KR20200107303A - Eeg sensing apparatus with feedback algorithm - Google Patents

Abstract

According to the present invention, provided is an EEG measurement device, which comprises: an instrument amplifier amplifying and outputting an EEG signal; a high band pass filter passing a high band at the output of the instrumentation amplifier; a fixed band charge-time converter receiving the output of the high band pass filter, and passing a low band for outputting the same as a digital signal; a variable band charge-time converter receiving the output of the high band pass filter and passing the low band for outputting the same as a digital signal; and an EEG analysis unit receiving the digital signal output from the fixed band charge-time converter and the variable band charge-time converter, calculating a relaxation index, and controlling a cutoff frequency of the variable band charge-time converter.

Description

EEG measurement device with feedback algorithm {EEG SENSING APPARATUS WITH FEEDBACK ALGORITHM}

The present technology relates to an EEG measurement device that can more clearly grasp the meditation state and the non-meditation state using a novel relaxation index.

EEG is the flow of electricity generated when signals are transmitted between the cranial nerves in the nervous system. It appears differently depending on the state of mind and body, and is the most important indicator for measuring the activity of the brain. EEG is recorded by attaching several electrodes on the scalp to record the sum of extracellular currents that occur due to the activity of cranial nerve cells, and is also called an electroencephalogram (EEG).

In the cognitive and memory performance that affects human thinking and behavior, the active area varies according to the work performed, and the pattern may change depending on age, individual ability, and the presence or absence of brain diseases.

Human brain waves can be classified as shown in Table 1 below. Various indicators can be obtained using the measured EEG, and among them, stability and stress can be determined by calculating the ratio of alpha to high beta power (RAHB) defined as Alpha / H-Beta.

In humans, H-Beta waves appear strong in a state of tension, excitement or stress, and alpha waves appear strong when mental and physical tensions are relaxed and stress is relieved. Considering these two characteristics, RAHB, which is the ratio of the alpha wave to the H-beta wave, is used as an indicator of relaxation (meditation, relaxation). RAHB indicators usually appear higher as the number of H-Beta waves that are activated during emotional anxiety decreases, and the more Alpha waves that are activated when the brain is resting or relaxing.

However, the conventional RAHB index has a disadvantage in that it is difficult to distinguish between meditation and non-meditation.

The present technology is to overcome the disadvantages of the prior art described above. That is, one of the major problems to be solved with this technology is to provide an EEG measurement device that can more clearly grasp the user's state by using a relaxation index that can more clearly indicate the distinction between meditation and screaming.

The EEG measurement device according to the present invention is provided with an instrument amplifier that amplifies and outputs an EEG signal, a high pass filter that passes a high pass from the output of the instrumentation amplifier, and an output of the high pass filter, and passes the low pass digitally. A fixed-band charge-time converter that outputs as a signal, a variable-band charge-time converter that receives the output of a high-pass filter, passes a low-pass, and outputs a digital signal, and a fixed-band charge-time converter and a variable-band charge-time converter are output. It includes an EEG analysis unit that receives a digital signal, calculates a relaxation index, and controls a cutoff frequency of the variable-band charge time converter.

를 연산하여 이완 지표를 구한다.(a, b:가중치, A: 알파파, H-beta: high 베타파, ATP(absolute total power): 절대 전체파의 파워)According to an embodiment of the present invention, the brain wave analysis unit, the equation

Calculate the relaxation index by calculating (a, b: weight, A: alpha wave, H-beta: high beta wave, ATP (absolute total power): absolute total power).

According to an embodiment of the present invention, the fixed band charge-time converter includes a first transconductance amplifier that outputs a current corresponding to a difference between an output voltage of a high-pass filter and a reference voltage, and a first A capacitor forming a first voltage corresponding to the output current of the transfer conductance amplifier, a comparator for comparing the first voltage and a threshold voltage of the comparator, a clock signal is provided as one input, and an output of the comparator is provided as the other input, And a counter for counting and outputting the number of clock signals corresponding to the output pulse width of the comparator.

According to an embodiment of the present invention, the variable band charge-time converter includes a second transfer conductor amplifier that outputs a current corresponding to a difference between an output voltage of a high-pass filter and a reference voltage, and a second transfer conductance amplifier. A capacitor bank forming a second voltage corresponding to the output current, a comparator for comparing the second voltage and the comparator threshold voltage, a clock signal is provided as one input, an output of the comparator is provided as the other input, and the output of the comparator It includes a counter that counts and outputs the number of clock signals corresponding to the pulse width.

According to an embodiment of the present invention, the comparator threshold voltage is a periodic signal, and includes a rising and falling period within one period.

