KR20180018922A - Improved bio-potential measurement system - Google Patents

Abstract

The present invention relates to a system for measuring a biosignal and, more specifically, to an improved biosignal measurement system which uses a charge-to-time converter (QTC) unit including an operational transconductance amplifier (OTA) and a comparator in biosignal measurement and allows a comparison voltage inputted into the comparator to have an increasing section and a decreasing section to go through all voltages within a set range during a single period to obtain a comparator output similar to a normal condition even in various abnormal conditions. The improved biosignal measurement system comprises: an amplification unit to receive a biosignal to amplify the biosignal; a high pass filter (HPF) unit to allow a frequency band biosignal of a set frequency or higher in the amplified biosignal to pass therethrough; and a QTC unit to perform signal processing on the biosignal passing through the high pass filter unit to output a biosignal measurement result. The QTC unit comprises: an OTA to receive the biosignal passing through the high pass filter unit and a reference voltage to discharge an output current incorporating a difference therebetween; a comparator to compare an output end voltage of the OTA and a comparison voltage to output a result value; and a comparison voltage generator to generate a comparison voltage having an increasing section and a decreasing section to go through all voltages within a set range during a single period to input the comparison voltage into the comparator.

Description

[0001] IMPROVED BIO-POTENTIAL MEASUREMENT SYSTEM [0002]

The present invention relates to a system for measuring a biological signal, and more particularly, to a system for measuring a biological signal, more particularly, a QTC unit including an OTA and a comparator, The present invention relates to an improved bio-signal measuring system for obtaining a comparator output approximate to that of a normal condition under various non-normal conditions by having a rising section and a falling section.

Generally, an analog front-end of a bio-signal measurement system capable of measuring electro-encephalogram (EEG), electrocardiogram (ECG) and electromyogram (EMG) -End: AFE) The chip circuit can be composed of an initial amplifier stage and a band-pass filter stage capable of band adjustment, and a stage of a variable gain amplifier stage and an AD converter.

Each biomedical signal has slightly different signal magnitudes and frequency bands. The EEG signal exists in the frequency band of about 0.3 Hz to 100 Hz and has a voltage magnitude of about 1 kV to about 100 kV. The electrocardiogram signal exists in the frequency band of about 0.3 Hz to 350 Hz and has a voltage magnitude of about 100 kV to 10 kV. The electromyogram signal exists in the frequency band of about 20 Hz to 1000 Hz (= 1 kHz) and has a frequency characteristic somewhat higher than that of other living body signals. However, the voltage magnitude has a characteristic smaller than that of the electrocardiogram signal of about 80 kV to 1 kV.

Therefore, in order to select a frequency bandwidth suited to each bio-signal characteristic, a band-pass filter stage should be able to perform a bandwidth control function. In general, a band-pass filter is configured by connecting a high-pass filter and a low-

In order to pass only a specific frequency band signal, the low pass cutoff frequency and the high pass cutoff frequency are adjusted. As described above, since the bio-signal corresponds to a relatively low frequency band, the band- Pass cutoff frequency.

The low-pass cut-off frequency is characterized in that it varies depending on the value of the resistance (R) and the capacitance (C). In order to have the low-pass cutoff frequency of several tens of Hz, a considerably large resistance value and a large capacitance value are required. The device having a resistance value and a capacitance value for implementing the low-pass cutoff frequency of the AD converter has a size that can not be integrated into one chip circuit. have.

In addition, ECG and EMG of 8-bits to 10-bits and electroencephalograms of 12-bits or more require a high-resolution AD converter unit due to the nature of biological signals, but it is technically difficult to implement such AD converter units in integrated chip circuits And the voltage at the sampling time point is converted into a digit code due to the characteristic of the currently applied AD converter stage, so that there is a section where the biological signal is not reflected.

Meanwhile, in the present invention, a QTC unit including OTA and a comparator is used for measuring a bio-signal. In this case, if the difference between the reference voltage and the bio-signal input to the OTA is very small, the conductance (gm) Or when the value of the capacitor (C) connected to the OTA output terminal is considerably large, the OTA output voltage does not reach the comparative voltage inputted to the comparator, There is a problem.

