KR101569499B1 - Amplifying device for detecting EEG signal with improving CMRR - Google Patents

Abstract

An amplifying apparatus for detecting an EEG signal with improved common mode rejection ratio is disclosed. An amplifying apparatus for detecting an EEG signal comprises: a first processing unit for processing an EEG signal input from a first electrode for detecting an EEG signal attached to a human body; A second processing unit for processing an EEG signal input from a second electrode for detecting an EEG signal attached to a human body; And a CMRR improvement loop unit for extracting a common mode signal from the first differential output signal input from the first processing unit and the second differential output signal input from the second processing unit and inputting the common mode signal to the first processing unit and the second processing unit, .

Description

[0001] The present invention relates to an amplifying device for detecting an EEG signal with improved common-

The present invention relates to an amplifying apparatus for detecting an EEG signal with improved common mode rejection ratio.

Electro-encephalogram (EEG) is a waveform obtained by attaching several electrode pads to a person's head and amplifying the electric signals obtained therefrom. The electroencephalogram (EEG) is a waveform that effectively removes noise from a signal measured through an electrode pad, Have been developed variously.

For example, European Patent No. 2294979 (Method and electronic medical device for simultaneous measuring and impedance and a biopotential signal) proposes a device for measuring EEG using a chopper stabilization technique.

The EEG signal detecting apparatus applying the chopper stabilization technique disclosed in the European patent includes an input unit for converting input microvoltages into current signals and outputting them, an output unit for converting the current output from the input unit into a voltage, amplifying and outputting the voltage, And a DC servo loop for removing the DC servo loop. This EEG signal detection device is expected to avoid low frequency noise by applying the chopper stabilization technique.

A high common mode rejection ratio (CMRR) must be obtained at the amplifier in order to obtain high quality biomedical signals.

In order to ensure a high common mode rejection ratio, a technique of setting the reference voltage of the human body using a feedback circuit (Driven Right Leg, DRL) is generally used, which is disclosed in US Pat. No. 5,392,784 (Virtual right leg drive and augmented right leg drive circuits for common mode voltage reduction in ECG and EEG measurements.

The above-described DRL technique is driven to reduce the common mode component of a living body signal generated in the human body by amplifying the common mode signal of the amplifier differential output and performing negative feedback to the human body. Whereby the common mode component measured in the output signal of the amplifier is reduced to show the effect of improving the common mode rejection ratio.

However, when applying the DRL technique described above, since the current is injected into the human body in order to set the reference voltage of the human body, safety problems may be caused. In addition, since the human body acts as a large load on the side of the amplifier, the current consumption is increased and the frequency stability of the amplifier is deteriorated.

It is an object of the present invention to provide an amplifying apparatus for detecting an EEG signal with improved common mode rejection ratio that can be reduced in power and size and can solve the safety problem caused by human body driving.

Other objects of the present invention will become readily apparent from the following description.

For reference, this patent application is developed through the "SW Convergent Parts Technology Development Project", a national research and development project supported by the Ministry of Commerce, Industry and Energy. [10043826, Development of BMI SoC and SW Platform with 2uV Level Noise Countermeasure for Disease Customized Service in Smart Environment]

According to an aspect of the present invention, there is provided an amplifying apparatus for detecting an EEG signal, comprising: a first processing unit for processing an EEG signal input from a first electrode for detecting an EEG signal attached to a human body; A second processing unit for processing an EEG signal input from a second electrode for detecting an EEG signal attached to a human body; And a common processing unit for extracting a common mode signal from a first differential output signal (OUTP) input from the first processing unit and a second differential output signal (OUTN) input from the second processing unit and outputting the common mode signal to the first processing unit Wherein each of the first processing unit and the second processing unit includes a capacitor for removing a noise component from an EEG signal input from a corresponding electrode, and a second common mode rejection ratio An amplifier including an operational amplifier for amplifying and outputting a signal at a predetermined amplification ratio; A low pass filter unit for extracting a low frequency signal of a predetermined frequency band from the output signal of the operational amplifier and feeding back the low frequency signal to a negative input terminal of the operational amplifier; A high pass inversion filter unit for inverting and amplifying an output signal of the operational amplifier to increase an input impedance and feeding back the amplified signal to a negative input terminal of the operational amplifier; And a bandpass filter unit for filtering the signal of a predetermined frequency band among the output signals of the amplifying unit to generate the first or second differential output signal.

