Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
2000-01-27
2001-11-20
Getzow, Scott M. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
Reexamination Certificate
active
06321118
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to implantable medical devices, and more particularly to a method and apparatus for detecting a power link between an external programmer/controller device and an implantable medical device.
In U.S. Pat. No. 5,569,307 there is disclosed an implantable cochlear stimulator (ICS) having back telemetry features. The back telemetry features allow an external wearable processor (WP), inductively linked with the ICS, to receive data and status signals from the ICS. These data and status signals assure that the WP is in proper signal contact with the ICS, and that the ICS is functioning properly. More particularly, as disclosed in the '307 patent, only when a prescribed combination of various status signals within the ICS are present, is a back-telemetry carrier signal and FSK data transmitted to the WP. The back-telemetry carrier signal, when received at the WP, thus acts as a handshake signal to signal the WP that the ICS is in proper signal communication with the WP, and that operation of the ICS can proceed. If the backtelemetry carrier signal is not received by the WP, then the WP does not send the necessary initialization data to the ICS, and operation of the ICS cannot proceed. The '307 patent is incorporated herein by reference.
Unfortunately, detection of the back-telemetry power signal requires appropriate detection circuitry within the external unit. While such detection circuitry may be of any straightforward design, it takes additional components and consumes additional power. Additional componentry and higher power consumption were not significant design considerations for a WP of the type disclosed in the '307 patent because the WP therein disclosed is a belt-worn or pocket-carried device powered with an easy-to-replace battery. However, such is not the case with the newer external units designed to be worn behind the ear. Rather, such behind-the-ear (BTE) units must be both physically small and light weight. Moreover, such BTE units, while ultimately designed, perhaps, for use with more-efficient implantable units, must be backwards compatible. That is, the small, light-weight BTE unit must still provide the operating power and control signals necessary to operate an existing ICS, including an ICS of the type described in the '307 patent. Hence, it is seen that there is a need for power-link detection circuitry within the BTE unit that is able to detect when a valid power link exists between the BTE and the ICS. Such power-link detection circuitry must be much smaller than, and must consume significantly less power than, the detection circuitry that would otherwise have to used to detect a back-telemetry carrier signal.
SUMMARY OF THE INVENTION
The present invention addresses the above and other needs by providing a dual directional coupler in the forward power-delivery path of an external transmitter adapted to transmit power to a receiver of an implantable medical device. The dual directional coupler monitors both the forward and reflected (or reverse) power being sent to, and being reflected from, the implantable device. When a valid power link has been established, the reflected power falls below a prescribed threshold. When a valid power link does not exist, or when a previously-established power link is broken, then the reflected power rises above the prescribed threshold. Thus, the present invention determines whether a valid power link exists by simply monitoring whether the reflected power is above or below the prescribed threshold. Should the reflected power be above the prescribed threshold, then that indicates a proper power link does not exist, or has been lost or broken, and a power link status signal is generated indicating a NO-LINK condition. A NO-LINK condition indicates that appropriate corrective action must be taken. Upon undertaking such corrective action, the reflected power will drop below the prescribed threshold, and the power link status signal will change to a LINK condition. A change from a NO-LINK to a LINK condition in the power link status signal automatically causes reinitializing the implant device by sending a new initialization sequence.
The invention may be characterized as an apparatus that determines whether a power link has been established with an implantable medical device. The apparatus includes: an RF oscillator that generates an RF signal; a headpiece having a transmitting coil; a power amplifier that amplifies the RF signal to produce an RF power signal; an output power path that connects the RF power signal with the transmitting coil; a directional coupler connected in-line with the output power path between the power amplifier and the transmitting coil, the directional coupler having a reflected power port on which a reflected power signal appears having a magnitude proportional to reflected power present on the output power path; and a comparator circuit that compares the reflected power signal to a threshold reference signal and that generates a power link status signal as a function of whether the reflected power signal exceeds the threshold reference signal; wherein the power link status signal provides an indication of whether a power link is established with the implantable medical device.
The present invention may further be characterized as a method of determining whether a power link is established with an implantable medical device. Such method includes the steps of: (a) generating a power signal; (b) transmitting the power signal to the implantable medical device over an output power path; (c) monitoring reflected power present on the output power path; (d) comparing the reflected power to a threshold reference signal; and (e) generating a power link status signal as a function of the comparison performed in step (d).
It is an object of the present invention to provide a method and apparatus for detecting when a valid power link condition exists between a transmitting circuit and a receiving circuit without the need for back-telemetry signals from the receiving circuit.
It is a further object of the invention to provide power-link detection circuitry that consumes very little power, e.g., much less than 1 mW, is very small, and is thus suitable for use in a small, light-weight, battery-operated BTE cochlea-stimulation systems.
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Advanced Bionics Corporation
Getzow Scott M.
Gold Bryant R.
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