Therefore, there is a need for a bio-signal measurement system capable of performing the bio-signal measurement more clearly and efficiently by solving the above-mentioned disadvantages and problems.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional art described above, and it is an object of the present invention to provide a filter stage capable of adjusting a low-pass cut-off frequency without necessarily using an element having a resistance value and a capacitance value large enough not to be integrated It is an object of the present invention to implement a bio-signal measurement system in one analog front-end chip circuit.

Further, in the bio-signal measurement of the bio-signal measurement system, the comparison voltage inputted to the comparator is not maintained at a constant level but is configured to include the rising section and the falling section so that the bio-signal measurement can be performed in all sections There is another purpose.

The technical objects to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical subjects which are not mentioned can be clearly understood by those skilled in the art from the description of the present invention .

According to an aspect of the present invention, there is provided a biometric authentication system comprising: an amplification unit for receiving and amplifying a bio-signal; a high pass filter (HPF) for passing only a bi- And a QTC (charge-to-time converter) unit for signal processing the bio-signal passing through the high-pass filter unit to output a bio-signal measurement result, wherein the QTC unit comprises: a bi- A comparator for comparing the output voltage of the OTA with a comparison voltage and outputting a result value, and a comparator for comparing the output voltage of the OTA with the output voltage of the rising section And a comparison voltage generator for generating a comparison voltage having a falling period and inputting the comparison voltage to the comparator. It provides an improved bio-signal measurement system, characterized in that.

In the present invention, the QTC unit may adjust the low pass cutoff frequency by adjusting at least one of the conductance (gm) of the OTA or the capacitance (C) of the capacitor connected to the output terminal of the OTA.

In the present invention, the QTC unit may further include a counter capable of counting a result value output from the comparator for a predetermined period.

In the present invention, it is preferable that the amplification unit uses an instrument amplifier.

In the present invention, the high-pass filter unit may use at least one of a Bessel filter, a Butterworth filter, and a Chebyshev filter.

The present invention enables the bio-signal measurement system to be implemented in one analog front-end chip circuit without using a resistor or a capacitor having a large value by using a QTC unit including OTA and a comparator.

Further, according to the present invention, the A / D converter stage is implemented with a high resolution and the comparison voltage input to the comparator is configured to have a rising section and a falling section instead of a constant level, thereby minimizing a portion missing in the measurement in the bio- There is an effect that a biological signal can be measured.

1 is a block diagram of an improved bio-signal measurement system according to an embodiment of the present invention;
BACKGROUND OF THE INVENTION 1. Field of the Invention [0001]
3 is an exemplary view showing a structure of a QTC unit according to an embodiment of the present invention.
FIG. 4 is an exemplary diagram showing the input and output of each configuration of the QTC subtractor when the comparison voltage is at a constant level; FIG.
FIG. 5 is an exemplary view showing the input and output of each configuration of the QTC subtractor when the comparison voltage has a rising section and a falling section; FIG.
6 is an exemplary diagram illustrating an output according to an input signal of a QTC unit according to an embodiment of the present invention.
FIG. 7 is a diagram illustrating an output of a conventional AD converter stage and an output of a QTC section according to an embodiment of the present invention; FIG.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor can properly define the concept of a term to describe its invention in the best possible way It should be construed as meaning and concept consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely the most preferred embodiments of the present invention, and not all of the technical ideas of the present invention are described. Therefore, It is to be understood that equivalents and modifications are possible.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an", and "the" include plural referents unless the context clearly dictates otherwise.

Before describing the present invention, brief description will be given of biological signals. A biological signal is one of the electric phenomena of an organism. The source of dislocation formed on the surface of the skin includes ions passing through a cell membrane in a neuron, . ≪ / RTI >

Because the nerve tissue is surrounded by the conductive medium, the electric current generated in the nerve tissue is formed on the surface of the skin, so that the electric potential is represented. The biological signal generated by the brain activity is divided into the action current and action potential The electrocardiogram and the vital signal generated by the movement of the muscles are called the EMG.

