Patent Publication Number: US-2012035687-A1

Title: Implantable electrical stimulator

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 099126334, filed Aug. 6, 2010, which is herein incorporated by reference. 
     BACKGROUND 
     1. Field of Invention 
     The present invention relates to an electronic device. More particularly, the present invention relates to an electrical stimulator. 
     2. Description of Related Art 
     Nerve dysfunctions belong to a main category of neurological diseases. Although pain is interpreted as the fifth vital sign by many professions, the presence of different degrees of pain significantly affects quality of life for many patients, especially the elderly. 
     Current treatments to these neurological diseases are quite complicated. For example, acupuncture electrodes connecting to bulky medical apparatus are inserted in to the body of the subject during each treatment. The insertion of the acupuncture electrodes may cause pain to the subject, and increase the possibility of infections. 
     In view of the foregoing, there is an urgent need in the related field to provide a way to reduce pain to the subject. 
     SUMMARY 
     The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the present invention or delineate the scope of the present invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later. 
     In one aspect, the present invention is directed to implantable electric stimulator adapted to be implanted into the body a subject. 
     According to one embodiment of the present invention, the implantable electric stimulator comprises two stimulating electrodes, a system-on-chip and an inductive coil. In structure, the system-on-chip electrically connects the stimulating electrodes, and the inductive coil is electrically connected to the system-on-chip. In operation, an external power supply may wirelessly charge the system-on-chip via the inductive coil, whereas the system-on-chip may apply electric stimulation to a dorsal root ganglion through the stimulating electrodes. As such, it is possible to ameliorate the pain by applying electric stimulation to the dorsal root ganglion. 
     According to another embodiment of the present invention, the implantable electric stimulator comprises two stimulating electrodes, a system-on-chip, and a receiving coil. In operation, the stimulating electrodes is electrically connected to a dorsal root ganglion, the receiving coil is inductively coupled to the output coil of an external power supply so that the external power supply is operable to wireless charge the system-on-chip, and the system-on-chip outputs electric stimulation via the stimulating electrodes. As such, the pain of the subject being treated could be alleviated when the dorsal root ganglion are subjected to electric stimulation. 
     In view of the foregoing, the technical solution provided by the present disclosure exhibits obvious advantages and beneficial effects as compared with conventional techniques. The technical solution embodies substantial technical progress and provides a wide range of industrial utilities. The advantages provided by the present disclosure include: 
     1. The system-on-chip is wireless charged, and hence, no plug sockets or batteries are required for charging; as such, the present implantable electrical stimulator is portable and easy-to-use; and 
     2. The functionality of the stimulator is embodied in the system-on-chip thereby miniaturizing the volume of the present implantable electric stimulator so that it is suitable to be implanted in to human body; as such, patients would no longer suffer from the uncomfortable cause by the insertion of the acupuncture electrodes during each treatment. 
     Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein: 
         FIG. 1  is a schematic diagram illustrating an implantable electric stimulator according to one embodiment of the present disclosure; 
         FIG. 2  is a circuit diagram of the rectifier depicted in  FIG. 1  according to one embodiment of the present disclosure; 
         FIG. 3  is a circuit diagram of the voltage limiter depicted in  FIG. 1  according to one embodiment of the present disclosure; 
         FIG. 4  is a circuit diagram of the regulator depicted in  FIG. 1  according to one embodiment of the present disclosure; 
         FIG. 5  is a circuit diagram of the clock regenerator depicted in  FIG. 1  according to one embodiment of the present disclosure; 
         FIG. 6  is a circuit diagram of the radio frequency receiver depicted in  FIG. 1  according to one embodiment of the present disclosure; 
         FIG. 7  is a circuit diagram of the power-on reset circuit depicted in  FIG. 1  according to one embodiment of the present disclosure; 
         FIG. 8  is a circuit diagram of the driver depicted in  FIG. 1  according to one embodiment of the present disclosure; and 
         FIG. 9  is a time sequence diagram of the pulse signal outputted by the driver depicted in  FIG. 1  according to one embodiment of the present disclosure. 
     
    
    
     Like reference numerals are used to designate like parts in the accompanying drawings. 
     DETAILED DESCRIPTION 
     The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples. Also, well-known elements and/or steps are not discussed in the embodiments in detail for the sake of clarity and brevity. 