According to an embodiment of the present invention, the EEG analysis unit controls at least one of the transfer conductance of the second transfer conductance amplifier and the capacitance of the capacitor bank to control the band of the variable-band charge-time converter.

According to one embodiment of the present invention, the capacitor bank includes a plurality of capacitors, and the variable band charge-time converter further includes a discharge switch for discharging charges charged in the plurality of capacitors included in the capacitor bank.

를 연산하여 집중력 지표를 더 구한다.(SMR: 12-15Hz의 SMR 베타파, M-beta: 15-20Hz의 M 베타파, Theta: 4-7 Hz 세타파)According to an embodiment of the present invention, the brain wave analysis unit, the equation

The concentration index is further calculated by calculating (SMR: SMR beta wave of 12-15 Hz, M-beta: M beta wave of 15-20 Hz, Theta: 4-7 Hz theta wave)

In one aspect of the present invention, the weights a and b are set differently according to the level of the user.

According to the present invention, it is possible to more clearly grasp the meditation state and the non-meditation state by using a novel relaxation index.

1 is a block diagram of an EEG measurement device according to the present invention.
2 is a diagram illustrating electrodes P1 and P2 arranged according to the international 10-20 system.
3 is a schematic circuit diagram of an instrumentation amplifier 100.
4 shows an overview of a fixed band charge-time converter.
5(A) is a timing diagram of a charge-time converter according to the prior art, and FIG. 5(B) is a schematic timing diagram of a charge-time converter according to the present invention.
6 shows an overview of a variable band charge-time converter.
7 is an exemplary diagram showing an outline of a capacitor bank (C _bank ).
8(A) FIGS. 8(B) and 8(C) are diagrams showing brain waves acquired by beginners, a conventional RAHB index, and a relaxation index according to the present invention.
9(A), 9(B), and 9(C) are diagrams showing brain waves acquired by an intermediate person, a conventional RAHB index, and a relaxation index according to the present invention.
10(A), 10(B) and 10(C) are diagrams showing brain waves acquired by advanced users, a conventional RAHB index, and a relaxation index according to the present invention.

Hereinafter, an EEG measurement apparatus according to the present invention will be described with reference to the accompanying drawings.

1 is a block diagram of an EEG measurement apparatus according to the present invention. Referring to FIG. 1, the EEG measurement apparatus according to the present invention includes an instrumentation amplifier 100 for amplifying and outputting an EEG signal, a high pass filter 200 for passing a high pass at the output of the instrumentation amplifier, and a high pass. A fixed-band charge-time converter 310 that receives the output of the filter 200, passes a low pass, and outputs a digital signal, and a variable that receives the output of the high pass filter 200 and passes the low pass to output a digital signal. It includes a band charge time converter 320 and an EEG analysis unit 400 that receives a digital signal, calculates a relaxation index, and controls a cutoff frequency of the variable band charge time converter.

EEG signals are generally measured on the scalp and are detected from electrodes P1 and P2 arranged according to the international 10-20 system as illustrated in FIG. 2. "10" and "20" mean that the actual distance between adjacent electrodes is 10% or 20% of the total anterior-posterior or left-right distance of the skull. As an example, measurements are made across the head from the nasal point (鼻根點, nasion) to the apex of the external laryngeal ridge (外後頭隆起頂點, inion).

The EEG measured on the scalp has a frequency of about 1-60Hz and a voltage of 5-300μV. For example, a typical alpha wave and a beta wave have voltages of approximately 50 μV and 20 μV, respectively. The EEG signals measured by the electrodes P1 and P2 are provided to an instrumentation amplifier 100.

In general, the EEG measurement system amplifies and uses a minute human signal 1,000 times or more, and due to the characteristic of using the frequency component of the signal, it is possible to accurately measure and analyze EEG if it has a certain degree of amplification within a desired band.

In the conventional EEG measurement system, a comparator, a high pass filter, a low pass filter, and an analog-to-digital converter (ADC) were provided, but the EEG signal was analyzed by using the EEG signal passed through the analog-to-digital converter. .

However, since the conventional EEG measurement system has a structure in which the cutoff frequency of a low pass filter (LPF) is determined by an external resistor and a capacitor, detailed monitoring through EEG analysis is required. There was a disadvantage in that it was impossible to control the cutoff frequency.

Therefore, the present invention eliminates the low-pass filter in the conventional EEG measurement system, and as shown in FIG. 1, the fixed-band charge-time converter 310 and the variable-band charge-time converter in parallel to the high-pass filter 200 It connects 320 and connects the fixed-band charge-time converter 310 and the variable-band charge-time converter 320 to the EEG analysis unit 400.