Such biological signals or bioelectrical signals are generated by a potential difference existing inside and outside the cell membrane, which is caused by the characteristics of a cell membrane that distinguishes intercellular fluid and extracellular fluid.

Since the tissues and body fluids of the living body have electrical conductivity, current flows around the activated cells. In vivo, the information transmission is caused by the action potential generated by excitation stimulation being transmitted through the nerve, Stimulation of the cell of the site, and when the excitation intensity is greater than the action potential threshold, a new action potential is generated and transmitted to the adjacent cell.

As described above, the bio-signals are characterized by having a specific frequency band and a specific voltage magnitude. All of the bio-signals are analog electrical signals, and most of them have low power / high noise ratio / fine signal characteristics. Therefore, It requires processing.

In order to integrate the bio-signal measurement system for measuring the bio-signal of the above characteristics into one analog front-end chip circuit and to minimize the missing part of the bio-signal measurement, The present invention relates to a biosensor comprising: an amplifying part for receiving and amplifying a bio-signal; a high pass filter (HPF) part for passing only a frequency band biomedical signal of a predetermined frequency or higher among the amplified bio- And a QTC (charge-to-time converter) unit for outputting a bio-signal measurement result by signal processing the QTC unit. The QTC unit receives the bio-signal and the reference voltage passed through the high-pass filter unit, The operational transconductance amplifier (OTA) compares the output voltage of the OTA with the comparison voltage Generating a comparison result to the voltage comparator and a voltage value within a predetermined range and outputting the value that has the rising period and the falling period to go through all for a period characterized by including a comparison voltage generator for input to the comparator.

1 is a block diagram of an improved bio-signal measurement system according to an embodiment of the present invention.

First, the amplifying unit 100 of the present invention is configured to receive and amplify a living body signal. In order to remove the influence of noise in the measurement of a living body signal and extract only a desired signal component, a differential amplifier may be used. When input signals with high common mode rejection ratio (CMRR) are low due to low input impedance, there is a high possibility that distortion occurs. When the input signal and the output terminal are input, and between the input signal and the ground terminal There is a disadvantage that the power supply is not completely separated.

Therefore, it is preferable that the amplifier 100 uses an instrument amplifier whose input impedance is relatively higher than that of the differential amplifier.

FIG. 2 illustrates an exemplary structure of a measurement amplifier according to an embodiment of the present invention. The instrumentation amplifier is a circuit in which the input impedance is increased while maintaining the common mode rejection ratio characteristic of the differential amplifier. Like the configuration shown in the drawing, the instrumentation amplifier has two operational amplifiers having two inputs and a common output separated from the output stage and the ground stage As shown in FIG.

Since the two amplifiers have the same gain and opposite phases, the ideal output value should be 0 when the same signal is input to both inputs, and the ability to cancel the same signal is called the common mode rejection ratio The common mode rejection ratio corresponds to about 1,000,000: 1 (60dB)).

The output voltage of the measurement amplifier shown in the figure can be expressed by the following equation.

V _out = (V ₂ - V ₁ ) * (1 + 2R ₁ / R _G ) * (R ₃ / R ₂ ) + V _ref

Generally, in a measurement amplifier circuit using a sensor, noise components are mixed with the same phase component at two input terminals. Therefore, a measurement amplifier is used to remove the noise component. If the impedance of the electrode is not the same, The common mode rejection efficiency is lowered because the size of the applied signal is not the same. Therefore, in order to overcome the error of the electrode impedance, the input impedance of the amplifier must be made very large.

In other words, the amplification unit 100 of the present invention using the instrumentation amplifiers can be configured to: 1) have a high impedance for receiving a low-level input signal without distortion; 2) amplify the biological AC signal sufficiently 3) low noise, and 4) AC-coupling for eliminating DC offset voltage caused by resistance on body skin and electrode contacts.

When AC-coupling is implemented with a low-pass filter in the feedback loop of the amplifier, the entire transfer function will have the characteristics of a high-pass filter, thereby eliminating the DC offset voltage. In order to maintain a cut-off frequency of several Hz in terms of the characteristics of a biological signal, a large resistance value and a large capacitance value are required. For example, when the resistance value is 1 MΩ and the capacitance value is 0.1Ω, Signals with frequencies below 1.59 Hz are rejected.

