| 摘要 |
A controllable resonant circuit e.g. for an RFID or a tag reader, comprises an inductor L1 and capacitors C1, C2, C3. A stimulus square wave generates an oscillation in the resonant circuit. A non-linear element FET1 is able to change the amount of capacitance according to whether it is conducting or not. The switching point of FET1 is controlled by its gate voltage, such that the resonant frequency changes according to the mark/space ratio of the oscillation. The change in resonant frequency also affects the amplitude of the relevant portions of the oscillation, such that the overall amplitude of the oscillation is thus controlled by the mark/space ratio. The tag may be an implanted tag for a cat, and detection of the tag by the reader leads to operation of a cat flap. |