And the common mode signal may be inputted to a positive input terminal of the operational amplifier.

The CMRR improvement loop section may include an invertig adder circuit.

The CMRR improvement loop includes an input impedance by a capacitor C _in for summing a first differential output signal OUT _P and a second differential output signal OUT _N so as to ensure a high pass characteristic, _f and a feedback impedance due to the parallel connection of the feedback capacitor C _f .

Each of the first processing unit and the second processing unit may further include a switch unit for shorting an input terminal and an output terminal of the operational amplifier by a control signal.

Other aspects, features, and advantages will become apparent from the following drawings, claims, and detailed description of the invention.

According to the embodiment of the present invention, it is possible to reduce the power consumption and the miniaturization in improving the common mode rejection ratio, and it is possible to solve the safety problem due to the human body driving.

1 is a schematic block diagram of an amplifying apparatus for detecting an EEG signal according to an embodiment of the present invention.
FIG. 2 is a circuit diagram of the amplifying apparatus for detecting an EEG signal shown in FIG. 1. FIG.
3 is a graph simulating the CMRR change state depending on whether the CMRR improvement loop unit operates according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The terms first, second, etc. may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

FIG. 1 is a schematic block diagram of an amplifying apparatus for detecting an EEG signal according to an embodiment of the present invention, FIG. 2 is a circuit diagram of an amplifying apparatus for detecting an EEG signal shown in FIG. 1, 5 is a graph simulating the CMRR change state depending on whether the CMRR improvement loop unit according to the embodiment operates.

1 and 2, the amplifying apparatus for EEG signal detection includes a first amplifying unit 110a, a first switch unit 120a, a first low-pass filter unit 130a, a first high-pass reversal filter unit A first band-pass filter unit 150a, a CMRR improvement loop unit 160, a second amplifier unit 110ba, a second switch unit 120b, a second low-pass filter unit 130b, Pass reverse filter section 140b and a second band-pass filter section 150b.

Here, the first amplification part 110a, the first switch part 120a, the first low-pass filter part 130a, the first high-pass reversal filter part 140a, and the first band-pass filter part 150a, A second switch unit 120b, a second low-pass filter unit 130b, a second low-pass filter unit 130b, and a second low-pass filter unit 130b. The high-pass inversion filter unit 140b and the second band-pass filter unit 150b are connected to a circuit for processing an EEG signal input from a negative electrode for EEG signal detection attached to a human body.

The EEG signals inputted through the EEG signal input terminals IN _P and IN _N are respectively inputted to the first and second amplifying units 110a and 110b connected to the first and second amplifying units 110a and 110b by the input capacitors C _in , And only the AC component is input to the input terminal of the operational amplifier included in the first and second amplifying units 110a and 110b.

The operational amplifier is described in the related paper "A Micro-Power EEG Acquisition SoC Integrated Feature Extraction Processor for a Chronic Seizure Detection System" (Naveen Verma, et al., IEEE JOURNAL OF SOLID STATE CIRCUITS, vol. 45, 2010, which is incorporated herein by reference in its entirety.

The EEG signal input to the operational amplifier is amplified by the feedback capacitor (C _f ) and the feedback resistor (R _f ). Assuming that the feedback resistor R _f is very large, the input and output gains of the first and second amplifying units 110a and 110b can be approximated to C _in / C _f .

