KR20230105381A - Apparatus for measurementing optical-based bio-signal - Google Patents

Abstract

An optical-based bio-signal measuring device according to an embodiment includes a light-receiving unit including a light-receiving element for receiving an optical signal including light reflected by a living body, and measuring a current converted from an optical signal received by the light-receiving unit. It includes a signal processing unit of an optical-to-digital conversion structure that outputs a digital signal, and an error removing unit that removes an error that may occur due to the influence of the junction capacitance of the light receiving element during operation of the signal processing unit.

Description

Optical-based bio-signal measuring device {APPARATUS FOR MEASUREMENTING OPTICAL-BASED BIO-SIGNAL}

The present invention relates to an apparatus for measuring an optical-based bio-signal.

Types of optical-based bio-signals include photoplethysmography (PPG), which measures changes in blood flow in blood vessels for each heartbeat cycle, and near infrared spectroscopy (NIRS), which indirectly measures brain nerve activity.

Devices for measuring such optical-based bio-signals convert the light reflected from the skin into current through a photodiode or SiPM (silicon photomultiplier), etc. It is obtained by measuring through a signal processing circuit of a (light-to-digital converter, LDC) structure.

However, light-receiving elements such as photodiodes and SiPMs have junction capacitance due to their physical characteristics, which is a problem that reduces accuracy when measuring the light-converted current using an LDC-structured signal processing circuit. there is.

Japanese Patent Laid-Open No. 1994-101815, published on December 12, 1994.

According to an embodiment, an optical-based bio-signal measurement apparatus and method for removing an error that may be caused by a junction capacitance of a light-receiving device during signal processing through optical-to-digital conversion during optical-based bio-signal measurement is provided.

The problem to be solved by the present invention is not limited to those mentioned above, and another problem to be solved that is not mentioned will be clearly understood by those skilled in the art from the description below.

An optical-based bio-signal measuring device according to one aspect includes a light-receiving unit including a light-receiving element for receiving an optical signal including light reflected by a living body, and a current obtained by converting the light signal received by the light-receiving unit to be digitally measured. It includes a signal processing unit of an optical-to-digital conversion structure that outputs a signal, and an error removing unit that removes an error that may occur due to the influence of the junction capacitance of the light receiving element during operation of the signal processing unit.

Here, the error removing unit may remove the error by applying a predetermined voltage to a connection terminal between the light receiving unit and the signal processing unit.

The signal processing unit may include an integrator for charging and discharging an integrating capacitor according to an input current applied according to a switching operation of a switching element connected to the connection terminal, and the error eliminator may include the switching element discharging the integrating capacitor. The connection terminal may be fixed to the predetermined voltage immediately before performing the switching operation.

In the integrator, one input terminal may be connected to the connection terminal through the switching element, a common voltage Vcm may be applied to another input terminal, and the predetermined voltage may be the common voltage Vcm.

The error removing unit is located between an analog buffer receiving a common voltage (Vcm) and an output terminal of the analog buffer and the connection terminal, and controls the application of the output of the analog buffer to the connection terminal according to a switching state. can include

According to an embodiment, the measurement accuracy of the optical-based bio-signal is improved by removing an error that may be affected by the junction capacitance of the light-receiving element during signal processing through optical-to-digital conversion when measuring the optical-based bio-signal. It works.

1 is a circuit diagram showing the configuration of an optical-based bio-signal measuring device according to an embodiment of the present invention.
FIG. 2 is a signal waveform diagram illustrating the operation of the optical-based bio-signal measuring device of FIG. 1 .
FIG. 3 is a simplified circuit diagram of the optical-based biosignal measuring device shown in FIG. 1 .
FIG. 4 is a signal waveform diagram illustrating the operation of the optical-based bio-signal measuring device shown in FIG. 3 except for the error removal unit.
FIG. 5 is a signal waveform diagram illustrating an operation including an error removing unit among the components of the optical-based bio-signal measuring device shown in FIG. 3 .

