| 摘要 |
PROBLEM TO BE SOLVED: To solve the problem of not meeting the field bus standards due to the fact that impedance on the primary side of a pulse transformer lowers owing to the effect of a capacitor constituting a filter in the case of non- transmission. SOLUTION: In constitution in which an output from a three-state buffer is input to the secondary side of the pulse transformer through the filter with a capacitor and a transmission signal is extracted from the primary side of the pulse transformer, a diode is inserted between the filter and the pulse transformer, and the output from the three-state buffer is brought to high impedance in the case of non-transmission. Since the capacitor constituting the filter is detached substantially from the pulse transformer in the case of non- transmission, impedance on the primary side does not lower, and the standard of the field bus can be satisfied.
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