KR101508158B1 - Control of electrical offset volage in Functional Electrical Stimulation system - Google Patents

Abstract

An electric stimulation system using an electrode body includes an electrode body for applying a stimulation current to a conductive medium, a stimulation current generating unit for generating the stimulation current by using an input pulse and inputting the stimulation current to the electrode body, And a sample and hold unit for classifying and outputting an electrode offset voltage at a voltage, wherein the sample and hold unit samples an electrode voltage value output at the time of application of the input pulse when the input pulse is applied, The voltage value is fixedly output as the electrode offset voltage value in the stimulation period.

Description

Technical Field [0001] The present invention relates to a control of electrical offset voltage in an electrical stimulation system,

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric stimulation system capable of controlling an electrode offset voltage, and more particularly, to an electric stimulation system capable of adjusting an offset voltage of an electrode body that applies electric stimulation to a nerve or the like.

If the nerve is broken or damaged, the patient experiences a great inconvenience in life. To alleviate this inconvenience, an electric stimulation system is used to connect the electrode body to the nerve, to regenerate the nerve by applying electrical stimulation, or to generate a signal in place of the nerve signal.

The control of the electrode offset voltage is an important issue in the electrical stimulation process for the living body, since excessive charge accumulates in the electrode over time, damaging both the tissue and the electrode.

The electrode offset voltage refers to a voltage applied to an electrode body even though an input signal such as a stimulating current is not applied as the charge accumulates in the electrode body due to internal resistance or physical properties of the electrode body.

If the electrode offset voltage is constantly and excessively applied, electric charges may accumulate and fatigue may be given to the nerves to which the electrode body is attached. In addition, the electrode body is corroded by the accumulation of electric charges, which also affects the life of the electrode body.

Since bioelectrical stimulation is usually applied to the nerve on a periodic and continuous basis to effect the effect, it is necessary to continuously monitor and control the value of the electrode offset voltage to maintain or remove it to a desired level.

However, when a stimulating current is applied to the electrode body, a large peak-to-peak voltage is observed, and the offset voltage is difficult to measure by conventional filter technology, and it is more difficult to control the desired value to be.

Korean Patent Publication No. 10-2010-0089677

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide an electric stimulation system capable of continuously sensing an electrode offset voltage by charge accumulated in an electrode body, .

According to an aspect of the present invention, there is provided an electric stimulation system using an electrode body according to one aspect of the present invention includes an electrode body for applying a magnetic field current to a conductive medium, And a sample-and-hold unit for classifying and outputting an electrode offset voltage at an electrode voltage output from the electrode body, wherein the sample-and-hold unit comprises: And outputs the sampled electrode voltage value as the electrode offset voltage value in the stimulus period.

The electrical stimulation system may further include a controller for outputting a control signal for minimizing an error of the predetermined reference offset voltage and the electrode offset voltage, and the electrode offset voltage output from the sample and hold unit is supplied to the controller And the stimulating current generating unit generates the stimulating current reflecting the control signal and transmits the generated stimulating current to the electrode body.

The controller outputs a control voltage according to the control signal. The stimulus current generation unit includes a pulse generator for generating an input pulse, and a controller for converting the stimulus voltage obtained by combining the input pulse and the control voltage into the stimulus current, And a voltage-controlled current source that transmits the voltage to the electrode body.

Also, the input pulse may be applied with a pulse having a constant period, and the stimulus voltage and the stimulus current may be output as pulses having the same period as the input pulse.

Also, the pulse generator generates a sample and hold pulse synchronized with the input pulse and inputs the pulse to the sample-and-hold unit. The sample-and- And outputs the output electrode voltage as the electrode offset voltage.

Also, the input pulse may be generated as a two-phase pulse consisting of a negative pulse and a positive pulse, and the sample and hold pulse may be generated as a single-phase pulse.

The electrode body may include a working electrode to which the magnetic pole current is input, and a counter electrode to which the magnetic pole current is output.

Further, the surface area of the counter electrode may be the same as or similar to the surface area of the working electrode.