       FIG. 1  is a schematic diagram illustrating an implantable electric stimulator according to one embodiment of the present disclosure. As shown in  FIG. 1 , the implantable electric stimulator may include a system-on-chip  100 , an inductive coil (receiving coil)  200 , and two stimulating electrodes  181 ,  182 . The implantable electric stimulator may be implanted into the human body and is positioned under the skin  510  so as to stimulate the dorsal root ganglion  500  of the spine. 
     In structure, the inductive coil  200  is electrically connected to the system-on-chip  100 , the system-on-chip  100  electrically connects the stimulating electrodes  181 ,  182 , and the stimulating electrodes  181 ,  182  are used for electrically connecting the dorsal root ganglion  500 . In operation, the external power supply  300  may wirelessly charge the system-on-chip  100  via the inductive coil  200 , and the system-on-chip  100  may apply electrical stimulation to the dorsal root ganglion  500  through the stimulating electrodes  181 ,  182 . Dorsal root ganglion  500  is a nodule on a dorsal root that contains cell bodies of neurons of peripheral nervous system which is responsible for transmitting sensory information along each of the peripheral axons. The sensory information is electrochemical signals representing senses of touch, pain, temperature, etc. The sensory information is then integrated by the central nervous system so that the brain may perceive the specific sense. As such, it is possible to alleviate the pain by electrically stimulating the dorsal root ganglion  500 . 
     In practice, the power is transferred by means of the mutual induction between the inductive coil (output coil)  310  of the external power supply  300  and the inductive coil (receiving coil)  200  of the implantable electric stimulator. In the field of the wireless power transmission, one of the most important concerns is to improve the efficiency of the power transmission. As such, in one embodiment, the external power supply  300  may include a Class-E power amplifier, which may provide higher power transmission efficiency as compared with other types of power amplifiers. Accordingly, problems such as the wireless signal is too weak to be recognized or the power is not sufficient for the system-on-chip  100  can be avoided. 
     Also, the choice of the frequency band at least depends on the distance that the wireless signal should traverse in the human tissue. Generally, the high-frequency signals have shorter depth of penetration in human body, as compared with short-frequency signals. As such, in one embodiment, the frequency of the wireless signal is about 1 MHz. 
     As shown in  FIG. 1 , the system-on-chip  100  may include elements such as: a rectifier  110 , a voltage limiter  120 , a regulator  130 , a clock regenerator  140 , a radio frequency receiver  150 , controller  160  and driver  170 . In the present embodiment, the above-identified elements are integrated into the system-on-chip  100  so as to miniaturize the volume of the implantable electric stimulator. 
     It should be appreciated that by manufacturing the above-identified elements as individual chips and disposing such chips on a circuit board, the chips should be packaged separately. As such, the chips (elements) may occupy extra space (as compared with the integrated elements provided in the present embodiment), and additional wirings are required to connect these chips, thereby increasing the volume of the electric stimulator. However, larger electric stimulators may raise the chances of infections of the subjects and cause uncomfortableness to the subjects. 
     In addition, the system-on-chip  100  may be encapsulated by a bio-compatible material so as to facilitate the implantation. For example, the bio-compatible material may be Poly (dimethylsiloxane) (PDMS). PDMS can be used as a protection layer to seal the system-on-chip  100 . Analysis performed by the present inventor shows that this encapsulation exhibits satisfactory hermeticity, tensile property, and flexibility. Also, this encapsulation can readily adhere to the human tissue and provide suitable strength. 
     The mechanism of the electric energy conversion of the employed by the system-on-chip  100  is implanted by the rectifier  110 , the voltage limiter  120 , and the regulator  130 . In structure, the controller  160  is electrically connected to the regulator  130 , the regulator  130  is electrically connected to the voltage limiter  120 , the voltage limiter  120  is electrically connected to the rectifier  110 , and the rectifier  110  is electrically connected to the inductive coil  200 . 
