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Cochlear implant utilizing multiple-resolution current sources and flexible data encoding

Cochlear implant utilizing multiple-resolution current sources and flexible data encoding description/claims

The present invention relates to an implanted auditory prosthesis that utilizes multiple-resolution current sources and a data encoding scheme.

Cochlear implants are electronic medical device to help deaf or severely-hearing-impaired people. They typically consist of an external signal processor, a transmission coil, an implantable package with a receiver coil, a hermetically sealed circuit, and an electrode array. More particularly, these systems include a microphone to receive sounds and convert them into corresponding electrical signals. These electrical signals may then be processed to generate a series of stimulation pulses that are delivered to the inner ear using a series of implanted electrodes. The stimulation of these implanted electrodes allows the implantee to perceive the corresponding ambient sounds.

A typical cochlear implant includes both an external component and an internal component. The external component will typically include a microphone, a speech processor, and a radio-frequency transmitter, while the internal component includes an implanted receiver, a hermetically-sealed decoding circuit, and a series of implanted electrodes. However, there are also numerous other designs currently available. Regardless of the specific configuration, a basic premise of all cochlear implant devices is that ambient sounds are detected by the microphone and a transduced signal representative of this signal is then generated. The transduced signal is then processed by a speech processor in accordance with one of several possible strategies.

One of the primary design considerations for cochlear implants is the current source design. To that end, there are two primary types of current source designs currently in use. The first is to use one current source for all N electrodes, while the second approach is to use N current sources for N electrodes. Some products even use 2N current sources for N electrodes for more flexibility. Each solution has its own advantages and disadvantages. For example, with one current source for all electrodes, the size, complexity, and power consumption of current stimulator are low. But the stimulation mode is also restricted by the ability of one current source. No simultaneous stimulation, current steering, or multi-polar stimulation strategies are supported. For N (or 2N) current sources for N electrodes, more flexibility and functionality of stimulation are achieved at the expense of size, complexity, and power consumption.

Current resolution is an important factor for current source design, especially for low stimulation level. For cochlear implant users, the ratio of current variation versus current Δl/I is more important than the current variation ΔI itself. Traditional linear step-size current source uses a constant ΔI. Therefore, at low stimulation level where I is small, ΔI/I is large. To lower ΔI/I, one solution is to increase the number of current amplitude bit. However, this results in an increase in the number of current sources in the internal circuit and lowers the stimulation rate (8-bit requires 256 unit current sources and 10-bit requires 1024 unit current sources). When the stimulation level is close to the most comfortable loudness (MCL) and the value I is large, ΔI/I is usually too small and the resolution space is wasted. As such, there is a need for an improved cochlear implant which provides a more balanced solution for both complexity and functionality.

Disclosed and claimed herein is a programmable cochlear implant that utilizes multiple current sources and a flexible data-encoding scheme. In one embodiment of the invention, a method for stimulating electrodes implanted in a human inner ear includes the acts of multiplexing current sources in accordance with a stimulation mode set using a command frame, and encoding stimulation data for the stimulation of the plurality of electrodes in a data frame following the command frame, where the stimulation data include electrode address information, phase polarity information and amplitude information. The method further includes generating a stimulation pulse based on the stimulation data and using one or more of the current sources in accordance with the stimulation mode, and delivering the stimulation pulse to the electrodes in accordance with the stimulation data.

Other aspects, features, and techniques of the invention will be apparent to one skilled in the relevant art in view of the following detailed description of the invention.

FIG. 1 is a block diagram of one embodiment of a cochlear prosthesis in which two current sources are utilized;

FIG. 2A is the data encoding format supporting from two current sources in accordance with one embodiment;

FIG. 2B is one embodiment of a scheme of self-timing with pulse-width-modulation bit coding;

FIG. 3 depicts stimulation modes supported by the data encoding scheme of one embodiment of the invention;

FIGS. 4A-4C depict embodiments of switch networks for various stimulation modes;

FIGS. 5A-5F depict embodiments of command and data frames for various stimulation modes in accordance with the principles of the invention;

FIGS. 6A-6B depict an arbitrary waveform generator according to one embodiment of the invention;

FIG. 7 illustrates one embodiment of a nonlinear step size current source implementation scheme;

FIG. 8 shows one embodiment of a schematic for a reference current selection and offset current control circuit; and

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