Further, the conductive medium is a biological nerve, and the electrode body may be attached to the nerve to transmit electrical stimulation to the nerve.

Also, the electrode body is modeled as a circuit model in which a Faraday impedance and a non-Faraday impedance are connected in parallel within the electrolyte, and the Faraday impedance and the non-Faraday impedance are pre-determined through electrolytic experiments similar to the biological environment of the organism It is possible.

In addition, the electrode body may be a cuff-shaped electrode body that is wound around the nerve to allow electrical stimulation to the surface.

The controller may also be a proportional integral controller.

Also, the control gain of the proportional-plus-integral controller may be determined by setting the transfer function of the sample-and-hold unit to 1.

In addition, the electrical stimulation system may further comprise a reference offset voltage generator capable of variably generating the reference offset voltage.

1 is a block diagram of an electrical stimulation system in accordance with an embodiment of the present invention.
2 shows an electrode body modeled by an electric circuit.
3 is a schematic view of an electrode body according to an embodiment of the present invention.
4 is a circuit diagram of a voltage-controlled current source according to an embodiment of the present invention.
5 is a circuit diagram of a sample-and-hold unit according to an embodiment of the present invention.
6 is a graph showing an example of a sample and hold operation using the sample and hold unit of FIG.
7 is a circuit diagram of a pulse generator according to an embodiment of the present invention.
FIG. 8 shows an example of pulse generation using the pulse generator of FIG.
9 is a circuit diagram of a reference offset voltage generator according to an embodiment of the present invention.
10 is a transfer function block diagram for the entire electrical stimulus sheath of FIG.
Figure 11 shows the pole-zero position of an open-loop transfer function for the design of a PI controller.
12 is a root-locus curve of characteristic equations for an example.
13 shows the unit step response and the output of the PI controller corresponding to the K value shown in Fig.
14 is a circuit diagram of a PI controller according to an embodiment of the present invention.
15 shows the response to an input pulse of two phases when the reference offset voltage is set to zero.
16 shows the response to the input pulse of two phases when a reference offset voltage other than 0 is set.
Figure 17 shows the response to a single phase input pulse when the reference offset voltage is set to zero.
18 is a graph for explaining the effect of the sample-and-hold unit.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. Although the present invention has been described with reference to the embodiments shown in the drawings, it is to be understood that the technical idea of the present invention and its essential structure and operation are not limited thereby.

1 is a block diagram of an electrical stimulation system 1 according to an embodiment of the present invention.

1, the electrical stimulation system (1), the electrode member 10 which is inserted into a living body is the stimulus current (I _stim), the input pulse stimulation current (I _stim) using the (P ^bb) It generates a classifying and outputting the stimulation current generation unit (20, 40) and the electrode member 10, the electrode offset voltage (V ^sh _offset) in the electrode voltage (V _e) to be output from the input to the electrode body (10) And a sample and hold (S / H) unit 30.

A reference offset voltage generator 50 for generating a reference offset voltage V ^ref _offset at a predetermined level and a reference voltage generator 50 for minimizing an error between a reference offset voltage V ^ref _offset and an electrode offset voltage V ^sh _offset And a controller (60) for outputting a control signal for controlling the motor.

The stimulus current generation units 20 and 40 include a pulse generator 40 that generates an input pulse ^{Pbb in the} form of a pulse and a voltage-controlled current source 20 that generates a stimulation current I _stim .

Hereinafter, each configuration of the electric stimulation system 1 according to the present embodiment will be described in detail.

Electrode body

The in vivo internal environment is a conductive electrolyte state. The electrode body 10 according to the present embodiment is inserted into the living body and attached to the nerve, and electric current is supplied to the nerve to electrically stimulate it.

The charge transfer at the electrode-electrolyte interface has two main mechanisms: non-Faradaic and faradaic reactions. The non-Felday reaction is a reaction that does not transfer electrons between the electrode and the electrolyte, causing redistribution of the charged chemical species inside the electrolyte. The Faraday reaction moves electrons between the electrode and the electrolyte, causing a reduction or oxidation of the chemical species inside the electrolyte.