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the embodiments described below in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, and only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to completely inform the person who has the scope of the invention, and the present invention is only defined by the scope of the claims.

The terms used in this specification will be briefly described, and the present invention will be described in detail.

The terms used in the present invention have been selected from general terms that are currently widely used as much as possible while considering the functions in the present invention, but these may vary depending on the intention of a person skilled in the art or precedent, the emergence of new technologies, and the like. In addition, in a specific case, there is also a term arbitrarily selected by the applicant, and in this case, the meaning will be described in detail in the description of the invention. Therefore, the term used in the present invention should be defined based on the meaning of the term and the overall content of the present invention, not simply the name of the term.

When it is said that a certain part 'includes' a certain element in the entire specification, it means that other elements may be further included without excluding other elements unless otherwise stated.

In addition, the term 'unit' used in the specification means software or a hardware component such as FPGA or ASIC, and 'unit' performs certain roles. However, 'part' is not limited to software or hardware. A 'unit' may be configured to reside in an addressable storage medium and may be configured to reproduce one or more processors. Thus, as an example, 'unit' refers to components such as software components, object-oriented software components, class components and task components, processes, functions, properties, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays and variables. The functionality provided within the components and 'parts' may be combined into a smaller number of elements and 'parts' or further separated into additional elements and 'parts'.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted.

An optical-based bio-signal measuring device according to an embodiment of the present invention converts light reflected from the skin into current through a light-receiving element such as a photodiode or SiPM when light is irradiated on the skin, and converts the light into a signal of a light-to-digital conversion structure measured through processing. Hereinafter, an embodiment using a photodiode as a light receiving element will be described, but the present invention is not limited thereto. The present invention can be applied to all light-receiving elements having junction capacitance, such as photodiodes or SiPMs, and signal processing of light-to-digital conversion structures.

1 is a circuit diagram showing the configuration of an optical-based bio-signal measuring device according to an embodiment of the present invention.

Referring to FIG. 1 , an optical-based bio-signal measuring device 100 according to an embodiment includes a light receiving unit 110, a signal processing unit 120, and an error removing unit 130.

The light receiving unit 110 receives an optical signal including light reflected by a living body. For example, the light receiving unit 110 may include a photodiode, and the photodiode may receive light reflected by a living body and convert it into current. The light receiving unit 110 receives and converts the irradiated light not only by light reflected by the living body but also by ambient light and converts it into current, which causes an error in optical-based biosignal measurement. Therefore, it is necessary to perform processing to remove the influence of ambient light, which will be described again below.

The signal processing unit 120 measures a current converted from an optical signal received by the light receiving unit 110 and outputs the current as a digital signal through optical-to-digital conversion. The signal processing unit 120 may be implemented in various forms if the current converted by the light receiving unit 110 is measured through signal processing of an optical-to-digital conversion structure. According to an embodiment, the signal processing unit 120 includes an integrator 121, a comparator 122, a counter 123, a digital comparator 124, an up/down counter 125, a plurality of current sources (I _{DC, CAN} , I _CH ), and a plurality of switching elements that perform a switching operation by respective switching signals (φ _{DC, CAN} , φ _CH , and φ _IN ).

The error removing unit 130 removes an error that may occur due to the influence of the junction capacitance of the light receiving element during the operation of the signal processing unit 120 . For example, the error removing unit 130 may apply a predetermined voltage to a connection terminal between the light receiving unit 110 and the signal processing unit 120 to remove an error that may occur due to the junction capacitance of the light receiving element.

