Daisy chainable sensors and stimulators for implantation in living tissue

An implantable medical device comprising:

• an hermetically sealed part containing electrical circuitry;
• said electrical circuitry performing a medical function selected from the group consisting of medical electrical stimulation, medical electrically mediated stimulation, medical electrical sensing, the combination medical electrical stimulation and electrical medical sensing, medical electrical-mediated release of medication at an implant site and medical electrical-mediated release of medication at a non-implant site;
• a non-hermetically sealed part, the non-hermetically sealed part including a first pair of terminals and a second pair of terminals, wherein the first pair of terminals are electrically connected to the second pair of terminals;
• and
• feed-through means for making electrical contact between each terminal of the first pair and second pair of terminals and a respective portion of the electrical circuitry within the hermetically sealed part;
• wherein said first pair of terminals comprises a means for applying electrical power and data to the electrical circuitry within the hermetically sealed part, as well as a means for receiving data from the electrical circuitry within the hermetically sealed part, and said second pair of terminals similarly comprises a means for passing the electrical power and data received on the first pair of terminals to a corresponding first pair of terminals of another implantable medical device, whereby a plurality of said implantable medical devices may be daisy-chained together by connecting a pair of conductors between the second pair of terminals of one implantable medical device and the first pair of terminals of another implantable medical device;
• said implantable medical device wherein the implantable medical device comprises an implantable sensor that senses a parameter associated with living tissue within which the medical device is implanted, and wherein the hermetically sealed part of the implantable medical device includes electronic sensor circuitry for operating and monitoring said sensor, and further wherein the electronic circuitry receives electrical signals through the faced-through means that power and control the operation of said sensor;
• said medical device wherein the implantable sensor generates an electrical current having a magnitude that varies as a function of the sensed parameter, and wherein the electronic sensor comprises
• a rectifier circuit connected to the first pair of terminals, said rectifier circuit including means for generating an operating voltage from an electrical signal applied across said first pair of terminals;
• a line interface circuit also connected to the first pair of terminals for detecting input data within the electrical signal applied across said first pair of terminals, and for allowing output data to be placed within the electrical signal appearing across said first and second pair of terminals;
• current-to-frequency converter means coupled to the sensor for converting the electrical current generated by the sensor to a signal comprising a stream of electrical pulses, wherein the time interval between adjacent pulses of said stream of electrical pulses varies as a function of the magnitude of the electrical current;
• and
• a counter circuit for counting the number of pulses that occur within the stream of electrical pulses within a set time period, the number of pulses thus counted providing a measure of the electrical current, the count derived by said counter circuit after said set time period comprising output data that is coupled to said line interface circuit.

A chain of serially-connected electronic devices adapted for implantation in living tissue comprising:

• a plurality of substantially identical electronic devices, each electronic device including a first pair of terminals, a second pair of terminals, means for receiving an input pulsed data-stream signal over the first pair of terminals, means for performing a medical function selected from the group consisting of medical electronic stimulation, medical electronically mediated stimulation, medical electronic sensing, the combination medical electronic stimulation and electronic medical sensing, medical electronic-mediated release of medication at an implant site and medical electronic-mediated release of medication at a non-implant site, and means for applying output pulses to the first pair of terminals representative of the specified function performed so that the output pulses are interleaved between pulses of the input pulsed data-stream signal;
• a control circuit having a first line terminal and a second line terminal, means for generating the input pulsed data-stream signal and applying said input pulsed data-stream signal between the first line terminal and the second line terminal, and means for detecting any output pulses appearing between pulses of the input pulsed data-stream;
• a first line conductor connected between the first line terminal of the control circuit and a first terminal of the first pair of terminals of a first electronic device, and a second line conductor connected between the second line terminal of the control circuit and a second terminal of the first pair of terminals of the first electronic device;
• and
• for each additional electronic device included in the chain of implantable serially-connected electronic devices, wherein an electronic device in the chain that is closest to the control circuit comprising a forward electronic device, and an electronic device in the chain that is next closest to the control circuit comprising a rearward electronic device
• a signal conductor connected between a first terminal of the second pair of terminals of the forward electronic device and a first terminal of the first pair of terminals of the rearward electronic device, and
• a return conductor connected between a second terminal of the second pair terminals of the forward electronic device and a second terminal of the first pair of terminals of the rearward electronic device;
• whereby the first electronic device is connected to the control circuit with just two conductors, and each rearward electronic device in the chain of electronic devices is also coupled to the forward electronic device with just two conductors;
• said chain of implantable electronic devices wherein the specified function performed by each of the plurality of electronic devices comprises sensing and measuring a parameter associated with the living tissue within which the chain of devices is implanted;
• said chain of implantable electronic devices wherein the input pulsed data stream signal generated by the control circuit comprises a train of biphasic pulses, with each biphasic pulse in the train of pulses comprising a negative pulse followed by a positive pulse to represent one binary state, and a positive pulse followed by a negative pulse to represent the other binary state, and wherein each biphasic pulse is separated from an adjacent biphasic pulse in the train of biphasic pulses by a time period T1, and further wherein the train of biphasic pulses is applied to the first pair of terminals of each electronic device in the chain.

A method of sending power and control data to, and receiving transmit data from, a plurality of implantable medical devices, each connected to a two-conductor cable, comprising:

• (a) generating a biphasic pulse train of biphasic pulses at a regular repetition rate of F1 pulses per second (pps), wherein each biphasic pulse in the pulse train has a width T.sub.W and is separated from an adjacent pulse in the pulse train by a time separation distance of T1, where T.sub.W is <<T1, and T1=1/F1;
• (b) modulating the pulses of the pulse train to represent data bits, wherein a biphasic pulse which goes positive first and then negative comprises a first binary state, e.g., a logical one, and wherein a biphasic pulse which goes negative first and then positive comprises a second binary state, e.g., a logical zero;
• (c) arranging the biphasic pulses of the pulse train in data frames of N data bits each, wherein a first subset of the N data bits comprise address bits, a second subset of the N data bits comprise an operational code, a third subset of the N data bits comprise data;
• (d) applying the data frames to the two-conductor cable so that the data frames are received by each of the plurality of implantable medical devices connected to the two-conductor cable;
• (e) receiving and processing the data frames within each medical device by:
• (1) splitting the received biphasic pulses into first and second signal paths,
• (2) rectifying and filtering the biphasic pulses received in the first signal path to create an operating voltage used to operate the medical device,
• (3) demodulating the address bits received in the second signal path of each data frame to determine if the address bits match a predetermined address stored in the medical device, and
• (4) if the address bits match the predetermined address, demodulating the operational code and data received in the second data path;
• and
• (f) sending transmitted data from a medical device for which a match exists between the address bits received and the predetermined address by:
• (1) generating an output data pulse having a width <<T1, the output data pulse having a first amplitude, e.g., a maximum amplitude, to represent a first binary state, and a second amplitude, e.g., a minimum amplitude, to represent a second binary state, and
• (2) applying the output data pulse to the two-conductor cable at a time in the data frame that is inbetween the biphasic pulses of the N data bits that define a data frame.