Based on this mechanism, a simple electrical circuit model of the electrode-electrolyte interface is represented by a parallel connection of the non-ferrode capacitance and the Faraday resistance. As shown in FIG. 2, when the working electrode and the counter electrode are located in the electrolyte and the stimulation current I _stim passes between the electrodes through the electrolyte, a resistance of the electrolyte between the two electrode-electrolyte interfaces occurs.

Therefore, the transfer function of the electrode unit 10 is defined as a stimulation current (I _stim ) input and a corresponding Laplace transform of the electrode voltage (V _e ) output as shown in Equation (1) below.

[Equation 1]

Where R _Fw and R _Fc are the Faraday resistances of the working and counter electrodes, respectively, and C _nFw and C _{n Fc} are non-ferrode capacitors of the working and counter electrodes, respectively. R _s is the resistance of the electrolyte.

As shown in Fig. 3, according to the present embodiment, the electrode body 10 is a cuff-shaped electrode body wound around a living body nerve (not shown) so that the nerve can be electrically stimulated on its surface.

The cuff-shaped electrode body 10 is composed of a polyimide substrate 19 having ring-shaped platinum contact points. The two end contact points are shorted to serve as working electrodes 11 and 12 and the two center contact points are shorted to serve as the counter electrodes 13 and 14. [ The polyimide substrate 19 is configured to be dried inside, and can be wound around the outer surface of the nerve.

The four electrodes 11 to 14 are electrically connected to the connection pads 15 to 18, respectively. Depending on the phase of the input current pulse, current flows through the working electrode to the counter electrode via the nerve, the conductive medium.

Generally, the counter electrodes 13 and 14 have a large surface area. Therefore, it can be considered to have a large capacitance, and the influence on the electrode voltage can be neglected. However, the cuff-shaped electrode body 10 according to the present embodiment is formed such that the counter electrodes 13 and 14 have the same or similar cross-sectional area as the surface area of the working electrodes 11 and 12. Therefore, the effects of the counter electrodes 13 and 14 are included in the circuit model.

The Faraday impedance and the non-Faraday impedance of the working electrode and the counter electrode according to this embodiment can be determined by measuring the stimulation current applied in the electrolyte similar to the living environment in which the electrode body 10 is inserted and the electrode voltage corresponding thereto, do. Experiments have shown that the Faraday resistance and the non-Faraday capacitance of the working electrode are similar to the Faraday resistance and non-Faraday capacitance of the counter electrode.

Therefore, the transfer function G _e (S) of the electrode body 10 can be simplified as shown in the following equation (2).

&Quot; (2) "

Voltage-controlled Current source

According to the present embodiment, a voltage-controlled current source 20 is used to provide the stimulating current I _stim with the electrode body 10.

The voltage-controlled current source needs to have a significantly higher output impedance, and the output current error needs to be minimized over a wide range of excitation periods. To this end, according to the present embodiment, as shown in Fig. 4, a dual operation amplifier current source is used.

The circuit shown in Fig. 4 is based on the active feed-pack structure, so that the voltage _dropped through the resistor R _stim can be maintained at a constant value. The relationship between the stimulation voltage V _stim and the stimulation current I _stim is expressed by the following equation (3).

&Quot; (3) "

S / H unit

The main purpose of this specification is to provide a feedback control method for the charge balancing problem.

To configure the pad back loop, it is preferred that the electrode offset voltage be continuously monitored rather than intermittently.

According to this embodiment, a S / H method is proposed for sensing the electrode offset voltage.

Applied to the input pulse (P ^bb) are repeated is given by the two-phase (biphasic) pulse having a period, and the stimulus period is the S / H pulse synchronized single-phase pulse (P ^sh) the S / H unit 30) do. Then, the electrode voltage (V _e) is captured at the start of the S / H pulse (P ^sh), and is fixed to the end of the S / H pulse (P ^sh).