For example, the signal processing unit 120 charges and discharges the integral capacitor (C _INT ) according to the input current applied according to the switching operation by the switching signal (φ _IN ) of the switching element connected between the light receiving unit 110 and the connection terminal. It may include an integrator 121 that does, and the error removal unit 130 may fix the connection terminal to a predetermined voltage just before the switching signal φ _IN discharges the integrating capacitor C _INT before performing a switching operation. . For example, one input terminal of the integrator 121 may be connected to a connection terminal through a switching element operating on a switching signal φ _IN , and a common voltage Vcm may be applied to the other input terminal, and the error removing unit 130 ) may fix the connection end to the common voltage Vcm immediately before the switching signal φ _IN discharges the integrating capacitor C _INT . The error removing unit 130 is located between the analog buffer BUFF receiving the common voltage Vcm, the connection terminal and the output terminal of the analog buffer BUFF, and _the analog buffer ( BUFF) may include a switching element for regulating the application of the output to the connection terminal.

FIG. 2 is a signal waveform diagram illustrating the operation of the optical-based bio-signal measuring device 100 in FIG. 1 . When a plurality of signal waveforms as illustrated in FIG. 2 are input to the optical-based bio-signal measuring device 100 of FIG. 1, the integrator 121 of the optical-based bio-signal measuring device 100 outputs as shown in FIG. (V _OUT ), and the counter 123 and up/down counter 125 indicate outputs D _DC and D _COUNT as shown in FIG. 2 .

Referring to FIGS. 1 and 2 , the signal waveform applied to the optical-based bio-signal measuring device 100 and the corresponding operation of the optical-based bio-signal measuring device 100 will be described as follows.

신호: 리세트(reset) 신호로서, 광-디지털 변환의 시작을 나타냄과 동시에 전체 회로 블록을 리스트 시킨다.-

Signal: As a reset signal, it indicates the start of optical-to-digital conversion and lists all circuit blocks at the same time.

- EN_BUFF signal: As a buffer enable signal, power consumption is minimized by operating the analog buffer of the error eliminator 130 only when it is high and not operating in other cases. The time when EN_BUFF=high has a very short time (eg, 1/10 or less) compared to the sampling period (T _S ).

신호: 수광부(110)의 포토다이오드에 걸리는 전압으로서, 수광부(110)와 신호처리부(120) 간의 접속단에 동일한 크기의 전압이 걸릴 수 있다. 포토다이오드의 정션 캐패시턴스의 영향으로

가

다 낮아질 수 있고, 이 경우에 신호처리부(120)에 의한 전류 측정 오차가 발생할 수 있다.-

Signal: This is a voltage applied to the photodiode of the light receiving unit 110, and a voltage of the same magnitude may be applied to a connection terminal between the light receiving unit 110 and the signal processing unit 120. Due to the effect of the junction capacitance of the photodiode

go

In this case, an error in current measurement by the signal processing unit 120 may occur.

신호: 스위칭 동작에 따라 오차 제거부(130)를 인에이블 시킴으로써

과

을 동일하게 하여 포토다이오드의 정션 캐패시턴스의 영향으로 발생할 수 있는 전류 측정 오차를 제거할 수 있다.-

Signal: By enabling the error removing unit 130 according to the switching operation

class

By doing the same, it is possible to remove the current measurement error that may occur due to the influence of the junction capacitance of the photodiode.

신호: 생체에 의해 반사되어 수광부(110)에 의해 수광된 광에 의해 변환된 전류에는 LED에 의해 생체에 조사된 광에 의한 전류 성분(

)과 주변의 다른 광들에 의한 전류 성분(

)이 모두 포함될 수 있다. 스위칭 상태에 따라 주변 광들에 의한 전류 성분(

)만이 신호처리부(120)에 제공되게 하거나 LED에 의한 영향이 포함된 전류 성분(

)까지 신호처리부(120)에 제공되게 한다.-

Signal: In the current converted by the light reflected by the living body and received by the light receiving unit 110, the current component due to the light irradiated to the living body by the LED (

) and current components caused by other lights around (

) may be included. Depending on the switching state, the current component by the ambient light (

) is provided to the signal processing unit 120 or the current component including the effect of the LED (

) to be provided to the signal processing unit 120.

