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Abstract

A technique for improving the radio frequency coupling between an external programming device and a medical device implanted within a patient. The radio frequency coupling is typically used to non-invasively change the operating parameters of the implanted device, such as a cardiac pacer. A common frequency for transmission is 175 khz. At this frequency, in view of the low power and the short distances involved, positioning of the external antenna with respect to the implanted antenna becomes critical. This criticality is heightened because of the great change in transmitter antenna loading and tuning with small changes in relative position. To assist the attending medical personnel, the transmitter antenna is ordinarily mounted within a paddle-like structure. A feedback coil is placed within the same physical package. The signal induced within the feedback coil is amplified, filtered, and integrated to produce a signal which controls the output amplifier of the transmitter. In this manner, a constant output field strength is provided, even though slight changes in physical position modifies output loading.

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First Claim