In the end, if the above structure is taken, the EEG signal output from the fixed-band charge-time converter 310 is input to the EEG analysis unit 400 to be used for EEG analysis, and as a result of EEG analysis, it is required according to the current EEG state. Cutoff frequency control through the variable-band charge-time converter 320 is performed by the EEG analysis unit 400 so that a signal within a specific band can be monitored in detail.

As described above, the present invention monitors the entire band of the EEG input from the fixed-band charge-time converter 310 and simultaneously monitors a specific band that is to be monitored in more detail. Analysis and extraction are more obvious advantages.

3 is a schematic circuit diagram of the instrumentation amplifier 100. Referring to FIG. 3, the instrumentation amplifier 100 removes noise components from the EEG signals detected and output by the electrodes P1 and P2 and amplifies and outputs the EEG signals.

In the EEG signals provided by the electrodes P1 and P2, not only the EEG signal, which is a differential mode signal, but also a noise component, which is a common mode, is present. Since the instrumentation amplifier 100 has a high common mode rejection ratio (CMRR), noise, which is a common mode component, can be removed. In addition, since it has a high input impedance, it is possible to reduce an error caused by a detection signal non-uniformity caused by an impedance mismatch between electrodes.

According to an embodiment not shown, the instrumentation amplifier 100 further includes a negative feedback path, and a low pass filter (LPF) may be disposed in the negative feedback path. As a result, the instrumentation amplifier 100 may have a high pass characteristic as a whole, and may remove a DC offset voltage generated by resistance at the contact surface of the body skin and the electrode.

Referring back to FIG. 1, the high-pass filter 200 is configured to exclude a frequency component below a cut-off frequency, and passes a biosignal in a frequency band higher than the cut-off frequency among signals output from the instrumentation amplifier.

The high-pass filter 200 may be implemented as a first-order or second-order or higher-order RC filter, for example, and is independent of types such as an active filter and a passive filter. In addition, it may be implemented with various types of filters such as a Bessel filter, a Butterworth filter, or a Chebyshev filter.

4 is a schematic diagram of a fixed band charge-time converter 310. 4, the fixed-band charge-time converter 310 receives an EEG signal V _IN and a reference voltage V _RLD that have passed through the high-pass filter 200 and receives a current corresponding to the difference (I _OTA). A first trans-conductance amplifier 312 outputting ), a capacitor C forming a first voltage corresponding to the output current of the first transfer conductance amplifier, and a first voltage and a reference voltage Comparator 316 to compare, a clock signal (CLK) is provided as one input, the output of the comparator is provided as another input, and a counter 318 that counts and outputs the number of clock signals corresponding to the output pulse width of the comparator. ).

The first transfer conductance amplifier 312 receives the EEG signal V _IN and the reference voltage V _RLD passed through the high pass filter 200 and outputs a current I _OTA corresponding to the difference. The output current I _OTA of the transfer conductance amplifier can be expressed as Equation 1 below.

gm: transfer conductance of the amplifier

The transfer conductance gm may have a fixed value as a characteristic value of the amplifier, and may be controlled according to a signal provided from the outside.

The current I _OTA output from the transfer conductance amplifier 312 is provided to the capacitor C, and the capacitor C accumulates the current I _OTA to the output node of the corresponding transfer conductance amplifier 312 below. A voltage V _{OTA_OUT} represented by Equation 2 is formed.

The comparator 316 compares the voltage (V _{OTA_OUT} ) formed at the output node of the transfer conductance amplifier 312 provided as one input and the comparator threshold voltage (V _REFT ) output from the threshold voltage generator 314 provided as another input. And outputs a pulse corresponding to the size. In the embodiment illustrated in FIG. 4, when the voltage V _{OTA_OUT} formed at the output node of the transfer conductance amplifier 312 is greater than the comparator threshold voltage V _REFT , a logic high state is output, and the transfer conductance amplifier 312 is When the voltage V _{OTA_OUT} formed at the output node is less than the comparator threshold voltage V _REFT , a logic low state is output.

The discharge switch is periodically provided with a reset signal RST to discharge the charge charged in the capacitor C. Accordingly, the voltage formed at the output node of the transfer conductance amplifier 312 is periodically reset.

Therefore, the comparator 316 is periodically reset, and the voltage (V _{OTA_OUT} ) formed at the output node of the transfer conductance amplifier 312 has a duty ratio according to the magnitude between the comparator threshold voltage (V _REFT ). Outputs a pulse (OUT).

5(A) is a timing diagram of a charge-time converter according to the prior art, and FIG. 5(B) is a schematic timing diagram of a charge-time converter 310 according to the present invention.