Referring to Figure 6 will be described again, S / H unit 30, the input pulse the electrode voltage (V _e) value output from the application time point of (P ^bb) the stimulation period, the input pulse (P ^bb) is input And the sampled electrode voltage (V _e ) value is fixedly output to the electrode offset voltage (or hereinafter, also referred to as "S / H offset voltage") V ^sh _offset in the stimulation period, In the non-magnetic period where the input pulse P ^bb is not input, the electrode voltage output from the electrode body is output as the electrode offset voltage value as it is. According to the above configuration, since the feedback control is maintained throughout the stimulation and non-stimulation periods, the change in the electrode offset voltage occurring during the stimulation period is negligible. As a result, the electrode offset voltage can be continuously sensed without interference of the stimulation current, regardless of the continuous stimulation.

As shown in FIG. 5, the S / H unit 30 is configured with analog switches and buffers. In sample mode, the switches are closed, and the output voltage depends on the input voltage. In the hold mode, the switches are opened and the input voltage is held by the hold capacitor C _h . Pedestal errors and hold time glitches are reduced by the compensating network of R _c and C _c .

Figure 6 shows an example of a sample and hold operation.

When the unbalanced two-phase current pulse is applied to the electrode body 10, the electrode voltage V _e does not disappear at the end of the single pulse, and the offset voltage gradually increases by the continuous pulse.

The electrode voltage (V _e ) is sampled and fixed according to the timing of the S / H pulse. As a result, the sample and hold electrode offset voltage (V ^sh _offset ) is given by Equation (4) below.

&Quot; (4) "

Here, k = 0, 1, 2, ..., t ₁ , t ₂ and T are the start point, end point and repetition period of the S / H pulse, respectively.

As will be described later, PI in the design process of the controller 60, the controller is used, it is a given by the step function based on the offset voltage (V ^ref _{offset _),} the voltage electrode unit a balanced two-phase input pulse (P ^bb) (Not shown). This is because the control purpose is to regulate the electrode offset voltage, not the electrode voltage V _e , and the balanced balancing two-phase pulse P ^bb is regarded as disturbance. In this situation, the electrode voltage (V _e) can be approximated as substantially electrode offset voltage (V _offset ^sh). Therefore, the transfer function of the S / H unit 30 can be expressed by the following equation (5).

&Quot; (5) "

Pulse generator

As described above, the input pulse ^Pbb as a two-phase pulse is composed of a negative pulse and a positive polarity pulse, and the S / H pulse has a single-phase waveform having the same width as the input pulse ^Pbb . These pulses are generated by a pulse generator 40 consisting of timers T and differential amplifiers as shown in Fig. The two timers T are formed in series to perform a monostable operation. Figure 8 shows an example of pulse generation.

A negative trigger pulse V _trig having a width smaller than the _cathodic pulse V _cathodic is generated by an external device (not shown) and applied to the pulse generator 40. The cathode pulse V _cathodic is generated from the falling edge of the trigger pulse V _trig and is coupled to the high pass filter. A bipolar pulse (V _anodic ) is generated from the falling edge of the output of the high pass filter. The widths of the positive electrode pulse and the negative electrode pulse are controlled by a combination of the resistor R _t and the capacitor C _{t as} shown in the following Equation (6).

&Quot; (6) "

The outputs from the timers T are subtracted by the subtracter and the inverted cathode pulses are added to the bipolar pulses. The output two-phase pulse (P ^bb ) is supplied through a voltage divider and a voltage follower for amplitude control.

Further, the S / H pulse P ^sh is generated by the same positive polarity pulse and negative polarity pulse used for the two-phase pulse P ^bb . The outputs from the timers T are added by the inverting synthesis amplifier, and their polarity is inverted by the inverting amplifier. This circuit allows the S / H pulse P ^sh to be synchronized to the two-phase pulse P ^bb .

Reference offset voltage generator

As shown in FIG. 9, the reference offset voltage generator 50 is configured using a voltage divider and a voltage follower. The reference offset voltage (V ^ref _offset ) is formed by setting the potentiometer.

