CN102258366B - Orthogonal-square-wave-modulation photoelectric volume pulse wave measuring device and measuring method thereof - Google Patents

Abstract

The invention discloses an orthogonal square wave modulation photoplethysmography measuring device and measuring method. A microprocessor outputs orthogonal square waves of different frequencies. The orthogonal square wave drives at least two kinds of light-emitting diodes. The light emitted by the light-emitting diodes passes through The finger under test is received by the photosensitive device, and the photosensitive device converts it into a voltage signal. The processor processes the digital signal, obtains the photoplethysmography wave and its valley and peak value, and obtains the spectrum value through the valley value and peak value. The measurement method includes: the microprocessor separates and processes the digital signal to obtain the photoplethysmography wave and eliminates the interference of background light; obtains the valley value and peak value according to the photoplethysmography wave; calculates the valley value and peak value to obtain the absorbance difference, and uses the absorbance Difference to get spectral values. The invention has the characteristics of accurate measurement and simple circuit.

Description

A kind of orthogonal square wave modulation photoplethysmography measuring device and measuring method

technical field

The invention relates to an orthogonal square wave modulation photoplethysmography measuring device and measuring method.

Background technique

Photo Plethysmo Graphy (PPG) is an important physiological signal widely used in the analysis of cardiovascular system and blood components. For example, the measurement of blood oxygen saturation is achieved by using two or more LEDs (light-emitting diodes) to measure PPG. In these measurements, the time-division method is usually used to collect PPG and eliminate the interference of background light.

The inventor finds in the process of realizing the present invention that there are at least the following disadvantages and deficiencies in the prior art:

The existing multi-wavelength PPG measurement methods have disadvantages such as complex circuit structure, high requirements for devices and processes, difficult debugging, low reliability, large amount of calculation, and inaccurate results.

Contents of the invention

The technical problem to be solved by the present invention is to provide an orthogonal square wave modulation photoplethysmography measurement device and measurement method, which can realize high-precision measurement, and the circuit structure is simple, the device and process requirements are low, and the debugging Easy, high reliability, small amount of calculation and other advantages, see the following description for details:

The invention provides a photoplethysmography measuring device with orthogonal square wave modulation. The photoplethysmography measuring device includes: a microprocessor, at least two kinds of light emitting diodes, a photosensitive device, a current/voltage conversion amplifier and an analog-to-digital conversion device,

The microprocessor outputs orthogonal square waves of different frequencies, and the orthogonal square waves drive at least two kinds of light-emitting diodes, and the light emitted by the light-emitting diodes is received by the photosensitive device after passing through the finger under test. The photosensitive device is converted into a voltage signal, and the voltage signal is converted into a preset amplitude voltage signal by the current/voltage conversion amplifier, and the analog-to-digital converter converts the preset amplitude voltage signal into a digital signal, and the The microprocessor processes the digital signal, obtains the photoplethysmography wave and its valley value and peak value, and obtains the spectral value through the valley value and the peak value.

The microprocessor adopts any one of MCU, ARM, DSP or FPGA.

The present invention provides a kind of orthogonal square wave modulation photoplethysmography measuring method, described method comprises the following steps:

(1) The microprocessor uses orthogonal square waves of different frequencies to drive at least two kinds of light-emitting diodes;

(2) The light emitted by the light-emitting diode is received and converted into a voltage signal by the photosensitive device after passing through the finger under test, and the voltage signal is amplified into a voltage signal of a preset amplitude through a current/voltage conversion amplifier;

(3) The preset amplitude voltage signal is converted into a digital signal by an analog-to-digital converter and sent to the microprocessor;

(4) The microprocessor separates and processes the digital signal to obtain a photoplethysmogram and eliminates the interference of background light;

(5) Obtain valley and peak values according to the photoplethysmogram;

(6) Calculate the valley value and the peak value to obtain an absorbance difference, and obtain a spectral value through the absorbance difference.

A kind of orthogonal square wave modulation photoplethysmography measuring device and measuring method provided by the present invention have the following advantages compared with the prior art:

According to Lambert-Beer's law, the present invention adopts orthogonal square wave frequency division modulation and digital demodulation technology to design a photoplethysmogram and its valley value and peak value of multi-wavelength light-emitting diodes modulated by orthogonal square wave, through the valley value and peak value The device and measurement method for obtaining spectral values have the characteristics of accurate measurement, simple circuit, no debugging, good manufacturability and low cost.

Description of drawings

Fig. 1 is the schematic diagram of the principle of calculating absorbance provided by the present invention;

Fig. 2 is the structural representation of a kind of orthogonal square wave modulation photoplethysmography measuring device provided by the present invention;

Fig. 3 is a schematic diagram of separating photoplethysmography waves of different wavelengths provided by the present invention;

Fig. 4 is the flowchart of a kind of orthogonal square wave modulation photoplethysmography method provided by the present invention;

Fig. 5 is another structural schematic diagram of an orthogonal square wave modulation photoplethysmography measuring device provided by the present invention.