     In operation, the wireless signal provided from the external power supply  300  may be rectified by the rectifier  110  to obtain a direct current through the induction coupling between the inductive coil  200  and the inductive coil  310  of the external power supply  300 . Then, the voltage limiter  120  may limit the voltage of the direct current to a value lower than a predetermined voltage so that the voltage would not exceed the system load. Afterwards, the regulator  130  may regulate the direct current to obtain a steady voltage, remove the noise, and provide the steady voltage to the controller  160  so that the controller  160  has sufficient electric energy to generate a stimulus signal. In the present embodiment, in order to improve the driving force outputted by the controller  160 , and avoid the distortions of the stimulus signal, a driver  170  is employed to enhance the stimulus signal, and the enhanced stimulus signal is outputted to the dorsal root ganglion  500  via the stimulating electrodes  181 ,  182 . 
     Specifically, the mechanism of providing the electric stimulation may be implanted by the clock regenerator  140  in conjunction with the controller  160  and the driver  170 . In structure, the stimulating electrodes  181 ,  182  are electrically connected to the driver  170 , the driver  170  is electrically connected to the controller  160 , the controller  160  is electrically connected to the clock regenerator  140 , and the clock regenerator  140  is electrically connected to the is inductive coil  310 . 
     In operation, the wireless signal provided from the external power supply  300  is converted into working clock(s) for the controller  170  through the induction coupling between the inductive coil  200  and the inductive coil  310  of the external power supply  300 , and thereby, the controller  160  may generate stimulus signal(s) based on the working clock(s). Thereafter, the stimulus signal, after being enhanced by the driver  170 , is outputted to the dorsal root ganglion  500  via the stimulating electrodes  181 ,  182 . 
     In addition, a modulated parameter instruction may be provided to the system-on-chip  100  through an external radio frequency transmitter  400 , so as to control the waveform outputted by the implantable electric stimulator. In one embodiment, the above-mentioned mechanism may be implanted by the collaboration of the radio frequency receiver  150  and the controller  160 . In structure, the controller  160  is electrically connected to the receiver  150 , and the receiver  150  may wirelessly communicate with the radio frequency transmitter  400 . 
     In operation, when the modulated signal transmitted by the radio frequency transmitter  400  penetrates the skin  510  and reaches the system-on-chip  100 , the radio frequency receiver  150  may obtain and demodulate the modulated signal to output a demodulated signal so that the controller  160  may set the parameter(s) for the stimulus signal based on the demodulated signal. For example, if the stimulus signal is a pulse, the parameter thereof may be the carrier frequency, the cycle time (period) and/or the duty cycle, etc.; whereas if the stimulus signal is a sine wave, the parameter thereof may be the cycle (period) and/or the amplitude, etc. 
     In one embodiment, the radio frequency transmitter  400  and the external power supply  200  may be integrated in a single electronic device, such as a cellular phone or other portable electronic devices. As such, the wireless charging of the implantable electric stimulator and the intensity and duration of the electric stimulation may be achieved simply by operating the cellular phone. 
     In practice, the circuit framework of the system-on-chip  100  is embodied by the 0.35 micrometer CMOS process by TSMC. In such circuit framework, the efficiency of the conversion from the wireless signal into the direct current is about 80%, the wave amplitude of the radio frequency transmission may be no less than 3 V, the frequency of the wireless signal provided by the external power supply  300  is about 1 MHz, the frequency of the modulated obtained by the signal radio frequency receiver  150  is about 402 MHz, the sensitivity of the radio frequency receiver  150  is about −62 dBm, the voltages outputted by the stimulating electrodes  181 ,  182  are limited to 5 V at maximum, whereas the voltage of about 3 V is sufficient to substantially alleviate or relive the pain. 
     Also, since the proteins of the human body may start to denature at about 41′C, the operating temperature of the system-on-chip  100  should not exceed 39′C. The size of the system-on-chip  100  is about 2.159 mm*2.146 mm which is suitable for being implanted into the human body. 
     Detailed descriptions of each of the elements illustrated in in system-on-chip  100  are provided hereinbelow in connection with  FIG. 2  to  FIG. 8  so as to facilitate the understanding to the above-mentioned circuit framework. 
       FIG. 2  is a circuit diagram of the rectifier  110  depicted in  FIG. 1  according to one embodiment of the present disclosure. As shown in  FIG. 2 , the rectifier  110  includes transistors, P-type metal oxide semiconductors Mp 1 , Mp 2  and N-type metal oxide semiconductors Mn 1 , Mn 2 , which are disposed and connected as a diode. 