4 and 5A, the charge-time converter 310 according to the prior art does not change the level of the comparator threshold voltage V _RLD . Accordingly, there may be a case where a biosignal is transmitted to the transfer conductance amplifier to form a voltage at the output node of the transfer conductance amplifier, but the magnitude may not reach the comparison voltage. In this case, the EEG signal is generated as shown by the broken line in FIG. 5A, but it is measured that the EEG signal is not generated in the EEG signal measurement system.

Referring to the timing diagram of this embodiment illustrated in FIG. 5(B) and FIG. 4, the threshold voltage generator 314 according to the present embodiment generates a comparator threshold voltage V _REFT including a rising section and a falling section for one period. Form and output. Accordingly, the charge time converter according to the prior art can measure the part where the EEG signal has not been measured, and accordingly, it is possible to grasp the formation of the pulse signal OUT.

A clock signal is input to the counter 318 as an input, and a pulse signal OUT output from the comparator 316 is provided as the other input. In one embodiment, the counter 318 counts the number of pulses included in the clock signal CLK during the logic high state of the pulse signal OUT, and outputs a corresponding digital code. The higher the frequency of the clock signal CLK provided to the counter 318, the higher the resolution digital code can be obtained.

6 is a schematic diagram of a variable band charge-time converter 320. 6, the variable band charge-time converter 320 receives the EEG signal (V _IN ) and the reference voltage (V _RLD ) that have passed through the high-pass filter 200, and receives a current corresponding to the difference (I _OTA). A second transfer conductance amplifier 322 outputting ), a capacitor bank Cbank forming a second voltage corresponding to the output current of the second transfer conductance amplifier 322, and a first voltage and a reference voltage are compared A comparator 326 is provided, a clock signal CLK is provided as one input, an output of the comparator OUT is provided as another input, and a counter that counts and outputs the number of clock signals corresponding to the output pulse width of the comparator ( 328).

In describing the variable-band charge-time converter 320, descriptions of elements that are the same as or similar to the fixed-band charge-time converter 320 described above may be omitted. The output current I _OTA of the second transfer conductance amplifier 322 may be provided to the capacitor bank C _bank . A capacitor bank (C _bank ) is a plurality of capacitors (C1, C2, C3, ..., Cn) are connected in parallel as illustrated in Figure 7, the capacitors (C1, C2, C3, ..., One electrode of Cn) may be connected to each switch. The switches may be turned on or off by a capacitor control signal Ccont provided by the EEG analysis unit 400.

The EEG analysis unit 400 may control the capacitor bank Cbank to have a desired equivalent capacitance by outputting the capacitor control signal Ccont. In addition, the EEG analysis unit 400 may control the transfer conductance by providing a transfer conductance control signal to the transfer conductance amplifier.

The EEG analysis unit 400 adjusts the transfer conductance gm value of the second transfer conductance amplifier 320 included in the variable band charge-time converter 320 and the equivalent capacitance value of the capacitor bank Cbank to adjust the low-frequency cutoff frequency. (Low-pass cutoff frequency) can be controlled.

The EEG analysis unit 400 receives a digital signal from the fixed band charge-time converter 310 and the variable band charge-time converter 320 and calculates a relaxation index. The relaxation index according to the present embodiment may be calculated as in Equation 3 below.

In one embodiment, the weights a and b may be differently determined according to a beginner, intermediate, and advanced meditation.

In an embodiment, the EEG analysis unit 400 may receive a digital signal from the fixed-band charge-time converter 310 and the variable-band charge-time converter 320 and calculate a concentration index. The concentration index may be calculated as in Equation 4 below.

(SMR: SMR beta wave of 12-15Hz, M-beta: M beta wave of 15-20Hz, Theta: 4-7 Hz Theta wave)

The EEG analysis unit 400 outputs a capacitor control signal Ccont so that a signal within a required band according to the current state can be monitored in detail from the relaxation index obtained by analyzing the EEG signal, and the variable band charge-time converter 320 The cutoff frequency can be adjusted.

Experimental example

The following tests were performed on test subjects, including beginners, intermediate and advanced students. The time and steps of the test are as follows.

Preparation (22-30 seconds): Steps describing the test procedure

Sky image (20 seconds): preparing for the next step

Target image (1 min): focus stage

Sky image (20 seconds): preparing for the next step

Valley image (1 min): steps to meditate

Sky image: steps to prepare for the next step

8(A) FIGS. 8(B) and 8(C) are diagrams showing brain waves acquired by beginners in the test performed as above, a conventional RAHB indicator, and a relaxation indicator according to the present invention, and FIG. 9(A) ), Figures 9(B) and 9(C) are diagrams showing brain waves acquired by intermediates, conventional RAHB indicators, and relaxation indicators according to the present invention, and FIGS. 10(A), 10(B) and FIG. Fig. 10(C) is a diagram showing an EEG acquired by an advanced person, a conventional RAHB index, and a relaxation index according to the present invention. In each drawing, the meditation state is indicated by a bold square.

