Multichannel implantable cochlear stimulator

• US 5,776,172 A
• Filed: 05/25/1995
• Issued: 07/07/1998
• Est. Priority Date: 09/22/1989
• Status: Expired due to Term

• Current Assignee: Alfred E. Mann Foundation For Scientific Research
• Original Assignee: Alfred E. Mann Foundation For Scientific Research
• Inventors: Schulman, Joseph H., Gord, John C., Wolfe, James H., Strojnik, Primoz, Whitmoyer, David I.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): LAYNO, CARL HERNANDZ
• Application Number:
  US08/450,041
• Time in Patent Office: 1,139 Days
• Field of Search: 607/55-57, 607/60
• US Class Current: 607/56
• CPC Class Codes: A61N 1/36038 Cochlear stimulation
• CPC Class Codes: A61N 1/36185 Selection of the electrode configuration
• CPC Class Codes: A61N 1/37252 Details of algorithms or data aspects of communication system, e.g. handshaking, transmitting specific data or segmenting data
• CPC Class Codes: H04R 2460/03 Aspects of the reduction of energy consumption in hearing devices
• CPC Class Codes: H04R 25/505 using digital signal processing

Abstract

An implantable cochlear stimulator (ICS) has eight output stages (212), each having a current source (212B) connected to a pair of electrodes, designated "A" and "B", through respective output coupling capacitors and an electrode switching matrix (212C). An indifferent electrode is connected to each output stage by way of an indifferent electrode switch (212D). The current source generates a precise stimulation current as a function of an analog control voltage. The analog control voltage, in turn, is generated by a logarithmic D/A converter. The D/A converter serially converts data words, received in a data frame from an external source, to respective analog control voltages that are applied sequentially to the current sources of each output stage. An output mode register (208) controls the switching matrix of each stage, as well as the indifferent electrode switch, to configure the electrodes for a desired stimulation configuration, e.g., bipolar stimulation (current flow between the pair of electrodes of the output stage), or monopolar stimulation (current flow between one of the electrodes of the output stage and the indifferent electrode). The voltage at the "A" and "B" electrode of each output stage may be selectively telemetered to the wearable system, as may the current flow through the indifferent electrode, thereby facilitating a measurement of the electrode impedance. The "A" and "B" electrodes of each output stage may be selectively shorted through a high or low resistance in order to discharge the output coupling capacitors.

Claims

1. A implantable cochlear stimulator (ICS) for use with an external wearable processor (WP) system, said ICS comprising:

receiver means for receiving a data signal from the WP, the data signal comprising a series of data frames containing an end of frame signal, each data frame comprising a plurality of data words, each data word defining an amplitude for an output stimulation current for a different output channel of the ICS, and a command word for controlling a processor means in the ICS;

power supply means coupled to said receiver means for extracting a raw power signal from the data signal that powers the ICS;

a multiplicity of output stages, one for each of a multiplicity of output channels provided by said ICS, with each output stage having at least one stimulating electrode connected thereto;

processor means for serially processing the plurality of data words and command word in each data frame received by the receiver means and including

data word latching means for successively storing the data words,

logarithmic D/A converter means for converting the data word stored by the data word latching means to an analog signal voltage representative of the amplitude for the output stimulation current defined by the data word stored by the data word latching means,

switch means for coupling the analog signal voltage produced by the logarithmic D/A converter means to successive ones of the multiplicity of output stages; and

wherein

each of the multiplicity of output stages comprises;

refresh voltage controller means for generating an isolated refresh voltage for the output channel,

a voltage controlled current source powered by the isolated refresh voltage controller means for amplitude controlling, in accordance with the analog signal voltage coupled from the switch means, an output stimulation current, and

means for coupling the output stimulation current to the at least one stimulating electrode of the output stage.

2. The multichannel ICS of claim 1 wherein the ICS further includes telemetry means for transmitting a backtelemetry signal to the WP, said telemetry means comprising:

carrier means for generating a telemetry carrier signal,

decoder means coupled to the command detector means for generating a multiplexer control signal as a function of information received within the command word of the data frame,

multiplexer means for selecting one of a plurality of ICS status signals as a function of the multiplexer control signal,

modulator means for modulating the telemetry carrier signal with the ICS status signal selected by the telemetry multiplexer means;

whereby ICS status information may be selectively telemetered back to the WP.

