| 摘要 |
A switching device for a channel comprising a pair of lines, which comprises: (1) a voltage detector (8) that produces an output voltage in response to a voltage between the lines above a predetermined level; (2) a switch (9) that can change an impedance in one of the lines in response to an input voltage thereto; characterized in that: (a) the device additionally comprises a first storage device (2) that produces said input voltage, said input voltage being produced when the storage device reaches a charge V2, said storage device being initially at a voltage V1 that is less than V2 and after charging by the output voltage being at a voltage V3 that is greater than V2, said storage device discharging from V3 to V1 in the absence of the output voltage; and (b) the voltage detector (1) comprises a low-pass filter (R1, C1, D3, R2) such that an AC signal on the channel produces an output voltage that charges the first storage device to a charge below V2.
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