The list of parts represented by each label in the accompanying drawings is as follows:

1: Microprocessor; 2: LED;

3: Photosensitive device; 4: Current/voltage conversion amplifier;

5: Analog-to-digital converter; PX.1: I/O port;

PX.2: I/O port; PX.n: I/O port;

PX.3: I/O port; PX.4: I/O port

R1: the first resistor; VCC: power supply;

R2: the second resistor; R3: the third resistor;

R4: the fourth resistor; R5: the fifth resistor;

R6: the sixth resistor; C1: the first capacitor;

C2: second capacitor; D1: first light-emitting diode;

D2: the second light-emitting diode; D3: the third light-emitting diode;

D4: fourth light-emitting diode; A1: operational amplifier;

PY port: I/O.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the implementation manner of the present invention will be further described in detail below in conjunction with the accompanying drawings.

Due to the pulsation phenomenon of the artery, the blood flow in the blood vessel changes periodically, and the blood is a highly opaque liquid, so the change of the pulsation will inevitably cause the change of the absorbance, as shown in Figure 1.

Considering the state of the lowest arterial vessel filling degree, the incident light from the light source is not absorbed by the pulsating arterial blood, and the outgoing light intensity I _max is the strongest at this time, which can be regarded as the incident light I of the pulsating arterial blood; while the state of the highest arterial vessel filling degree corresponds to The valley point of the photoelectric pulse wave is the moment when the pulsating arterial blood has the greatest effect, and the outgoing light intensity I _min at this time is the weakest, which is the minimum outgoing light intensity I of the pulsating arterial blood. Therefore, by recording the absorbance value when the artery is filled to the maximum and the artery is contracted to the minimum, the influence of all body components with constant absorption characteristics such as skin tissue and subcutaneous tissue on the absorbance can be eliminated.

According to the modified Lambert-Beer law, let I ₀ and I be the incident light intensity and the outgoing light intensity respectively, α is the molecular extinction coefficient, c is the concentration of each component, l is the average optical path length of light in the tissue, and G is given by The light loss caused by scattering, the absorbance A can be expressed as:

$\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; lg</span>}\frac{\mathrm{<span\; class="notranslate">\; I</span>}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2.303</span>}\mathrm{<span\; class="notranslate">\; \&alpha;cl</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

Assuming that the absorption coefficient of biological tissue is μ _a , then μ _a = αc, which can be substituted into formula (1):

A＝-2.303μ _a l+G (2)

In light transmission detection, the absorbance is mainly composed of the absorption and scattering of the transmitted tissue, and blood scattering is relatively small and can be ignored. In this way, G is only contributed by tissue other than pulsating arterial blood, which remains constant during the measurement. Assuming that there are n layers of transmitted tissues except pulsating arterial blood, the absorption coefficient of layer i is μ _ti , the absorption coefficient of arterial blood is μ _ab , the maximum optical path length is l _max when the artery is filled in one photoelectric pulse wave period, and the arterial The minimum optical path length during contraction is l _min , then the absorbance A ₁ when the artery is filled and the absorbance A ₂ when the artery contracts can be expressed as:

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2.303</span>}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; ti</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2.303</span>}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; ab</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

${\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2.303</span>}\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; ti</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2.303</span>}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; ab</span>}}{\mathrm{<span\; class="notranslate">\; l</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; G</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Let l be the difference between l _max and l _min . Since other tissues except pulsating arterial blood are basically stable and do not undergo periodic changes, this part has no effect on absorbance when the artery is filled and contracted, that is, the first component in formula (3) and formula (4) is equal. The difference between the absorbance when the artery is filling and the absorbance when the artery is contracted is:

ΔA=A ₁ −A ₂ =−2.303 μ _ab (l _max −1 _min )=−2.303 μ _ab l (5)

In the above derivation process, the absorption and scattering absorbance components of non-pulsating blood and various layers of tissue have been eliminated, and the absorbance difference ΔA between arterial filling and arterial contraction is only contributed by the pulsating absorption of arterial blood, mainly Reflects changes in the absorption of pulsating arterial blood. In essence, it is equivalent to the influence of other tissues except pulsating arterial blood in the transmitted tissue, skin, muscle and venous blood, leaving only the pure pulsating arterial blood for the measurement of the absorbance difference ΔA . In this way, the effects of individual differences such as skin, bone and muscle are removed.

Assuming that the incident light intensity is I ₀ , and the detection light intensity during arterial filling and arterial contraction is I _min and I _max respectively, then the difference ΔA between the absorbance during arterial filling and the absorbance during arterial contraction is:

$\mathrm{<span\; class="notranslate">\; \&Delta;A</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; A</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; lg</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; lg</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; lg</span>}<span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; max</span>}}}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; min</span>}}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

The absorbance difference ΔA corresponding to the photoplethysmogram can be obtained by measuring the valley value I _min and peak value I _max of each photoplethysmography wave, and the spectral value composed of ΔA _λ1 , ΔA _λ2 ... ΔA _λn can be obtained.

A kind of orthogonal square wave modulation photoplethysmography measuring device, referring to Fig. 2, this photoplethysmography measuring device comprises: microprocessor 1, at least 2 kinds of light-emitting diodes 2, photosensitive device 3, current/voltage conversion amplifier 4 and Analog-to-Digital Converter 5.