3. The multichannel ICS of claim 2 wherein the refresh voltage controller means includes

voltage generation means for generating one of a plurality of isolated refresh voltages for use as a power source by the voltage controlled current source of each output stage, and

selection means for selecting one of the plurality of isolated refresh voltages as the power source to be used by the current source of each output stage, and wherein

the plurality of ICS status signals that may be telemetered back to the WP includes an indication of the power required for operation of the current source of each output channel, and wherein

the WP includes means for responding to the indication of the power required for operation of each output channel by sending a command word to the ICS that controls the selection means to select whichever one of the plurality of isolated refresh voltages minimizes power dissipation in the current source of each output stage,

whereby power dissipation in each output stage is reduced.

4. The multichannel ICS of claim 3 wherein the plurality of isolated refresh voltages generated by the voltage generation means comprises at least four, and wherein the highest of the at least four refresh voltages is selected as the power source to be used by the current source of each output stage in the absence of a command word from the WP that selects a lower isolated refresh voltage.

5. The multichannel ICS of claim 1 further including an indifferent electrode, and indifferent electrode switch means for selectively pairing the indifferent electrode with the at least one electrode of a specified output stage, and wherein said indifferent electrode switch means includes means for inserting a first resistor in series with the indifferent electrode, and wherein the plurality of ICS status signals includes a first voltage developed across said first resistor, which first voltage provides an indication of the stimulating current flowing through the indifferent electrode, whereby the ICS status information telemetered back to the WP may include an output voltage and a stimulating current for an electrode configuration that includes said indifferent electrode, from which ICS status information a determination of electrode impedance may be calculated.

6. The multichannel ICS of claim 5 wherein the indifferent electrode switch means further includes means for inserting a second resistor, having a resistance higher than the first resistance, in series with the indifferent electrode, whereby stimulating currents of a low amplitude may be more readily determined.

7. The multichannel ICS of claim 1 wherein the at least one stimulating electrode of each output stage is connected to its respective output stage through an output coupling capacitor, and wherein each output stage includes shorting means for selectively shorting the at least one stimulating electrode through a resistor in order to discharge the output coupling capacitor.

8. The multichannel ICS of claim 7 wherein the shorting means of each output stage includes means for selectively shorting its at least one stimulating electrode through a selected one of either a high resistance or a low resistance in order to control the discharge time of the output coupling capacitor.

9. The multichannel ICS of claim 1 wherein the output stage of each channel includes means for responding to a ZERO command, corresponding to a zero amplitude data word of a prescribed polarity in the data frame received from the WP, in a way that places the output stage in an open state, such that the at least one electrode of that output stage electrically floats.

10. The multichannel ICS of claim 1 wherein said power supply means includes means for converting said raw power signal into a plurality of different output voltages that power the ICS;

and wherein said refresh voltage controller means of each of the multiplicity of output stages comprises

a flying capacitor,

a refresh voltage source capacitor, and

refresh means for alternately connecting the flying capacitor to a selected one of the plurality of different output voltages and to the refresh voltage source capacitor during a refresh cycle so that the flying capacitor is connected to the selected output voltage and disconnected from the refresh voltage source capacitor during a first portion of the refresh cycle, and is disconnected from the selected output voltage and connected to the refresh voltage source capacitor during a second portion of the refresh cycle, and wherein the voltage on the refresh voltage source capacitor comprises the isolated refresh voltage generated by the refresh voltage controller means;

whereby the flying capacitor of each of said multiplicity of output channels, being alternately connected to the selected power supply voltage and to the refresh voltage source capacitor, provides electrical isolation of the refresh voltage for that output channel.

11. The multichannel ICS of claim 10 wherein the refresh means repeats the refresh cycle at a rate of at least 137.5 KHz.

12. The multichannel ICS of claim 10 wherein the receiver means includes means for receiving a Manchester encoded data stream comprising an amplitude-modulated RF signal consisting of a serial sequence of a prescribed number of bits representing m words of n bits each, where m and n are integers, and means for deriving a clock signal from such Manchester encoded data stream, said clock signal being used by said refresh means to define said refresh cycle.

