H, L levels.
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