     In the present embodiment, the P-type metal oxide semiconductors and the N-type metal oxide semiconductors are connected as a backward diode and assembled as a bridge-type full wave rectification. When the wireless signals are inputted from the two terminals of the differential motion, a full wave voltage may be generated at the output, wherein the rectification is achieved mostly by the diode formed at the P-N junction between the source and the body structure. The advantage of such framework lies in that only metal oxide semiconductors are required to implant the functionality of the rectification. 
       FIG. 3  is a circuit diagram of the voltage limiter  120  depicted in  FIG. 1  according to one embodiment of the present disclosure. As shown in  FIG. 3 , the voltage limiter  120  includes a plurality of diodes  121 , a resistor  122  and a P-type metal oxide semiconductor  123 . 
     In operation, a voltage limiter  120  is disposed behind the rectifier  110  to prevent the damage to the circuit caused by the instantaneous conducted current or voltage that are higher than a predetermined level. When the output voltage exceeds the predetermined level, the diode(s)  121  of the voltage limiter  120  would be conducted and limit the output voltage under a predetermined voltage. The value of the predetermined voltage depends on the number of the diodes  121  serial-connected. Moreover, each of the diodes  121  is implemented by the P-type metal oxide semiconductor in the form of a diode. 
       FIG. 4  is a circuit diagram of the regulator  130  depicted in  FIG. 1  according to one embodiment of the present disclosure. In the present embodiment, the regulator  130  is a low-dropout regulator. In practice, small volume and low power consumption are requisites to the present system-on-chip of the implantable electric stimulator. Hence, as compared with the general switching regulators and direct-current-to-direct-current converters, the low-dropout regulator used herein is advantageous in that the response time of the outputted voltage to the variation of the inputted voltage or load is faster, the ripple and noise of the outputted voltage is lower, and the circuit architecture is simpler. Also, the size of the present electric stimulator could be miniaturized, and the manufacturing cost could be reduced. Also, it should be noted that the intrinsic properties of the present low-dropout regulator (such as the quiescent current, voltage drop and noise) is significantly enhanced by the present design where the low-dropout regulator is manufactured by a CMOS process that provide a compact product with low manufacturing cost. 
     As shown in  FIG. 4 , the low-dropout regulator  130  includes an energy gap reference voltage circuit  132  and a voltage regulator. In structure, the energy gap reference voltage circuit  132  is electrically connected to the voltage regulator. In operation, the voltage regulator received the voltage outputted from the voltage limiter  120  and regulates the desired steady direct voltage (such as, 3 V) for use as the energy source for the rest segments of the chip. 
     In practice, the voltage regulator includes a lock loop consisting of an amplifier  134  in conjunction with metal oxide semiconductor field effect transistor  135  and resistors  136 ,  137 . The voltage regulator  133  requires an accurate reference voltage, and as such, an energy gap reference voltage circuit  132  is employed in the present embodiment to generate a steady power source that would not shift with the temperature variation. 
     Conventionally, the elevation or drop of the temperature may affect the parameters for the semiconductor manufacturing process so that the initially designed voltage and current would shift. However, the energy gap reference voltage circuit  132  is designed to get rid of the effects caused by temperature by using semiconductor elements having different positive and negative temperature coefficients to mutually offset the temperature effects. To conventional CMOS processes, resistors and metal oxide semiconductor field effect transistor have positive temperature coefficients; that is, the resistance value of the resistor and the threshold voltage of the semiconductor field effect transistor would increase as the temperature increase, which is disadvantageous to CMOS processes. As such, a direct solution to this disadvantage is to use the material(s) currently used in the process to form diodes or bipolar transistors Q 1 , Q 2 , so that the material(s) having a negative temperature coefficient is operable to compensate the temperature variation. 
       FIG. 5  is a circuit diagram of the clock regenerator  140  depicted in  FIG. 1  according to one embodiment of the present disclosure. As shown in  FIG. 5 , the clock regenerator  140  consists essentially of metal oxide semiconductor field effect transistors M 1 , M 2 , M 3 , M 4 , M 5 , and M 6 . In operation, the clock regenerator  140  may convert wireless signal having sine waveforms into a working clock having a square waveform, and then output the working clock to the controller through the output terminal  147 . 