It is known that the bandwidth of the EEG signal is generally distributed in the range of 0.5 to 100 Hz and the high-pass filter characteristic of 0.5 Hz is obtained by dividing the feedback capacitor C _f of the first and second amplifying units 110a and 110b and the feedback resistor R _f ). ≪ / RTI >

Since the high-pass filter of the first and second amplifying units 110a and 110b has a very low high-pass cut-off frequency (for example, about 0.5 Hz) To be stabilized up to the first and second switch parts 120a and 120b, respectively.

The first and second switch units 120a and 120b are controlled by a signal of S _Fast . When the switch is turned on (short-circuited), the operational amplifier operates as a buffer and can be quickly stabilized to a desired operating point.

There may be a low frequency signal to be removed in the EEG signal inputted through the EEG signal input terminal and there may be an offset generated in the operational amplifier provided in the first and second amplification units 110a and 110b. First and second low-pass filter units 130a and 130b, which are DC servo loop circuits, are connected in parallel to the first and second amplifying units 110a and 110b to remove such low-frequency signals and offsets.

First and second low pass filter (130a, 130b), by default, the first servo resistance (R _{servo _ in)} and a structure in which buffering a low-pass filter is implemented by a capacitor (C _{servo _ in),} a buffering operation The output voltage of the amplifier is converted into a current through a second servo resistor (R _servo ) and fed back to the input terminals of the operational amplifiers of the first and second amplifying units 110a and 110b.

As shown in FIG. 1 and FIG. 2, the amplifying apparatus for detecting an EEG signal uses the first and second low-pass filter units 130a and 130b to amplify the output of the first and second amplifying units 110a and 110b And a negative feedback structure for extracting the generated low frequency signals and inputting the extracted low frequency signals to the negative input terminals of the operational amplifiers included in the first and second amplifying units 110a and 110b. That is, the first and second low-pass filter sections 130a and 130b are connected to the input terminal of the operational amplifier through negative feedback. The first and second low pass filter sections 130a and 130b extract only low frequency signals of the operational amplifier output signal to implement a negative feedback structure as an input stage and remove low frequency signals at the operational amplifier input stage, The low frequency signal is removed. Thus, the first and second low-pass filter sections 130a and 130b operate as a high-pass filter that removes unnecessary low-frequency offsets from the output of the operational amplifier through negative feedback.

First and second high pass inversion filter part (140a, 140b) performs the function of increasing the input impedance of the first filter capacitor (C _{b _ in),} a second filter capacitor (C _{b _f),} filter resistance ( R _{b _f} ) and an operational amplifier, and a third filter capacitor C _b .

That is, the first and second high-pass inversion filter units 140a and 140b invert and amplify the output signals of the first and second amplification units 110a and 110b and output the amplified signals to the first and second amplification units 110a and 110b It is possible to increase the input impedance by forming a positive feedback loop by feeding back the negative input of the operational amplifier provided.

In this regard, reference can be made to the prior art "A 160 uW 8-Channel Active Electrode System for EEG Monitoring" (Jiawei Xu, IEEE TRANSACTIONS ON BIOMEDICAL CIRCUITS AND SYSTEMS, Vol. 5, No. 6, DECEMBER 2011).

The differential output signals output from the first and second amplifying units 110a and 110b are then input to the first and second bandpass filter units 150a and 150b and output to the first and second bandpass filter units 150a and 150b, 100 Hz) are filtered to obtain the differential output signals OUT _P and OUT _N of the corresponding frequency band.

The CMRR improvement loop unit 160 performs the CMRR improvement on the differential output signals OUT _P and OUT _N input from the first and second band-pass filter units 150a and 150b to improve the common mode rejection ratio (CMRR) And feeds back the mode signal to the inputs of the first and second amplifying units 110a and 110b.

The CMRR improvement loop unit 160 includes an inverting adder circuit and the differential output signals OUT _P and OUT _N are supplied to a capacitor connected to the inverting input terminal of the amplifier included in the CMRR improvement loop unit 160 C _in , and amplified by the feedback resistor R _f and the feedback capacitance C _f . At this time, assuming that the feedback resistor R _f is very large, the input-to-output gain of the CMRR improvement loop unit 160 can be approximated to C _in / C _f .

