| 摘要 |
An electric device is intended for detecting the presence of a signal having a certain frequency (401) in a line connection (301). It comprises at least three energy-storing components (302, 303, 304, 305, 501, 502, 503, 504) connected in parallel to the line connection, switching means (306) for making a connection selectively from each energy-storing components to a certain reference, means (CLK1, CLK2) for controlling the switching means at a predetermined frequency, and means (307, 308, 309) for measuring a certain quantity comparable to the energy stored from each energy-storing component. |