       FIG. 6  is a circuit diagram of the radio frequency receiver  150  depicted in  FIG. 1  according to one embodiment of the present disclosure. As shown in  FIG. 6 , the radio frequency receiver  150  includes a radio frequency antenna  151 , a head amplifier  152 , a cascade amplifier  153 , an envelope detector  154 , and a comparator/buffer circuit  155 . 
     In structure, the radio frequency antenna  151  is electrically connected to the head amplifier  152 , the head amplifier  152  is electrically connected to the cascade amplifier  153 , the cascade amplifier  153  is electrically connected to the envelope detector  154 , and the envelope detector  154  is electrically connected to the comparator/buffer circuit  155 . 
     In operation, the radio frequency antenna  151  may receive a modulated signal from the radio frequency transmitter  400 , the amplifiers  152  and  153  may amplify the modulated signal, the envelope detector  154  may detect the envelope of the amplified modulated signal to output a detected signal for the comparator disposed at the front end of the circuit  155  to determine the voltage level of the detected signal thereby obtaining a demodulated signal, and the buffer disposed at the rear end of the circuit  155  outputs the demodulated signal to the controller  160  shown in  FIG. 1 . 
     The envelope detector  154  characterized in that the current and voltage of its circuit are relatively steady when the power source is shifted significantly, and hence the current and voltage would not greatly vary depending on the shift of the power source. As such, it is possible to generate a detected signal having a relatively steady direct current level by using the modulated signal as an inputting power source voltage, thereby accomplishing the functionality for detecting the envelope of the modulated signal. 
     The voltages of the detected signal generated by the envelope detector  154  would have overlapping portions, and hence, a comparator is used to determine the voltage level of the detected signal thereby obtaining a demodulated signal. The buffer is disposed at the rear end of the circuit  155 . The controller  160  is connected to the back end of the output terminal (OUT), and hence, the driving force of the output should be increase to avoid the distortion of the signal. 
       FIG. 7  is a circuit diagram of the power-on reset circuit  190  depicted in  FIG. 1  according to one embodiment of the present disclosure. In structure, the power-on reset circuit  190  may be integrated into the system-on-chip  100 , and electrically connected to the controller  160  shown in  FIG. 1 . In operation, when the wireless charging is carried out by the external power supply  300 , the power-on reset circuit  190  may reset the controller  160 . In the present embodiment, the power-on reset circuit  190  has a set of inverters  191  for increasing the driving force of the output, and a resetting signal is outputted to the controller shown in  FIG. 1 . 
       FIG. 8  is a circuit diagram of the driver  170  depicted in  FIG. 1  according to one embodiment of the present disclosure. As shown in  FIG. 8 , the driver  170  includes a first set of inverters  171  and a second set of inverters  172 . In structure, the first set of inverters  171  is electrically connected to the stimulating electrode  181 , whereas the second set of inverter  172  is electrically connected to the stimulating electrode  182 . In operation, since the stimulating electrodes  181 ,  182  are connected to the dorsal root ganglion  500 , it is required to increase the driving force of the output by the driving circuits consisting of inverters, so as to avoid the distortion of the stimulus signal being transferred into the human body. 
     Moreover, the controller  160  shown in  FIG. 1  may be a logic controller, digital controller, logic control circuit, programmable logic controller, programmable digital controller or the same. The controller  160  may have a pulse-width modulating device. The pulse-width modulating device may periodically output at least one pulse for use as the stimulus signal, and then the pulse signal is outputted by the driver  170 . 
       FIG. 9  is a time sequence diagram of the pulse signal outputted by the driver  170  depicted in  FIG. 1  according to one embodiment of the present disclosure. In practice, the carrier frequency of the pulse signal is in the range of about 4 kHz to about 1 MHz, and the cycle time thereof is about 0.05 seconds to about 1.25 seconds, and the duty cycle may be adjusted in the range from 0% to 100%. In other embodiments, the waveform of the stimulus signal generated by the controller  160  may be a sine wave, triangular wave or other mixed wave. 
     It will be understood that the above description of embodiments is given by way of example only and that various modifications may be made by those with ordinary skill in the art. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments of the invention. Although various embodiments of the invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those with ordinary skill in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention.