An electrical stimulator capable of achieving time interference

Abstract

The present invention discloses an electrical stimulator capable of achieving time interference, which includes a host computer, a digital chip, and a peripheral circuit; the host computer exchanges data with the digital chip through the UART interaction protocol; the digital chip is internally divided into two parts: a data control end and a data processing end; the peripheral circuit includes a DAC, an ADC, and a voltage-controlled current source circuit. Both the DAC and the ADC are connected to the digital chip. The DAC converts the digital control signal output by the digital chip into an analog voltage signal and outputs it. A voltage-controlled current source is externally connected after the DAC to convert the output analog voltage signal into a current signal; the real-time voltage signals of each electrode are obtained through the ADC. In the present invention, all calculation and control function modules are integrated on the same digital chip, and the peripheral circuit and the chip can be independently iterated without affecting each other, saving development costs; an impedance detection system is added, which can monitor the impedance conditions of each electrode in real time before and during the experiment, ensuring both the output safety and the accuracy of the signal output.

Description

Technical Field

[0001] The present invention relates to an electrical stimulator capable of achieving temporal interference. Background Art

[0002] Transcranial electrical stimulation (tES) is a non-invasive electrical stimulation technique. Because of its non-invasive characteristics, it causes less harm to the patient's body and mind, and has become a hot topic for brain function research and treatment in recent years. Different from transcranial magnetic stimulation (TMS) that generates current in the human body using a magnetic field, and traditional deep brain stimulation that requires surgery and drug treatment, transcranial electrical stimulation only needs to directly connect the electrodes placed on the corresponding parts of the human brain to release current stimulation. Most of them do not require complex systems and algorithms and can be designed to be cheaper, more convenient, and easier to use. Transcranial electrical stimulation can generally be classified according to the output stimulation waveform: transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and transcranial random noise stimulation (tRNS), etc.

[0003] Temporally Interfering (TI) is a special alternating current stimulation (tACS) method proposed in 2017. Compared with traditional tACS stimulation, TI needs to use high-frequency alternating current stimulation (greater than 1KHz) to input into the brain. Utilizing the characteristics of high-frequency signal stimulation with a deeper depth and a low-frequency envelope generated by two-channel stimulation signals with a frequency difference, it performs alternating current stimulation at a certain frequency on specific regions in the brain without interfering with the surrounding brain regions. Its stimulation frequency is determined by the envelope frequency generated by the frequency difference between the channels, so it is more sensitive to the parameter setting between the channels.

[0004] Currently, the commonly used stimulations in domestic and foreign clinical experiments are transcranial direct current stimulation and transcranial alternating current stimulation. Therefore, the commercially available devices on the market mainly provide direct current, low-frequency alternating current, or random signals, and most of them are foreign companies, such as Ne and Soterix Medical. There are almost no domestic commercially available devices, and most of them are direct current stimulations. The rest are mostly independently developed in laboratories. However, due to the late proposal time of temporal interference stimulation and the high requirement for the correlation of output signals between channels, there are almost no devices on the market that can support TI experiments.

[0005] The patent application with the publication number CN210384587U discloses a transcranial electrical stimulator, which proposes an electrical stimulator that can automatically adjust the output current through real-time monitoring of impedance parameters to complete relevant stimulation experiments. It is mainly divided into a power supply, a human-computer interaction module, a voltage regulation module, and an impedance detection module. The impedance detection module is used to realize the real-time detection of electrode impedance, and the method of ensuring the normal progress of the stimulation experiment is to enter the voltage regulation module through the returned data to adjust the output voltage in real time. However, this electrical stimulator only supports single-channel current stimulation, and only describes that the real-time output current can be adjusted through the host computer, without mentioning other parameters.

[0006] The patent application with the publication number CN112891734A discloses a high-precision transcranial electrical stimulation device, which designs a transcranial electrical stimulation device that can provide multi-channel high precision. A central electrode and each auxiliary electrode form a group, and the auxiliary electrodes are arranged around the central electrode. Multiple groups of stimulations can be configured simultaneously, which can improve spatial focusing, accuracy, stimulation effect, and aftereffect time. At the same time, this application also introduces a pre-scanning mechanism. As Figure 1 shown, the contact quality of each channel is tested before the formal stimulation to ensure the best contact state, and the stimulation mode of N×1 or 1×N can be realized. However, it cannot achieve multi-channel simultaneous stimulation and cannot meet the time interference stimulation requirements.

[0007] The patent application with the publication number CN209809314U discloses a transcranial electrical stimulator for real-time monitoring of stimulation current. As long as a control signal is generated through the interaction between the MCU and the host computer to generate a voltage, and then the voltage signal is used as a standard to control the constant current source module to output a fixed current into the load. At the same time, a resistor is connected in parallel with the load, and the stimulation current is monitored and displayed by detecting the voltage information at both ends of the fixed-value resistor to ensure safety. The method for ensuring safety and stimulation effect in this application is achieved by connecting a fixed-value resistor in parallel at both ends of the load, measuring the voltage at both ends of the resistor, and obtaining the current passing through the human body through a certain conversion. If the set threshold is exceeded, the stimulation is interrupted. This patent mainly focuses on single-channel DC stimulation and current monitoring. The impedance detection method is not applicable to multi-channel stimulation devices, and it does not discuss whether it is applicable to AC stimulation.

[0008] Transcranial electrical stimulation stimulates the corresponding brain regions of the brain by inputting current, activates or inhibits the excitability of neurons, thereby increasing or decreasing the activity of the brain regions. Using this method to regulate the brain to generate special waveforms or inhibit abnormal discharges in the brain to achieve the purpose of treating brain diseases. Therefore, for an electrical stimulation device, how to ensure output accuracy and safety is of utmost importance; at the same time, it needs to be optimized for time interference stimulation (TI), so the correlation of output between channels is also one of the considerations.

[0009] For traditional electrical stimulation devices, there are few supported parameters (usually only frequency and amplitude), the number of channels is low (mainly single-channel), most do not support expansion, the frequency output range is low and cannot meet the TI stimulation requirements. Most devices package all functions together, making modification difficult and resulting in a high iteration cost. Summary of the Invention

[0010] The object of the present invention is to overcome the deficiencies of the prior art and provide an electrical stimulator that integrates all computing and control function modules on the same digital chip, and the peripheral circuit and the chip can be independently iterated without affecting each other. At the same time, it can monitor the impedance of each electrode in real time before and during the experiment, ensuring both output safety and signal output accuracy.

[0011] The object of the present invention is achieved through the following technical solutions: An electrical stimulator capable of realizing time interference, comprising a host computer, a digital chip, and a peripheral circuit;

[0012] The host computer exchanges data with the digital chip through the UART interaction protocol, receives impedance data and displays it in real time while transmitting the output information of each channel configured by the user;

[0013] The digital chip is mainly divided into two parts according to different functions: a data control end and a data processing end. The data control end is responsible for the overall system process control: decoding the control signals transmitted from the host computer; responsible for impedance calculation and feeding it back to the host computer; the data processing end uses DDS to output configuration signals and performs complex preprocessing on the digital signals transmitted into the chip for subsequent impedance mathematical calculations;

[0014] The peripheral circuit includes a DAC, an ADC, and a voltage-controlled current source circuit. Both the DAC and the ADC are connected to the digital chip. The DAC converts the digital control signal output by the digital chip into an analog voltage signal and then outputs it. A voltage-controlled current source is connected externally after the DAC to convert the output analog voltage signal into a current signal and output it to each stimulation channel; the ADC collects the analog voltage signal to realize impedance detection, obtains the real-time voltage signal of each electrode through the ADC, processes this group of voltage signals in the digital chip, and finally feeds it back to the host computer for display in real time.

[0015] The host computer has a manual current calibration function, and the digital chip has an automatic current calibration function;

[0016] Automatic calibration is achieved by connecting a fixed reference resistor Ref in series at the front end of each stimulating channel electrode. Automatic calibration determines the current passing through the reference resistor based on the voltage across Ref. The specific method is as follows: The host computer configures the output parameters, processes the output current signal through digital core and sends it to each stimulating channel. The ADC collects the voltage across the fixed reference resistor Ref, calculates the current value passing through this channel at this time using Ohm's law, and determines the error between this current value and the required current value. If the error is greater than the preset threshold, the DDS is used to output a control word for compensation. Then, the voltage acquisition and current value calculation operations are repeated until the error between the current value of this channel and the required current value is less than or equal to the preset threshold, and the current value feedback signal of this channel is sent to the host computer for display.

[0017] Manual calibration adjusts the output by manually modifying parameters on the host computer. The priority of manual calibration is higher than that of automatic calibration.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1. Modular design with high functional integration. All computing and control function modules are integrated on the same digital chip. The remaining modules such as the host computer, ADDA, and voltage-controlled current source circuit can be replaced or modified at any time without affecting the internal logic of the digital chip, which can save development costs. At the same time, an impedance detection system is added to ensure output safety, which can monitor the impedance of each electrode in real time before and during the experiment. When the electrode impedance or output signal is abnormal, the host computer will display it in real time, ensuring both output safety and signal output accuracy.

[0020] 2. The settable parameters are rich and have a large range. It supports traditional electrical stimulation (tDCS, tACS) and supports the output of TI stimulation waveforms. The controllable parameters include: frequency, amplitude, phase, delay, and duration. In particular, the added phase adjustment can compensate for the phase shift error generated by analog output.

[0021] 3. Strong expandability and simple iteration. All logics are built into the digital chip, and its internal code can be iterated at any time without replacing the supporting software and hardware devices. Universal interfaces such as USB and network ports are reserved, which is convenient for subsequent customization and expansion according to requirements. Description of the Drawings

[0022] Figure 1 It is a schematic structural diagram of a high-precision transcranial electrical stimulation device;

[0023] Figure 2 It is a schematic structural diagram of the electrical stimulator capable of realizing time interference of the present invention;

[0024] Figure 3 It is a schematic structural diagram of an automatic calibration device;

[0025] Figure 4 This is a working flow chart of the electrical stimulation device capable of realizing time interference according to the present invention. DETAILED DESCRIPTION

[0026] The present invention first uses the same digital chip and its crystal oscillator to realize the output of all channels, ensuring the consistency of output timing and strong correlation between channels; and in order to avoid the possible signal offset of the output after passing through the analog circuit, phase control is specially added. If there is a phase offset in the output during the stimulation experiment, the phase can be manually adjusted; this device integrates all calculation and control function modules with the same digital chip, and the peripheral circuit and the chip can iterate independently without affecting each other, saving development costs; at the same time, in order to ensure the safety of the output, an impedance detection system is added, which can monitor the impedance of each electrode in real time before and during the experiment. When the electrode impedance or output signal is abnormal, the upper machine will display it in real time, ensuring the output safety while also ensuring the accuracy of the signal output. The technical solution of the present invention is further explained below with reference to the accompanying drawings.

[0027] like Figure 2 As shown, the present invention is an electrical stimulator that can realize time interference, including a host computer, a digital chip and a peripheral circuit; the three parts are designed to be independent of each other. While ensuring the consistency of the protocols between modules, any module can be modified or replaced at any time without adjusting other parts at the same time. This design facilitates subsequent maintenance and upgrades of the entire device and reduces iteration costs.

[0028] At the same time, since the present invention uses current stimulation, the voltage will change according to the load, and the output voltage is mainly determined by the impedance when the electrode contacts the human body. If the impedance is too high, the voltage may increase. At this time, continuing the stimulation experiment may burn the skin. Therefore, in order to ensure safety, the present invention has added an impedance detection system. In addition to real-time monitoring of the current electrode impedance information, it can also assist in observing the waveform output status to a certain extent. Because when the contact is good, if the impedance display suddenly changes too much, it means that there is an abnormality in the output and the experiment needs to be terminated to eliminate the error.

[0029] The host computer exchanges data with the digital chip through the UART interactive protocol, and receives impedance data and displays it in real time while transmitting the output information of each channel configured by the user; the range of each channel parameter is mainly linked to the transcranial electrical stimulation experiment, and TI stimulation needs to be taken into account. The frequency range is set to 50-10KHz, the maximum amplitude is 0.5-2mA, the duration can reach up to 1h with a step of 1s, and the maximum delay between channels can be set to 10min with a step of 1s. At the same time, the phase compensation range added is 2π, and the accuracy is 2π / 1024.

[0030] All control and data processing modules are integrated on the same chip. In this way, the same crystal oscillator can be used to control the output timing, ensuring strong correlation between channels. At the same time, it is convenient to iterate the internal design of the chip at any time without changing the design of external hardware. The preferred chip for this invention is FPGA because of its strong customization ability and simple iteration, which can reduce the development and subsequent maintenance costs. Internally, the digital chip is mainly divided into two parts according to different functions: the data control end and the data processing end. The data control end is responsible for the overall system process control: decoding the control signals transmitted from the host computer; being responsible for impedance calculation and feeding it back to the host computer; The data processing end uses DDS (Direct Digital Synthesis) to output configuration signals and performs complex preprocessing on the digital signals transmitted into the chip for subsequent mathematical calculation of impedance;

[0031] The peripheral circuits mainly include ADDA (analog-to-digital conversion circuit) and voltage-controlled current source circuit. ADDA is one of the necessary circuits for outputting and receiving analog signals, including DAC, ADC, and voltage-controlled current source circuit. Both DAC and ADC are connected to the digital chip. DAC converts the digital control signal output by the digital chip into an analog voltage signal and then outputs it. A voltage-controlled current source is externally connected after DAC to convert the output analog voltage signal into a current signal and output it to each stimulation channel; ADC collects analog voltage signals to achieve impedance detection. The real-time voltage signals of each electrode are obtained through ADC, and this group of voltage signals is processed inside the digital chip and finally fed back to the host computer for display in real time.

[0032] Since the maximum output of the operational amplifier chip of the voltage-controlled current source circuit adopted in this invention can only reach 12V, and when the current output is fixed, the output voltage is related to the impedance size, the impedance threshold is set to 5KΩ. However, during actual measurement, it can be relaxed according to the change of output current and can reach 10KΩ.

[0033] To ensure the stability and safety of stimulation, current automatic calibration and manual calibration functions are added to the digital chip and the host computer respectively. Automatic calibration calibrates the output current before stimulation, corrects the overall output current during stimulation, monitors the overall circuit current output situation, and assists in judging the electrode impedance situation. Manual calibration can compensate the current output parameters (mainly frequency and amplitude) at any stage of the experiment;

[0034] Automatic calibration is achieved by connecting a fixed-value reference resistor Ref (such as 1KΩ) in series at the front end of each stimulation channel electrode, as Figure 3 shown Figure 3It is the structure of a dual-channel electrical stimulator. In the figure, in1 and in2 are input currents, Ref1 and Ref2 are reference resistors, R1, R2, R3, and R4 represent electrode resistances, and Rt is the simplified human impedance.

[0035] Automatic calibration determines the current passing through the reference resistor based on the voltage across Ref; the specific method is as follows: The host computer configures the output parameters (mainly configuring the current amplitude), and after digital core processing, outputs a current signal to each stimulation channel. The ADC collects the voltage across the fixed-value reference resistor Ref, calculates the current value passing through this channel at this time using Ohm's law, and judges the error between this current value and the required current value. If the error is greater than the preset threshold (5%), the DDS output control word is used for compensation; then the voltage acquisition and current value calculation operations are repeated until the error between the current value of this channel and the required current value is less than or equal to the preset threshold, and the current value feedback signal of this channel is sent to the host computer for display;

[0036] During calibration, each channel will stagger the stimulation time. The stimulation time stagger between channels is at the second level to prevent mutual influence, while the short-term stimulation time of each channel is controlled at the millisecond level because it cannot affect subsequent stimulation experiments.

[0037] A certain degree of automatic calibration is also carried out during the stimulation experiment. The stimulation experiment mainly uses a sine wave and stimulates both channels simultaneously. It cannot be directly calculated and needs to be processed by FFT after windowing to separate the voltage conditions of each reference point. The signal error after FFT processing is relatively large and may not be able to be accurately calibrated. Therefore, the frequency and accuracy of automatic calibration need to be reduced during the experiment, and automatic calibration will be used as an auxiliary judgment criterion for impedance detection. According to Ohm's law, the overall voltage divided by the overall resistance gives an estimated current value. If the difference between this value and the current flowing through the reference resistor after estimation is too large, it indicates that there may be a problem with the electrode impedance or current input. At this time, the experiment needs to be terminated to find the reason, which can ensure the safety and stability during the stimulation experiment to the greatest extent.

[0038] Manual calibration adjusts the output by manually modifying parameters on the host computer. It is an alternative to automatic calibration. When the automatic calibration cannot reach the acceptable error range or in some special cases (such as automatic calibration failure, the reliability of automatic calibration has not been up to the requirements during the experiment, etc.), compensation parameters need to be manually set. The priority of manual calibration is higher than that of automatic calibration and can be carried out at any time during the stimulation experiment. Manual calibration needs to be judged by observing the parameters displayed on the host computer. The specific parameters that need to be displayed on the host computer are: the voltage across the fixed-value reference resistor at the front end of the electrode and the calculated current conditions of each channel, the total voltage conditions of each channel, and the estimated current value of each channel calculated according to the impedance detection situation. Generally, manual calibration is not required, and calibration may only be needed when the current conditions of each channel displayed on the host computer and the estimated current value after impedance detection have a large error.

[0039] The specific parameters for the host computer control / display are as follows: the output parameter configuration of each channel (waveform, frequency, amplitude, phase, duration, delay time), which can be configured directly, the impedance situation of each electrode, the estimated current value of each channel, the voltage situation of each reference point after FFT processing during the experiment (the voltage across the reference resistor and the voltage of each channel), the theoretical waveform drawn according to the set parameters and the real-time envelope waveform drawn according to the voltage acquisition situation of each point, the impedance situation of each electrode, and the printing of necessary information.

[0040] The main execution flow chart of the present invention is as Figure 4 shown. After connecting the hardware and the PC, after configuring the output configuration parameters on the host computer, turn on the hardware to start the pre-stimulus impedance measurement, and judge whether the impedance meets the range. This step is to ensure good contact between the electrode and the skin and prevent excessive instantaneous voltage from burning the skin. If there is an abnormality in the impedance measurement on the host computer, the abnormal electrode needs to be adjusted and then re-measured until the impedance reaches the set threshold, and the host computer reconfigures the required parameters of each channel to start the stimulus output. During the stimulation experiment, the present invention will detect the impedance of each electrode in real time, which is not only a guarantee of safety but also a verification of the output signal. If an impedance detection abnormality occurs during the experiment, immediately interrupt the experiment, adjust the corresponding electrode record situation, and then decide whether to restart the entire experiment. If no abnormality occurs all the time, then continuous stimulation will be carried out until the set time is reached, the output is terminated, and the stimulation ends.

[0041] The core processing steps are all built into the digital chip. The host computer and the peripheral circuit can be modified at any time under the condition of meeting the interaction protocol, which greatly expands the flexibility of the entire system. At the same time, instead of using the traditional DDS chip, it is designed independently, expanding the range of modification, and can customize the required output signal to the greatest extent, which is convenient for subsequent iterative updates.

[0042] Those of ordinary skill in the art will realize that the embodiments described herein are for helping the reader understand the principles of the present invention, and it should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. An electrical stimulator capable of achieving time interference, characterized in that, It includes a host computer, a digital chip and peripheral circuits; The host computer exchanges data with the digital chip through the UART interaction protocol, receives impedance data while transmitting the output information of each channel configured by the user and displays it in real time; the parameter ranges of each channel are related to transcranial electrical stimulation experiments, and considering TI stimulation, the frequency range is set to 50 - 10KHz, the maximum amplitude is 0.5 - 2mA, the maximum duration reaches 1h and the step is 1s, the maximum inter-channel delay is set to 10min and the step is also 1s, and the added phase compensation range is 2π, with an accuracy of 2π / 1024; The digital chip is mainly divided into two parts according to different functions: a data control end and a data processing end. The data control end is responsible for the overall system process control: decoding the control signals transmitted from the host computer; being responsible for impedance calculation and feeding it back to the host computer; the data processing end uses DDS to output configuration signals and performs complex preprocessing on the digital signals transmitted into the chip for subsequent impedance mathematical calculations; all control and data processing modules are integrated on the same chip, and the same crystal oscillator is used to control the output timing to ensure strong correlation between channels; The peripheral circuits include a DAC, an ADC, and a voltage-controlled current source circuit. Both the DAC and the ADC are connected to the digital chip. The DAC converts the digital control signal output by the digital chip into an analog voltage signal and then outputs it. A voltage-controlled current source is externally connected after the DAC to convert the output analog voltage signal into a current signal and output it to each stimulation channel; the ADC collects the analog voltage signal to achieve impedance detection. The real-time voltage signals of each electrode are obtained through the ADC, and this group of voltage signals is processed in the digital chip and finally fed back to the host computer for display in real time.

2. The electrical stimulator capable of realizing time interference according to claim 1, wherein The host computer has a manual current calibration function, and the digital chip has an automatic current calibration function; The automatic calibration is achieved by connecting a fixed-value reference resistor Ref in series at the front end of each stimulation channel electrode. The automatic calibration judges the current passing through the reference resistor according to the voltage across Ref. The specific method is: the host computer configures the output parameters, and after being processed by the digital core, outputs a current signal to each stimulation channel. The ADC collects the voltage across the fixed-value reference resistor Ref, and uses Ohm's law to calculate the current value passing through this channel at this time, and judges the error between this current value and the required current value. If the error is greater than the preset threshold, the DDS is used to output a control word for compensation; then the voltage collection and current value calculation operations are repeated until the error between the current value of this channel and the required current value is less than or equal to the preset threshold, and the current value feedback signal of this channel is fed back to the host computer for display; The manual calibration adjusts the output by manually modifying the parameters on the host computer, and the manual calibration has a higher priority than the automatic calibration.

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