The high-pass filter unit 200 according to the present invention filters a bio-signal component having a frequency equal to or lower than a cut-off frequency, and conversely corresponds to a configuration in which only a bio-signal of a frequency band exceeding a predetermined frequency is passed among the bio- .

Various types of filter circuits can be used, such as a Bessel filter, a Butterworth filter, or a Chebyshev filter. To achieve the desired result, adjust the filter circuit type, resistance value, or capacitance value. .

In addition, the QTC unit 300 of the present invention has a configuration in which a bio-signal that has passed through the high-pass filter unit 200 is subjected to signal processing through an internal configuration to output a bio-signal measurement result. An example showing the structure of the QTC unit according to the example is shown.

As shown in the figure, the QTC unit 300 receives an in-vivo signal V _IN and a reference voltage V _RLD that have passed through the high-pass filter unit 200 and outputs an output current I _OTA reflecting the difference And a comparator 320 for comparing the output voltage V _{OTA_OUT} of the OTA with a comparison voltage V _REFT and outputting a resultant value.

Here, when the comparison voltage has a constant level, the output of the comparator becomes high (H) when the comparison voltage is reached depending on whether the OTA output voltage reaches the comparison voltage or the output of the comparator is low (L).

However, if a bio-signal is transmitted to the OTA but the OTA output voltage does not reach the comparison voltage, the bio-signal is generated, but the bio-signal measurement system measures the bio-signal as being not generated.

Accordingly, the present invention further includes a comparison voltage generator 330 for generating a comparison voltage having a rising section and a falling section so as to pass the voltage value within a predetermined range for one period, and inputting the comparison voltage to the comparator.

In order to assist in the explanation, FIG. 4 shows an example of input and output of the QTC auxiliary configuration when the comparison voltage is at a constant level, and FIG. 5 shows an example of the input and output of the QTC auxiliary configuration when the comparison voltage has a rising period and a falling period. An example of input and output of each configuration is shown.

In FIG. 4, the blue signal indicates that the OTA output voltage is generated but the reference voltage of a certain level can not be reached, so that the output of the comparator becomes low.

However, when the comparison voltage having the rising section and the falling section is input to the comparator as shown in FIG. 5, the OTA output voltage always reaches the comparison voltage according to the generation of the bio-signal, so that even when the reference voltage has a constant level, The problem that can not be solved is solved.

When the comparison voltage of the waveform shown in FIG. 5 is inputted, when the same OTA output terminal voltage is formed to be smaller than the comparison voltage, the OTA output terminal voltage may not reach the comparison voltage, but this is only an embodiment of the present invention If the configuration of the comparison voltage is configured to match the characteristics of the bio-signal, the above problem will be solved. It is needless to say that the comparison voltage may be configured so as to have a plurality of rising and falling periods within one cycle as needed.

In addition, the voltage value within the set range can be appropriately adjusted according to the size of the bio-signal and the internal parameters of the OTA 310. The type and size of the bio-signal generated by the OTA 310 can be determined by the characteristics of the rising section and the falling section Distribution within the period, etc.).

Meanwhile, a capacitor C and a reset switch RST are disposed between the output terminal of the OTA 310 and the input terminal of the comparator 320. This configuration is for initializing the output terminal of the comparator. When the conductance of the OTA is gm, Output current (I _OTA ) and OTA output voltage (V _{OTA_OUT} ) are as follows.

I _OTA = gm (V _IN - V _RLD )

_{V OTA _OUT = (gm (V} IN - V RLD) / C) * t

Figure 6 there is illustrated also is shown illustrating the output of the QTC negative input signal according to one embodiment of the present invention, that is, the output voltage (V _{OTA _OUT)} of the OTA (310) is a reference voltage and the bio-signal (V _IN) (A region) with respect to the difference between the output voltage V _RLD and the reference voltage V _RLD , and the output of the comparator becomes HIGH when the OTA output terminal voltage reaches the comparison voltage V _REFT .