13. The multichannel ICS of claim 12 wherein said means for deriving a clock signal from the Manchester encoded data stream comprises phase-lock loop means for locking to the pulse edges of the Manchester encoded data stream and deriving a data clock signal having a rate twice that of the Manchester encoded data rate.

14. The multichannel ICS of claim 13 wherein the means for deriving the clock signal from the Manchester encoded data stream comprises means for dividing the data clock signal by a prescribed integer factor.

15. The multichannel ICS of claim 13 wherein the Manchester encoded data rate comprises 550 KHz, and wherein the rate of the data clock signal comprises 1.1 MHz.

16. The multichannel ICS of claim 12 wherein m and n each are equal to nine.

17. The multichannel ICS of claim 12 wherein the Manchester encoded data stream further includes a parity bit and an end-of-frame marker bit following the m words of n bits each.

18. A multichannel implantable cochlear stimulator ICS) comprising:

(a) receiver means for receiving a data signal from an external transmitter, the data signal comprising a series of data frames separated by a parity bit signal and an end of frame signal, each data frame comprising a plurality of data words, each data word defining an amplitude for a tissue stimulating signal for a different output channel of the tissue stimulator, and a command word for controlling a processor means in the tissue stimulator;

(b) power supply means coupled to said receiver means for extracting a raw power signal from the data signal, said raw power signal being used to provide operating power for the human tissue stimulator;

(c) a plurality of output channels, each having an electrode connected thereto;

(d) processor means for serially processing the plurality of data words and command word in each data frame received by the receiver means and including

a command detector responsive to the command words for controlling the functions of the processor,

data word latching means for successively storing the data words,

logarithmic D/A converter means for converting the data word stored by the data word latching means to an analog control voltage, and

switch means for successively coupling the analog control voltage to successive ones of the output channels; and

(e) current source means within each of said output channels for generating a stimulation current having a magnitude controlled by said analog control voltage received through said switch means, and applying said stimulation current to the electrode of said output channel.

19. The multichannel ICS of claim 18 further including

(f) means for generating a plurality of ICS status signals, and

(g) back telemetry means for generating a back telemetry signal, receivable by an external receiver, that contains a selected ICS status signal.

20. The multichannel ICS of claim 19 wherein said ICS further includes data conditioner means for generating a carrier detect signal whenever said data signal is being received, said carrier detect signal comprising one of said plurality of ICS status signals.

21. The multichannel ICS of claim 19 wherein said ICS further includes clock decoder means for generating a clock signal and a phase locked loop (PLL) lock signal, the PLL lock signal being generated only when the generated clock signal is phase-locked to the data signal, said PLL lock signal comprising one of said plurality of ICS status signals.

22. The multichannel ICS of claim 19 wherein said ICS further includes parity error detection means for generating a parity alarm signal whenever a parity error occurs within the data frame, said parity alarm signal comprising one of said plurality of ICS status signals.

23. The multichannel ICS of claim 19 wherein said power supply means comprises voltage downconverter means for generating a plurality of different operating voltages from the raw power signal, and power bad detector means for generating a power bad signal whenever at least one of the operating voltages is less than a prescribed reference voltage, said power bad signal comprising one of said plurality of ICS status signals.

24. The multichannel ICS of claim 19 wherein said back-telemetry means includes means for generating a back-telemetry carrier signal, means for modulating said back-telemetry carrier signal with a selected one of said ICS status signals, and means for preventing the generation of said back-telemetry carrier signal when a prescribed combination of said ICS status signals exists.

25. A multichannel implantable cochlear stimulator (ICS) for use with an external wearable processor (WP) comprising:

a multiplicity of output stages, one for each of a multiplicity of output channels provided by said ICS, with each output stage having an "A" and a "B" stimulating electrode connected thereto through an output coupling capacitor;

shorting means for selectively shorting the "A" and "B" electrodes of each output stage through a resistor in order to discharge the output coupling capacitor, said shorting means shorting the "A" and "B" electrodes through a selected one of either a high resistance of at least 150K ohms or a low resistance in order to control the discharge time of the output coupling capacitor;

an indifferent electrode;

indifferent electrode switch means for connecting the indifferent electrode to each output stage;

