Surgery: light – thermal – and electrical application – Light – thermal – and electrical application – Electrical therapeutic systems
Reexamination Certificate
1999-06-23
2001-01-30
Kamm, William E. (Department: 3762)
Surgery: light, thermal, and electrical application
Light, thermal, and electrical application
Electrical therapeutic systems
C607S057000
Reexamination Certificate
active
06181969
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to implantable medical devices, and more particularly to the output stage of an implantable electrical stimulator. Even more particularly, the invention relates to a programmable output current source for use within an implantable tissue or nerve stimulator, e.g., an implantable cochlear stimulator.
In the implantable medical device field, a medical device, configured to perform a desired medical function, is implanted in the living tissue of a patient so that a desired function may be carried out as needed for the benefit of the patient. Numerous examples of implantable medical devices are known in the art, ranging, from implantable pacemakers, cochlear stimulators, spinal cord stimulators, muscle stimulators, glucose sensors, and the like.
Some implantable medical devices are configured to perform the stimulating function, i.e., to generate an electrical signal, typically a biphasic current pulse, that is applied to body tissue or to a nerve, for the purpose of causing a desired muscle contraction, or activating a desired nerve. Examples of medical devices that perform the stimulating function are shown, e.g., in U.S. Pat. Nos. 5,193,539 and 5,603,726, both of which patents are incorporated herein by reference. The present invention is directed to such implantable stimulating devices.
Other medical devices are configured to perform the sensing function, i.e., to sense a particular parameter, e.g., the amount of a specified substance in the blood or tissue of the patient, and to generate an electrical signal indicative of the quantity or concentration level of the substance sensed. An example of an implantable medical device that performs the sensing function is shown, e.g., in U.S. Pat. No. 4,671,288. Sometimes, sensing a desired parameter or other element, e.g., an evoked response, occurs through the same or similar electrodes through which stimulation is applied.
Some stimulating devices, e.g., cardiac pacemakers, and the microstimulators of the type disclosed in the above-referenced '539 patent, may always apply their stimulation pulses through the same electrodes. Other stimulating devices, e.g., cochlea stimulators of the type disclosed in the above-referenced '726 patent, however, apply the stimulus pulses, which are of varying amplitude and polarity, to different electrodes, or different electrode pairs, as a function of the sensed input signal. There is thus a need in the implantable stimulating device field to provide an output circuit for use with such devices that allows different electrode pairs to be selected through which stimulus currents having different amplitudes and polarities may be applied.
As medical devices have become more useful and numerous in recent years, there is a continual need to provide very low power sensors and stimulators that may be connected to, or incorporated within, such devices so that the desired function of the device can be carried out without the expenditure of large amounts of power (which power, for an implanted device, is usually limited). Moreover, there is a constant need and desire to make such implantable devices smaller and smaller.
To meet this need (smaller circuits, less power) within an implantable stimulating device, it has been common to design an output circuit for interfacing with the electrodes which selectively connects a single current source, or one of a plurality of current sources, to a selected electrode pair, rather than designing a separate current source for each electrode pair. In order to allow the polarity of the stimulus applied through the selected electrode pair to be changed without requiring an additional current source, which would tend to make the device larger and consume more power, it is also known to employ a switching matrix which selectively connects the selected electrode pair to either side of the current source, or which otherwise causes the current flow direction through the selected electrode pair to change. All such switching matrices, or equivalent schemes, require that the electrode nodes (those nodes connected directly to a given electrode) be physically or electrically switched from one circuit location to another. Disadvantageously, such “switching” requires additional circuitry which not only increases the impedance of the circuit connection path, but which also, during operation, takes time to complete, i.e., takes a finite time to switch the switching components from being biased ON (low impedance) or OFF (high impedance) so that the desired “connection” may be established or disconnected.
There is thus a need in the art for an output circuit useable within an implantable current stimulator that is small, operates at low power, and does not physically or electrically switch the electrode node from one circuit location to another as different and continually changing stimulus parameters (amplitude, polarity, electrode pairings) are needed.
SUMMARY OF THE INVENTION
The present invention addresses the above and other needs by providing a programmable output current source for use within an implantable tissue or nerve stimulator, e.g., an implantable cochlear stimulator, that does not switch a current or voltage source between different electrode pairs. Rather, each electrode node has parallel-connected P-FET current source sets permanently connected between it (the electrode node) and a positive voltage rail, and parallel-connected N-FET current source sets permanently connected between it (the electrode node) and a negative voltage rail. The P-FET current sources provide a programmable amount of current to the electrode node (i.e., the P-FET current sources “source” current to the electrode node) and the N-FET current sources receive the programmable amount of current from the electrode node (i.e., the N-FET current source “sink” current from the electrode node). It is thus never necessary to physically or electronically “switch” the electrode nodes between one or more circuit locations, or to “switch” the electrode node to a different side of a current or voltage source so as to change the polarity of the stimulus (current) flowing through the electrode node.
In accordance with one aspect of the invention, complementary sets of CMOS P-FET and N-FET current sources are fabricated on a semiconductor substrate in a relatively small area so as to be permanently connected to an electrode node. Such current sources operate at very low power levels, and when disabled (turned OFF) do not consume any power.
In accordance with another aspect of the invention, such P-FET and N-FET current source sets source or sink increasing amounts of current for each electrode node. That is, for example, a first P-FET current source included as part of the P-FET current source sets generates (sources), when enabled, a current of I to the electrode node, where I is a fixed, selectable current value; a second P-FET current source sources, when enabled, a current
2
I to the electrode node; a third P-FET current source sources, when enabled, sources a current
3
I to the electrode node; and so on, for up to n P-FET current sources, where n is an integer of n=0, 1, 2, 3, . . . n. In this manner, it is seen that each of the n P-FET current sources respectively generates (sources) a current of 2
n
I to the electrode node when enabled. Similarly, there are n N-FET current sources, each of which respectively generates (sinks) a current of 2
n
I from the electrode node.
In accordance with an additional aspect of the invention, sequences of current pulses, e.g., biphasic or multiphasic stimulation pulse pairs, are formed by combining individual current pulses having the desired polarity and timing relationship.
To illustrate this process, consider a biphasic pulse that is to be applied between electrodes
5
and
6
of sixteen electrodes. The biphasic pulse is to have a positive pulse having an amplitude of
3
I for 33 &mgr;sec, followed by a negative pulse of
3
I for 33 &mgr;sec. Such biphasic pulse is formed, using the present inven
Advanced Bionics Corporation
Gold Bryant R.
Kamm William E.
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