| 摘要 |
An externally generated myriametric frequency magnetic carrier signal is resonantly reflected by a tuned coil in an implant. The lagging phase angle of the reflected signal is modulated at very low power by varying the impedance across the tuned coil in accordance with a data input signal. An external phase shift demodulator recovers the transmitted data. To assure adequate coupling between the external unit and the implant, the output level of an external phase comparator must exceed a given threshold to signify "acquisition" before data is transmitted from the implant. In a preferred embodiment, a shunt circuit across the tuned coil is opened and closed in accordance with a digital input signal generated by the implant. The external telemetry unit preferably includes a coaxially spaced triple coil assembly. The middle coil transmits the carrier. The outer pickup coils are balanced to minimize carrier reception. For two-way communication an IR transmitter is added to the coil assembly. During acquisition, the output of the tuned coil is used to turn on a dormant IR receiver in the implant. Light emitting diodes are preferably mounted in an array on the face of the coil assembly surrounded by an optional reed switch coil for multimode telemetry in the programmer.
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