- LED signal: by operating the LED for irradiating light to the living body, the photodiode of the light receiving unit 110 receives the light reflected by the living body, and the integrator 121 discharges the integrating capacitor (C _INT ) do.

신호: 생체에 광을 조사하기 위한 LED가 켜져 있는 동안에 수광부(110)의 포토다이오드에는 높은 전류가 흐르는데, 전류원(

)을 동작 시킴으로써 포토다이오드에 흐르는 대부분의 전류를 입력단에서 빼 주어 신호처리부(120)에 의한 신호처리의 높은 정확도를 확보한다.-

Signal: While the LED for irradiating light to the living body is turned on, a high current flows through the photodiode of the light receiving unit 110, and the current source (

) is operated, most of the current flowing in the photodiode is subtracted from the input terminal to ensure high accuracy of signal processing by the signal processing unit 120.

신호: 적분 캐패시터(

)의 연결을 반대로 스위칭 시킴으로써, 주변 광 영향을 제거하는 처리를 수행할 수 있도록 한다.-

Signal: Integral capacitor (

), it is possible to perform processing to remove the influence of ambient light.

신호: 전류원(

)을 동작시킴으로써, 적분 캐패시터(

)의 충전 동작을 수행하며, 비교기(122)와 카운터(123)를 이용해 충전이 끝나면 디지털 값을 얻을 수 있도록 한다.-

Signal: current source (

) by operating the integrating capacitor (

), and the comparator 122 and the counter 123 are used to obtain a digital value when charging is finished.

신호: 광-디지털 변환에 의해 변환된 디지털 값이다.-

Signal: A digital value converted by optical-to-digital conversion.

)를 방전시키는 스위칭 동작을 하기 직전에 수광부(110)의 포토다이오드에 걸리는 전압을

으로 고정시키는 사전 충전(pre-charging) 동작을 수행할 수 있다.When the plurality of signal waveforms as described above are applied to the optical-based bio-signal measuring device 100, the error removing unit 130 converts the switching signal φ _IN to an integrating capacitor (

), the voltage applied to the photodiode of the light receiving unit 110 immediately before the switching operation to discharge

It is possible to perform a pre-charging operation that fixes to .

)를 충전 또는 방전하는 동작을 수행한다.The integrator 121 is an integrating capacitor (according to the current of the input terminal)

) to charge or discharge.

을

과 비교한 값을 출력한다.The comparator 122 is the output voltage of the integrator 121

second

outputs the value compared to

을 출력한다.The counter 123 is a value obtained by counting the operation of the comparator 122

outputs

을

와 비교하며,

를 벗어나는 카운터(123)의 출력

에 대하여 업/다운(up/down) 신호를 발생시킨다.The digital comparator 124 is the output of the counter 123

second

compare with

output of counter 123 outside

Generates an up/down signal for

를 증가시키거나 감소시켜 출력한다.According to the result of counting the output of the digital comparator 124, the up/down counter 125

Increase or decrease the output.

FIG. 3 is a simplified circuit diagram of the optical-based bio-signal measuring device 100 shown in FIG. 1, and FIG. 4 is an operation of the optical-based bio-signal measuring device 100 shown in FIG. 3 except for the error removing unit 130. FIG. 4 is a signal waveform diagram showing an operation including the error removing unit 130 among the components of the optical-based bio-signal measuring device 100 shown in FIG. 3 .

Comparing the operation of the optical-based bio-signal measuring device 100 according to the signal waveform of FIG. 4 with the operation of the optical-based bio-signal measuring device 100 according to the signal waveform of FIG. It can be seen that during the operation of the processing unit 120, an error that may occur due to the influence of the junction capacitance of the photodiode in the light receiving unit 110 is removed. In the description below, we will not consider ambient light effects.