By using the reference offset voltage generator 50 according to the circuit of Fig. 9, the generated reference offset voltage value can be varied by changing the position of the center tap of the potentiometer to change the resistance value.

For example, a reference offset voltage of 400 mV can be obtained by connecting VDD and VSS to 15 V and -15 V, R _offset to 10 kΩ, and the center tap of the potentiometer (POT _offset ) to VSS through a resistor of 10548 Ω.

Controller

1 is a controller 60. [0050] According to the present embodiment, the controller 60 uses a proportional integral (PI) controller.

The control target of the controller 60 is to cause the electrode offset voltage V ^sh _offset to follow a given reference offset voltage V ^ref _offset . Therefore, the error offset voltage V ^err _offset input to the controller 60 is expressed by the following equation (7).

&Quot; (7) "

The PI controller 60 generates a control signal proportional to a current error and an accumulated error according to time as expressed by Equation (8).

&Quot; (8) "

Where K _p and K _i are proportional gain and integral gain, respectively.

Thereafter, the excitation voltage V _stim is output as a composite value of the control voltage V _pi and the input pulse P ^bb , which are the outputs of the controller 60 as shown in the following equation (9).

&Quot; (9) "

As described above, in the designing process of the controller, it is assumed that the input pulse P ^bb is regarded as a disturbance and is not applied to the electrode body 10. Therefore, the stimulation voltage V _stim is the same as the output of the controller 60, and the transfer function of the controller 60 can be obtained as shown in the following equation (10).

&Quot; (10) "

Using the above equations (2), (3) and (5), the transfer function block diagram for the entire electric stimulation system 1 is shown in FIG.

As described above, since the transfer function of the sample-and-hold unit can be substantially set to 1, a closed-loop transfer function is derived as follows.

&Quot; (11) "

Here, the open loop transfer function is expressed by Equation (12).

&Quot; (12) "

In order to balance the charge on the electrode body 10, the reference offset voltage is usually given by a step function of arbitrary magnitude.

Assuming a unit step function, the specifications of the control performance are set as follows.

(1) Steady state error = 0

(2) Maximum overshoot ≤ 12%

(3) Rise time ≤ 1.5 ms

(4) Settling time ≤ 6 ms

(5) Maximum output of controller ≤ 1000μA

The immediate effect of the PI controller 60 is to add a pole to the open-loop transfer function at S = 0. If the reference offset voltage (V ^ref _offset ) is a unit step function, the steady state error is given by: " (13) "

&Quot; (13) "

The controller 60 reduces the steady-state error for the unit step function to zero. Thus, the design problem of the PI controller 60 is simplified by selecting the proportional and integral gains that satisfy the control performance specifications for the transient response and the controller output. Since the PI controller 60 is basically a low pass filter, the closed loop system always has a slower rise time and a longer settling time. However, if the position of zero, S = -K _i / K _p , is appropriately selected, the transient response characteristics can be improved. The root locus technique is proposed as a systematic way to design the PI controller 60.

The characteristic equation of the closed-loop system is obtained by setting the denominator polynomial of the transfer function to zero. Therefore, the root of the characteristic equation of the present system should satisfy the following expression (14).

&Quot; (14) "

The root of the characteristic equation corresponds to the pole of the closed-loop transfer function, and determines the stability and transient response of the closed-loop system. To evaluate the control characteristic with the PI gain, it is assumed that the open-loop transfer function has a variable parameter K as a multiplying factor. Therefore, the characteristic equation can be rewritten as Equation (15) below.

&Quot; (15) "

If K = 0 in Equation (15), the pole of the open loop transfer function becomes the root of the characteristic equation, and if K = ∞, it is clear that the zero of the open loop transfer function becomes the root of the characteristic equation. This root locus property is useful for understanding the control form of the closed loop system by selecting the appropriate PI gain and changing the parameter K from 0 to ∞.

All the roots of the characteristic equation should be located in the left plane of the S-plane in order to satisfy the stability of the linear control system. From the relationship between the characteristic equation and the open-loop transfer function, zero for S = -K _i / K _p should be chosen to be less than zero. Also, since the integral gain is inversely proportional to the capacitor value in the applied circuit, the integral gain should be chosen to be greater than the proportional gain.