processor means for controlling the functions of the ICS, including setting an electrode configuration in each output stage of the ICS;

current source means for generating a precise stimulation current pulse that is applied between a first electrode and a second electrode of said ICS, said first and second electrodes belonging to a group of electrodes that comprises the "A" and "B" electrodes of each of said multiplicity of output stages and said indifferent electrode;

electronic switching matrix means included within each of said multiplicity of output stages, and responsive to control signals generated by the processor means, for configuring the "A" and "B" electrodes of each output stage and the indifferent electrode in a prescribed electrode configuration; and

receiver means for receiving a data signal from the WP, the data signal defining a first specified electrode and a second specified electrode of said ICS, and the data signal further defining the magnitude of the precise stimulation current pulse.

26. The multichannel ICS of claim 25 wherein said receiver means includes means for receiving a data signal from the WP that comprises a series of data frames containing an end of frame signal, each data frame comprising a plurality of data words, each data word defining an amplitude for an output stimulation current for a different output channel of the ICS, and a command word for controlling the processor means of the ICS.

27. The multichannel ICS of claim 26 wherein said processor means further includes means for serially processing the plurality of data words and command word in each data frame and further including

data word latching means for successively storing the data words,

logarithmic D/A converter means for converting the data word stored by the data word latching means to an analog signal voltage representative of the amplitude for the output stimulation current defined by the data word stored by the data word latching means,

switch means for coupling the analog signal voltage produced by the logarithmic D/A converter means to successive ones of the multiplicity of output stages.

28. A multichannel implantable cochlear stimulator (ICS) for use with an external wearable processor (WP) comprising:

a multiplicity of output stages, one for each of a multiplicity of output channels provided by said ICS, with each output stage having an "A" and a "B" stimulating electrode connected thereto;

an indifferent electrode;

indifferent electrode switch means for connecting the indifferent electrode to each output stage, and including means for inserting a first resistor in series with the indifferent electrode;

processor means for controlling the functions of the ICS, including setting an electrode configuration in each output stage of the ICS;

current source means for generating a precise stimulation current pulse that is applied between a first electrode and a second electrode of said ICS, said first and second electrodes belonging to a group of electrodes that comprises the "A" and "B" electrodes of each of said multiplicity of output stages and said indifferent electrode;

electronic switching matrix means included within each of said multiplicity of output stages, and responsive to control signals generated by the processor means, for configuring the "A" and "B" electrodes of each output stage and the indifferent electrode in a prescribed electrode configuration; and

telemetry means for transmitting a backtelemetry signal to the WP, said telemetry means comprising carrier means for generating a telemetry carrier signal, means for generating a multiplexer control signal, means for generating a plurality of ICS status signals, multiplexer means for selecting one of the plurality of ICS status signals as a function of the multiplexer control signal, and modulator means for modulating the telemetry carrier signal with the ICS status signal selected by the telemetry multiplexer means, and wherein said ICS status signals include output voltages at the "A" and "B" electrodes of each output stage, and a first voltage developed across said first resistor, which first voltage thereby provides an indication of the stimulating current flowing through the indifferent electrode, whereby selected ICS status information is telemetered back to the WP via the backtelemetry signal.

29. A multichannel implantable human tissue stimulator comprising:

(a) receiver means for receiving a data signal from an external transmitter, the data signal comprising a series of data frames, each data frame including a plurality of data words wherein each data word defines an amplitude for a tissue stimulating signal for a different output channel of the tissue stimulator;

(b) power supply means coupled to said receiver means for extracting a raw power signal from the data signal, said raw power signal being used to provide operating power for the human tissue stimulator;

(c) a plurality of output channels, each having an electrode connected thereto, and each having a refresh voltage controller means therein for generating an isolated refresh voltage;

(d) processor means for processing the plurality of data words in each data frame received by the receiver means and including

data word latching means for storing the data words,

converter means for converting the data word stored by the data word latching means to an analog control voltage, and

switch means for coupling the analog control voltage to a selected one of the output channels; and

(e) current source means within each of said output channels for generating a stimulation current from said isolated refresh voltage having a magnitude controlled by said analog control voltage received through said switch means, and applying said stimulation current to the electrode of said output channel.