High speed digital telemetry system for implantable device

Implantable transmitter apparatus for transmitting digital binary data at a prescribed bit rate from an implantable device, said digital binary data comprising an input sequence of data bits, said transmitter comprising:

• encoding means for converting said input sequence of data bits into an encoded binary data stream, comprising a sequence of encoded incoming data bits, that includes an identifying mark only when a prescribed correlation exits between prescribed ones of said incoming data bits and encoded data bits;
• modulator means for modulating a carrier signal at said prescribed bit rate with said encoded binary data stream;
• a transmitting coil circuit tuned to said prescribed bit rate, said transmitting coil circuit including an inductor, a capacitor, and a switching circuit selectively connecting said capacitor to said inductor, a first and second side of said capacitor being connected to a first and second side, respectively, of said inductor in accordance with a first connection scheme of said switching circuit, and the first and second side of said capacitor being connected to the second and first side, respectively, of said inductor in accordance with a second connection scheme of said switching circuit, the first and second connection schemes of said switching circuit being defined in response to said identifying marks in said encoded binary data stream;
• and
• means for applying said modulated carrier signal to said transmitting coil circuit.

A telemetry system for transferring binary digital data between an implantable device and an external device comprising:

• a transmitter including
• encoding means for generating an encoded data stream from an input data stream of binary bits to be transferred, said encoded data stream being encoded using a bit coding scheme that places appropriate marks in the encoded data stream only when a prescribed correlation exists between prescribed data bits of said input data stream and said encoded data stream;
• modulation means for modulating a carrier signal having a frequency f.sub.0 with said encoded data stream,
• means for applying said modulated carrier signal to a transmitting coil;
• and
• a receiver including
• a receiving coil inductively coupled to said transmitting coil,
• a bandpass filter coupled to said receiving coil, said bandpass filter having a bandwidth of less than f.sub.0 Hz that is centered at approximately f.sub.0 Hz,
• a detector coupled to the output of said bandpass filter, and
• means coupled to the output of said detector to recreate therefrom said data stream;
• one of said transmitter or receiver being in said implantable device and the other being in said external device.

A method of transferring a sequence of data bits to and from an implantable device at a prescribed bit rate comprising:

• (a) generating an encoded binary data stream that includes an identifiable mark therein only when a prescribed correlation exists between prescribed ones of the data bits within said sequence of data bits to be transferred and prior encoded data bits within the encoded binary data stream;
• (b) modulating a carrier signal with said encoded binary data stream;
• (c) applying said modulated carrier signal to a transmitting coil;
• (d) selectively connecting a capacitor in parallel with said transmitting coil in response to the transitions of said encoded binary data stream in one direction, and reversing the connection of said capacitor to said coil in response to the transitions of said encoded binary data stream in the other direction;
• (e) inductively coupling a receiving coil to said transmitting coil, one of said transmitting coil or receiving coil being in the implantable device and the other being in an external device;
• (f) detecting the amplitude of only those components of the signal induced at the receiving coil having a frequency close to said prescribed bit rate;
• and
• (g) using the amplitude detected in step (f) to define the data that has been received.