To select the position of zero, the pole-zero position of the open loop transfer function is shown as in FIG. A possible area for locating the zero of the PI controller 60 is separated by the pole and zero position of the electrode body. The mathematical simulation results show that the zero located in Zone 1 provides an overdamped response in transient and the zero located in Zone 3 generates a large control output that exceeds the garden supply voltage. Therefore, the position of zero is selected in zone 2 and satisfies the following equation (16).

&Quot; (16) "

12 shows the root locus curve of the characteristic equation (15) when k _i = 2000 and k _p = 5 when K is changed from 0 to ∞.

Here, if the value of K is appropriately selected, the control characteristic can be improved. 13 shows the unit step response and output of the PI controller corresponding to the several K values shown in FIG. Referring to FIG. 13, it can be seen that as the value of K increases, the transient response is improved. On the other hand, a larger control output is required.

Fig. 14 shows the configuration of the PI controller 60 according to the present embodiment. The PI controller 60 is implemented using an inverting amplifier and an integrator, respectively, with proportional and integral terms. The negative gain of the proportional term and the integral term is inverted to positive gain by the inverting synthesis amplifier. The error offset voltage V ^err _offset is generated by the differential amplifier and the negative signal is removed by an additional differential amplifier used to ^{combine the} PI control output voltage V _pi with the input pulse P ^bb .

Therefore, the control voltage V _pi , which is the output of the PI controller 60, is given by the following equation (17).

&Quot; (17) "

Comparing Equations (8) and (17), it can be seen that the parameters of the PI controller are related to the parameters of the system as shown in the following Equation (18).

&Quot; (18) "

System behavior

Fig. 15 shows the response to a two-phase input pulse when the reference offset voltage V ^ref _offset is set to zero.

During the stimulation period, a stimulation voltage (V _stim ) of 0.5V is converted to a stimulation current (I _stim ) of 500μA. On the other hand, the entire stimulation period, and is not applied bijageuk period to which the stimulation current, S / H unit 30 can without interference of the stimulation current (I _stim) monitoring the electrode offset voltage (V ^sh _offset) have.

Although the two-phase pulse is designed to balance the charge, a small charge imbalance occurs in the pulse generated by the error of the electronic device. As a result, an offset voltage having a peak value of about 3.2 mV is observed at the output of the S / H circuit without the electrode voltage (V _e ) disappearing after each pulse ends. To compensate for this charge imbalance, the PI controller 60 generates a reversed phase control voltage which is negative converted to the stimulation current I _stim , and adjusts the offset voltage to 0 V during the non-stimulation period.

16 shows the response to the input pulse of two phases when a reference offset voltage other than 0 is set. During the initial period before the pulse is applied, the error between the reference value and the S / H offset voltage output from the S / H unit 30 is rapidly reduced by the PI controller 60.

In the present embodiment, the case where the input pulse is two-phase has been described, but it is not necessarily limited thereto. Fig. 17 shows the response to a single-phase input pulse when the reference offset voltage V ^ref _offset is set to zero. Referring to FIG. 17, it can be seen that the PI controller is converted into a positive excitation current portion to generate a reverse phase voltage acting as a positive pole pulse, thereby preventing accumulation of charges.

18 (a) shows a response to a 2-phase input pulse when the S / H unit 30 does not perform the S / H operation and the reference offset voltage is zero. Since the S / H operation is not performed, the output of the S / H unit 30 is the same as the electrode voltage V _e . During the stimulation period, the error offset voltage causes a significant peak-to-peak change, and the output of the corresponding controller affects the stimulation current. This effect has the effect of increasing the electrode voltage during the non-magnetic period, as compared to when the S / H operation is performed.

