Implantable stimulation devices are devices that generate and deliver electrical stimuli to nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as is disclosed in U.S. Pat. No. 6,516,227. However, the present invention may find applicability in any implantable medical device system.
As shown in FIG. 1, an SCS system typically includes an Implantable Pulse Generator (IPG) 10, which includes a biocompatible device case 12 formed of titanium for example. The case 12 typically holds the circuitry and battery 14 necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 10 is coupled to electrodes 16 via one or more electrode leads (two such leads 18 and 20 are shown), such that the electrodes 16 form an electrode array 22. The electrodes 16 are carried on a flexible body 24, which also houses the individual signal wires 26 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 18, labeled E1-E8, and eight electrodes on lead 20, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary. The leads 18 and 20 couple to the IPG 100 using lead connectors 28, which are fixed in a header material 30 comprising an epoxy for example. In a SCS application, electrode leads 18 and 20 are typically implantable in a patient's spinal cord.
FIG. 2 shows plan view of an external controller 50 used to communicate with the IPG 10, and FIG. 3 shows both the external controller 50 and IPG 10 in cross section. The external controller 50, such as a hand-held programmer or a clinician's programmer, is used to send data to and receive data from the IPG 10. For example, the external controller 50 can send programming data such as therapy settings to the IPG 10 to dictate the therapy the IPG 10 will provide to the patient. Also, the external controller 50 can act as a receiver of data from the IPG 10, such as various data reporting on the IPG's status.
As shown in FIG. 3, the IPG 10 typically includes an electronic substrate assembly including a printed circuit board (PCB) 34, to which various electronic components 37 are mounted; some of these components are discussed subsequently with respect to FIG. 4. Two coils (antennas) are generally present in the IPG 10: a telemetry coil 36 used to transmit/receive data to/from an external controller 50; and a charging coil 38 for charging or recharging the IPG's battery 14 using an external charger (not shown). The telemetry coil 36 can be mounted within the header 30 of the IPG 10, but is located within the case 12 as shown, and as disclosed in U.S. Patent Application Publication 2011/0112610. The perspective drawing to the right of FIG. 3 shows the telemetry coil 36 in the IPG 10, which generally encompasses an area A2 and comprises a number of turns N2. (The case 12 has been omitted from this drawing to ease viewing of the telemetry coil 36).
The external controller 50, like the IPG 10, also contains a PCB 52 on which electronic components 54 are placed to control operation of the external controller 50; some of these components are also discussed with respect to FIG. 4. The external controller 50 is powered by a battery 56, but could also be powered by plugging it into a wall outlet for example. A telemetry coil 58 is also present in the external controller 50.
The external controller 50 typically comprises a graphical user interface 60 similar to that used for a portable computer, cell phone, or other hand held electronic device. The graphical user interface 60 typically comprises touchable buttons 62 and a display 64, which allows the patient or clinician to operate the external controller 50 to send programs to the IPG 10 and to review any relevant status information that has been reported from the IPG 10.
Wireless data transfer between the IPG 10 and the external controller 50 preferably takes place via magnetic inductive coupling, although a higher radiofrequency link could also be used. To implement indicative coupling functionality, the IPG 10 and the external controller 50 have telemetry coils 36 and 58 as previously mentioned. Either coil can act as the transmitter or the receiver, thus allowing for two-way communication between the two devices. This means of communicating by inductive coupling is transcutaneous, meaning it can occur through the patient's tissue 25.
Referring to FIG. 4, when data originating in the external controller's control circuitry 70 (e.g. a microcontroller) is to be sent from the external controller 50 to the IPG 10, that digital data (TX data) is sent to a modulator 73, where each bit is modulated appropriately in accordance with its data state. For example, if a Frequency Shift Keying (FSK) communications protocol is used, modulator 73 will convert each of the bits to one of two frequencies, f1 or f0, depending on their logic states. f1 may equal 129 kHz, and f0 may equal 121 kHz in one example. This resulting modulated signal can then be amplified 75, and presented to an LC circuit comprising a capacitor 77 and coil 58, which acts as an inductor. The LC circuit is tuned to generally resonate at a center frequency appropriate for the modulated data; for example, values for L and C may be chosen to tune the LC circuit to 125 kHz at the center between f1 and f0. Because LC circuit has some bandwidth, it can generally transmit and receive frequencies close to its center, such as f1 and f0.
The modulated data causes the LC circuit to resonate, and creates an AC modulated magnetic field 80, which is received at the coil 36 in the IPG 10. The IPG 10, like the external controller 50, also comprises an LC circuit comprising a capacitor 97 and coil 36, which again is tuned to the same center frequency of the AC modulated magnetic field (e.g., 125 kHz), and thus capable to receive f1 and f0 which are close to this frequency. The received signal may be amplified 96 and demodulated 94 to recover the original data (RC data). This received data is then sent to the IPG 10's control circuitry 90 (e.g., a microcontroller) for action. If the communication involves adjustment to the therapy the IPG 10 is providing to the patient, the control circuitry 90 communicates relevant instructions to stimulation circuitry 27. As is known, stimulation circuitry 27 includes various current or voltage sources which can be coupled to selected electrodes 16 to provide desired therapy to the patient. Such therapy, typically referred to as a stimulation program, generally specifies various parameters for the stimulation, such as which electrodes 16 are active, whether such electrodes act as anodes (current sources) or cathodes (current sinks), and the duration, frequency, and amplitude of pulses formed at the electrodes. See, e.g., U.S. Patent Application Ser. No. 61/654,603, filed Jun. 1, 2012, for further details concerning stimulation circuitry 27.
Transmission in the other direction—from the IPG 10 to the external controller 50—essentially occurs in the same manner, and similar transmission circuitry (93, 95) in the IPG 10 and reception circuitry (76, 74) in the external controller 50 are present. In both devices, control circuitries 70 and 90 issue a control signal RC/*TX, which informs whether that device is currently transmitting or receiving. For example, when transmitting from the external controller 50, RC/*TX would equal ‘0’ in that device (indicating transmission), while this same control signal would have the opposite state (1′) in the IPG 10 (indicating reception). Control signal RC/*TX can also be used to enable or disable various aspects of the communication circuitry. For example, if RC/*TX=0 in a given device, its reception circuitry (e.g., 76 and 74, or 96 and 94) would be disabled, while its transmission circuitry (73 and 75, or 93 and 95) would be enabled.