The output of the comparator 320 becomes high (H), which means that a high value output of the pulse type output of the comparator having the low value (low) and the high value (2) is derived. The pulse width PW of this comparator output includes the voltage information of the input (V _IN - V _RLD ) and its formula is as follows.

PW = T - t _rst - C / (gm (V _IN - V _RLD ))

The QTC unit 300 further includes a counter capable of counting a result value output from the comparator 320 for a predetermined period so as to digitize the pulse width so that the input voltage information Can be extracted.

It goes without saying that such a counter can obtain a high-resolution output value by increasing the frequency of a clock.

The QTC unit 300 having the above configuration controls a low pass cutoff frequency by adjusting at least one of the conductance gm of the OTA 310 or the capacitance C of the capacitor connected to the output terminal of the OTA 310. [ Can be adjusted.

This is a feature that can improve one of the above-mentioned problems. By implementing a low-pass cut-off frequency suitable for a bio-signal without using a device having a large resistance value and / or a device having a large capacitance value, Can be integrated in a front-end chip circuit.

Meanwhile, FIG. 7 shows an example of a conventional AD converter stage and an output of a QTC unit according to an embodiment of the present invention.

In the figure, V _OUT is the result of converting the converted digital value back to an analog value (Digital-to-Analog).

In this case, the difference between V _IN and V _OUT is that the conventional AD converter stage converts the sampled voltage during the conversion period to obtain the final result, so that only the input voltage at the sampling time is reflected in the result there is a problem.

However, since the QTC unit 300 of the present invention continuously reflects the input during the conversion period to obtain the final result, it can be confirmed that a more accurate output can be obtained than in the conventional AD converter unit.

Since the difference between the characteristics of the bio-signals continuously generating minute changes is significant in the result of the measurement system, the present invention is characterized in that it can output a clearer result than the conventional bio-signal measurement system.

As a result, the present invention utilizes a QTC unit including an OTA and a comparator in a bio-signal measurement system so that it can be integrated into an analog front-end chip circuit without application of a resistor or a capacitor having such a large value that integration is impossible.

Further, according to the present invention, the A / D converter stage is implemented with a high resolution and the comparison voltage input to the comparator is configured to have a rising section and a falling section instead of a constant level, thereby minimizing a portion missing in the measurement in the bio- There is an advantage that a bio-signal can be measured.

While the present invention has been described with reference to the specific embodiments, it is to be understood that the invention is not limited thereto. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents. Various modifications and variations are possible.

100:
200: High pass filter section
300: QTC department
310: OTA
320: comparator
330: comparison voltage generator

Claims (5)

An amplifying unit for receiving and amplifying a biological signal;
A high pass filter (HPF) unit for passing only a frequency band biomedical signal of a predetermined frequency or higher among the amplified bio-signals; And
A QTC (charge to time converter) unit for signal processing the bio-signal passing through the high-pass filter unit to output a bio-signal measurement result; / RTI >
The QTC unit includes:
An operational transconductance amplifier (OTA) for receiving a bio-signal and a reference voltage passed through the high-pass filter unit and passing an output current reflecting the difference;
A comparator for comparing the output voltage of the OTA with a comparison voltage and outputting a result value; And
A comparison voltage generator for generating a comparison voltage having a rising section and a falling section so as to pass the voltage value within the set range for one period, and inputting the comparison voltage to the comparator; Wherein the bio-signal measuring system comprises:
The method according to claim 1,
Wherein the QTC unit is capable of adjusting a low pass cutoff frequency by adjusting at least one of a conductance (gm) of the OTA or a capacitance (C) of a capacitor connected to an output terminal of the OTA. system.
The apparatus of claim 1, wherein the QTC unit comprises:
Further comprising a counter capable of counting a result value output from the comparator during a predetermined period of time.
The method according to claim 1,
Wherein the amplification unit uses an instrument amplifier.
The method according to claim 1,
Wherein the high-pass filter unit uses one or more of a Bessel filter, a Butterworth filter, or a Chebyshev filter.

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