Referring to Fig. 8(A) showing the brain waves acquired by the beginner and the conventional RAHB indicator obtained therefrom, the preparation stage and the meditation stage are not generally distinguished, and the phenomenon that the meditation stage is lower than the preparation stage occurs. Can be confirmed. However, referring to FIG. 8(C), which shows the relaxation index according to the present invention to which the weights (a, b) for beginners are applied, it can be seen that the relaxation index comes out higher in the meditation stage than in the preparation stage.

Referring to FIG. 9(A) showing the brain waves acquired by the intermediate person and the conventional RAHB index obtained therefrom, it can be seen that the preparatory stage and the meditation stage can be classified as a whole, but there is no significant difference. However, referring to FIG. 9(C) showing the relaxation index according to the present invention to which the weights (a, b) for the intermediate class are applied, it can be seen that the relaxation index in the meditation stage is formed with a larger difference than the preparation stage. .

Referring to FIG. 10(A) showing the brain waves acquired by the advanced person and the conventional RAHB index obtained therefrom, it can be seen that there are cases in which the RAHB index is higher in the preparation stage than in the meditation stage. However, referring to FIG. 10(C) showing the relaxation index according to the present invention to which the weights (a, b) for advanced persons are applied, it can be seen that the relaxation index in the meditation step differs by a greater extent than any other state. have.

In the above experimental results, the EEG obtained by adjusting the bandwidth of the variable-band charge-time converter according to the present invention and the relaxation index according to the present invention in which the weights are set differently according to the level of beginner, intermediate and advanced obtained therefrom. If used, it can be seen that the distinction between screaming and meditation can be more clearly expressed.

100: instrumentation amplifier
200: high pass filter
310: Fixed band charge-time converter
312: first transfer conductance amplifier
314: threshold voltage generator
316: comparator
318: counter
320: variable band charge-time converter
322: second transfer conductance amplifier
324: threshold voltage generator
326: comparator
400: brain wave analysis unit
Cbank: capacitor bank

Claims (5)

An instrumentation amplifier for amplifying and outputting an EEG signal;
A high pass filter for passing a high pass at the output of the instrumentation amplifier;
A fixed-band charge-time converter that receives the output of the high-pass filter, passes a low pass, and outputs a digital signal;
A variable-band charge time converter receiving the output of the high-pass filter, passing a low pass, and outputting a digital signal; And
Including; an EEG analysis unit receiving the digital signal output from the fixed-band charge-time converter and the variable-band charge-time converter, calculating a relaxation index, and controlling a cutoff frequency of the variable-band charge-time converter;
The EEG analysis unit,
Equation

EEG measurement device, characterized in that to calculate the relaxation index to obtain.
(a, b: weight, A: alpha wave, H-beta: high beta wave, ATP (absolute total power): absolute total power)
The method of claim 1,
The EEG analysis unit,
Equation

EEG measurement device, characterized in that the concentration index is further calculated by calculating (SMR: SMR beta wave of 12-15 Hz, M-beta: M beta wave of 15-20 Hz, Theta: 4-7 Hz theta wave)
The method of claim 1,
The a, b weights,
EEG measurement device, characterized in that it is set differently according to the level of the user.
The method of claim 1, wherein the fixed band charge-time converter,
A first transconductance amplifier outputting a current corresponding to a difference between the output voltage of the high-pass filter and a reference voltage;
A capacitor forming a first voltage corresponding to the output current of the first transfer conductance amplifier;
A comparator for comparing the first voltage and a comparator threshold voltage; And
A counter for providing a clock signal as an input, an output of the comparator as another input, and counting and outputting the number of clock signals corresponding to the output pulse width of the comparator;
EEG measuring device comprising a.
The method of claim 1, wherein the variable band charge-time converter,
A second transfer conductor amplifier outputting a current corresponding to a difference between the output voltage of the high-pass filter and a reference voltage;
A capacitor bank forming a second voltage corresponding to the output current of the second transfer conductance amplifier;
A comparator for comparing the second voltage and a comparator threshold voltage; And
A counter for providing a clock signal as an input, an output of the comparator as another input, and counting and outputting the number of clock signals corresponding to the output pulse width of the comparator;
EEG measuring device comprising a.

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