)와 정션 캐패시턴스(

)에 저장된 전하는 다음과 같다.In the signal waveform of FIG. 4, the integrating capacitor just before the discharging phase (

) and junction capacitance (

), the charge stored in

신호에 의해 해당 스위칭 소자가 연결되며, 이때 적분기(121)의 출력

은 아래 식의 둘째 항(second term)과 같은 오차(Verror)를 가진다.Immediately after the discharge phase begins,

The corresponding switching element is connected by the signal, and at this time, the output of the integrator 121

has the same error (Verror) as the second term of the equation below.

보다 낮아져서 발생하는 것이다.This error (Verror) is caused by the discharge of the connection end voltage (Vp) through the photodiode in the waiting phase before the signal processing unit 120 measures the current converted by the light receiving unit 110.

This is what happens when it gets lower.

신호에 의해 해당 스위칭 소자가 연결되기 전에

신호에 의해 오차 제거부(130) 내의 스위칭 소자가 잠깐 동안 연결되며, 이때 수광부(110)와 신호처리부(120) 사이의 접속단의 전압이

으로 고정된다. 따라서,

신호에 의해 해당 스위칭 소자가 연결되는 순간 또한 수광부(110)와 신호처리부(120) 사이의 접속단의 전압은

인 상태이다. 이는 상기한 바와 같은 적분기(121)의 출력

에 대한 수식에서 V_P,waiting = V_CM 으로 만드는 것이기에, 둘째 항(second term)인 오차(Verror)가 사라진다.According to the signal waveform of FIG. 5,

Before the corresponding switching element is connected by the signal

The switching element in the error removing unit 130 is connected for a while by the signal, and at this time, the voltage of the connection terminal between the light receiving unit 110 and the signal processing unit 120 is

is fixed to thus,

The moment the corresponding switching element is connected by the signal, and the voltage of the connection terminal between the light receiving unit 110 and the signal processing unit 120 is

is in a state This is the output of integrator 121 as described above.

Since V _P,waiting = V _CM is made in the formula for , the second term, Verror, disappears.

As described above, according to an embodiment, an error that may be affected by the junction capacitance of a light-receiving element during signal processing through optical-to-digital conversion is removed during optical-based bio-signal measurement, so that the optical-based bio-signal is measured. measurement accuracy is improved.

The above description is merely an example of the technical idea of the present invention, and various modifications and variations can be made to those skilled in the art without departing from the essential qualities of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but to explain, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be construed according to the claims below, and all technical ideas within the scope equivalent thereto should be construed as being included in the scope of the present invention.

100: Optical-based bio-signal measuring device
110: light receiving unit
120: signal processing unit
130: error removal unit

Claims (5)

a light receiving unit including a light receiving element for receiving an optical signal including light reflected by a living body;
a signal processing unit having an optical-to-digital conversion structure for measuring a current converted from an optical signal received by the light receiving unit and outputting the converted current as a digital signal;
And an error removing unit for removing an error that may occur due to the influence of the junction capacitance of the light receiving element during the operation of the signal processing unit.
Optical-based bio-signal measurement device. According to claim 1,
The error removing unit removes the error by applying a predetermined voltage to a connection terminal between the light receiving unit and the signal processing unit.
Optical-based bio-signal measurement device. According to claim 2,
The signal processing unit includes an integrator for charging and discharging an integrating capacitor according to an input current applied according to a switching operation of a switching element connected to the connection terminal,
The error removing unit fixes the connection terminal to the predetermined voltage immediately before the switching element performs a switching operation of discharging the integrating capacitor.
Optical-based bio-signal measurement device. According to claim 3,
In the integrator, one input terminal is connected to the connection terminal through the switching element, and a common voltage (Vcm) is applied to the other input terminal,
The predetermined voltage is a common voltage (Vcm)
Optical-based bio-signal measurement device. According to claim 4,
The error elimination unit,
An analog buffer receiving a common voltage (Vcm);
A switching element positioned between the connection end and the output end of the analog buffer to regulate the application of the output of the analog buffer to the connection end according to a switching state
Optical-based bio-signal measurement device.

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