Since the depolarization and reverse electrochemical processes of neural membranes are related to the current applied, it is important that the stimulation current is constant throughout the pulse in the electrical stimulation system. As shown in Fig. 18 (b), the electrode voltage is fixed by the S / H unit 30 during the stimulation period, and the stimulation current is not affected by the output of the controller. Further, during the non-magnetic period, since the electrode voltage is directly output by the S / H unit 30, the value is rapidly controlled toward zero reference offset voltage.

According to the present embodiment, the sample and hold unit captures the electrode voltage value output at the time when the stimulus current is applied, for example, and detects the electrode voltage value as the electrode offset voltage value during application of the stimulus current So that it is possible to continuously monitor the electrode offset voltage without being interfered with the stimulation current.

The electrode offset voltage during the non-stimulation period is fed back to the PI controller, and the change in electrode offset voltage during the stimulation period can be ignored. Therefore, the system transfer function of the S / H unit can be set to 1, which simplifies the system in designing the control gain of the PI controller.

Since the electrode body according to this embodiment is based on the electrode-electrolyte model and the impedance value is determined through the preliminary experiment in the electrolytic solution, efforts for finding the parameters required for the design of the PI controller are greatly reduced.

Claims (15)

An electric stimulation system using an electrode body,
An electrode body for applying a stimulating current to the conductive medium;
A stimulating current generating unit that generates the stimulating current using an input pulse and inputs the generated stimulating current to the electrode body;
A sample and hold unit for classifying and outputting an electrode offset voltage at an electrode voltage output from the electrode body;
And a controller for outputting a control signal for minimizing an error of the predetermined reference offset voltage and the electrode offset voltage,
The sample and hold unit includes:
Wherein when the input pulse is applied, the electrode voltage value output at the application time of the input pulse is sampled, the sampled electrode voltage value is fixedly output as the electrode offset voltage value in the stimulus period,
The electrode offset voltage output from the sample and hold unit is fed back to the controller,
Wherein the stimulating current generating unit generates the stimulating current reflecting the control signal and transmits the generated stimulating current to the electrode body. delete The method according to claim 1,
The controller outputs a control voltage with the control signal,
The stimulus current generating unit includes:
A pulse generator for generating an input pulse;
And a voltage-controlled current source for converting a stimulation voltage obtained by synthesizing the input pulse and the control voltage into the stimulation current and delivering the stimulation current to the electrode body. The method of claim 3,
The input pulse is applied with a pulse of a constant period,
Wherein the stimulation voltage and the stimulation current are output in pulses having the same period as the input pulse. 5. The method of claim 4,
Wherein the pulse generator comprises:
A sample and hold pulse synchronized with the input pulse is generated and input to the sample and hold unit,
The sample and hold unit includes:
And outputs the electrode voltage output from the electrode body as the electrode offset voltage while the sample and hold pulse is not applied. 6. The method of claim 5,
Wherein the input pulse is generated as a two-phase pulse consisting of a negative pulse and a positive pulse. The method according to claim 6,
Wherein the sample and hold pulse is generated as a single phase pulse. The method according to claim 1,
Wherein the electrode body includes a working electrode to which the magnetic pole current is inputted and a counter electrode to which the magnetic pole current is outputted. 9. The method of claim 8,
Wherein the surface area of the counter electrode is the same as or similar to the surface area of the working electrode. 10. The method of claim 9,
The conductive medium is a nerve of the organism,
Wherein the electrode body is attached to the nerve to transmit an electrical stimulus to the nerve. 11. The method of claim 10,
The electrode body is modeled as a circuit model in which a Faraday impedance and a non-Faraday impedance are connected in parallel within the electrolyte,
Wherein the Faraday impedance and the non-Faraday impedance are predetermined through an electrolyte experiment similar to the biological environment of the organism. 11. The method of claim 10,
Wherein the electrode body is a cuff-shaped electrode wound around the nerve and capable of causing electrical stimulation to the surface of the nerve. The method according to claim 1,
Wherein the controller is a proportional integral controller. 14. The method of claim 13,
The control gain of the proportional-plus-
And the transfer function of the sample-and-hold unit is set to 1. The method according to claim 1,
Further comprising a reference offset voltage generator capable of variably generating the reference offset voltage.

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