The output signal of the CMRR improvement loop portions _{(160) (V REF _ CMFB} ) includes a first band-pass filter section (150a) of the differential output signal (OUT of the differential output signal (OUT _P) and the second band pass filter (150b) _N ) are inverted amplified signals.

Therefore, when the output signal of the CMRR improvement loop unit 160 is fed back to the positive input terminals of the first and second amplifying units 110a and 110b, the common mode of the operational amplifier output is inverted and fed back to the input of the operational amplifier A negative feedback loop for the common mode signal is implemented. Thereby, the common mode of the input signal to the first and second amplifying units 110a and 110b is reduced to improve the common mode rejection ratio.

FIG. 3 shows a graph simulating the CMRR change state depending on whether or not the CMRR improvement loop unit operates.

In this simulation, the electrode impedance was attached to only one of the two input terminals (IN _P and IN _N ) on the assumption that the electrode for acquiring the EEG signal was normally attached to one of the two differential input terminals (IN _P and IN _N ).

As a result, it can be confirmed that the CMRR improvement effect of about 10 to 30 dB is obtained when the pink line to which the CMRR improvement loop is applied is compared with the blue line to which the CMRR improvement loop is not applied.

As described above, since the amplifier for detecting the EEG signal according to the present embodiment drives only the input terminal of the operational amplifier without directly driving the human body in order to improve the common mode, it is necessary to implement an output terminal for the operational amplifier for driving a large load There is no advantage. Therefore, the amplifying apparatus for EEG signal detection can be more miniaturized, can be driven at low power, and the safety problem due to human body driving can be eliminated.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention as defined in the following claims And changes may be made without departing from the spirit and scope of the invention.

110a: first amplification unit 110b: second amplification unit
120a: first switch unit 120b: second switch unit
130a: first low-pass filter part 130b: second low-pass filter part
140a: a first high pass inversion filter unit
140b: a first high-pass reversal filter section
150a: first band pass filter part 150b: second band pass filter part
160: CMRR improvement loop unit

Claims (5)

An amplifying apparatus for detecting an EEG signal,
A first processor for processing an EEG signal input from a first electrode for detecting an EEG signal attached to a human body;
A second processing unit for processing an EEG signal input from a second electrode for detecting an EEG signal attached to a human body; And
And an inverting adder circuit for extracting a common mode signal from the first differential output signal OUT _P input from the first processing unit and the second differential output signal OUT _N input from the second processing unit, And a common mode rejection ratio (CMRR) improvement loop unit for inputting the CMRR to the first processor and the second processor,
Wherein each of the first processing section and the second processing section includes:
A capacitor for removing a noise component from an EEG signal inputted from a corresponding electrode; and an operational amplifier including an operational amplifier for amplifying an EEG signal outputted from the capacitor with a predetermined amplification ratio and outputting the amplified EEG signal;
A low pass filter unit for extracting a low frequency signal of a predetermined frequency band from the output signal of the operational amplifier and feeding back the low frequency signal to a negative input terminal of the operational amplifier;
A high pass inversion filter unit for inverting and amplifying an output signal of the operational amplifier to increase an input impedance and feeding back the amplified signal to a negative input terminal of the operational amplifier; And
And a band pass filter unit for filtering the signal of the predetermined frequency band among the output signals of the amplifying unit to generate the first or second differential output signal,
The CMRR improvement loop section includes an input impedance by a capacitor C _in for summing the first differential output signal OUT _P and the second differential output signal OUT _N , Further comprising a feedback impedance due to the parallel connection of the feedback capacitor (R _f ) and the feedback capacitor (C _f ).
The method according to claim 1,
Wherein the common mode signal is input to a positive input terminal of the operational amplifier.
delete delete The method according to claim 1,
Wherein each of the first processing unit and the second processing unit further comprises a switch unit for shorting an input terminal and an output terminal of the operational amplifier by a control signal.

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