The microprocessor 1 outputs orthogonal square waves of different frequencies, and the orthogonal square waves drive at least two kinds of light-emitting diodes 2. The light emitted by the light-emitting diodes 2 is received by the photosensitive device 3 after passing through the finger under test, and the photosensitive device 3 is converted into a voltage signal. The voltage signal is converted into a preset amplitude voltage signal by the current/voltage conversion amplifier 4, the analog-to-digital converter 5 converts the preset amplitude voltage signal into a digital signal, and the microprocessor 1 processes the digital signal to obtain the photoplethysmogram and Its trough and peak value, get the spectral value through the trough and peak value.

Wherein, the number of light emitting diodes 2 is greater than or equal to two. During specific implementation, the number of light emitting diodes 2 is set according to the needs in practical applications, which is not limited in the embodiment of the present invention.

Wherein, the preset amplitude value is set according to requirements in practical applications, which is not limited in this embodiment of the present invention during specific implementation.

Wherein, the microprocessor 1 can adopt any one of MCU, ARM, DSP or FPGA.

A kind of orthogonal square wave modulation photoplethysmography measurement method, see Fig. 3 and Fig. 4, this method comprises the following steps:

101: The microprocessor 1 drives at least two kinds of light-emitting diodes 2 with orthogonal square waves of different frequencies;

102: The light emitted by the light-emitting diode 2 passes through the finger under test and is received and converted into a voltage signal by the photosensitive device 3, and the voltage signal is amplified by the current/voltage conversion amplifier 4 into a preset amplitude voltage signal;

103: The preset amplitude voltage signal is converted into a digital signal by the analog-to-digital converter 5 and sent to the microprocessor 1;

104: The microprocessor 1 separates and processes the digital signal to obtain a photoplethysmography wave and eliminates the interference of background light;

105: Acquiring valley and peak values according to photoplethysmography;

For the sake of simple description, the light-emitting diode 2 with four wavelengths is taken as an example for illustration, assuming that the light-emitting diode 2 with wavelengths of λ1 (D1 light-emitting diode) and λ2 (D2 light-emitting diode) drives the frequency of the quadrature square wave to be twice f, and λ3 ( D3 light-emitting diode) and λ4 (D4 light-emitting diode) wavelengths of light-emitting diodes 2 drive quadrature square wave frequencies are 1 times f, and λ1, λ2 wavelengths of light-emitting diodes 2 drive quadrature square wave frequencies are the same but the phase difference is 90° , λ3, λ4 wavelengths of light-emitting diodes 2 drive quadrature square wave frequency is the same but the phase difference of 90 °.

Assume that the sampling frequency of the analog-to-digital converter 5 is f _S , and f _S =2f, and it is guaranteed to sample between the high and low levels of the λ1 driving signal.

可以表示为：digital signal sequence

It can be expressed as:

${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 7</span>}<span\; class="notranslate">\; )</span>$

和分别为波长λ1、λ2、λ3和λ4的光电容积脉搏波，

为背景光和光敏器件3的暗电流、电流/电压转换放大器4的失调电压的总和信号(简称背景信号)。in,

and are photoplethysmography waves of wavelengths λ1, λ2, λ3 and λ4, respectively,

It is the sum signal of the background light, the dark current of the photosensitive device 3, and the offset voltage of the current/voltage conversion amplifier 4 (referred to as the background signal).

Assuming that the sampling frequency f _S is much higher than the changing frequency of the modulated quadrature square wave signal and background light, it can be approximately considered that the amplitudes of each quadrature square wave signal and the background light signal are not the same in one period of the lowest driving signal frequency. Change. Take the first 8 sample values as an example:

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

和分别为波长λ1、λ2、λ3和λ4的光信号和背景信号的幅值。in,

and are the amplitudes of the optical signal and the background signal at wavelengths λ1, λ2, λ3, and λ4, respectively.

In other words, operations are performed in groups of 8 digital signals in sequence:

${\mathrm{D.}}_{8\mathrm{no}+1}+{\mathrm{D.}}_{8\mathrm{no}+2}-{\mathrm{D.}}_{8\mathrm{no}+3}-{\mathrm{D.}}_{8\mathrm{no}+4}+{\mathrm{D.}}_{8\mathrm{no}+5}+{\mathrm{D.}}_{8\mathrm{no}+6}-{\mathrm{D.}}_{8\mathrm{no}+7}-{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}1}$ n=0, 1, 2...(9)

而且完全消除了背景信号

的影响。That is, the photoplethysmography wave with 4 times the wavelength λ1 is obtained

And it completely eliminates the background signal

Impact.

${\mathrm{D.}}_{8\mathrm{no}+1}-{\mathrm{D.}}_{8\mathrm{no}+2}-{\mathrm{D.}}_{8\mathrm{no}+3}+{\mathrm{D.}}_{8\mathrm{no}+4}+{\mathrm{D.}}_{8\mathrm{no}+5}-{\mathrm{D.}}_{8\mathrm{no}+6}-{\mathrm{D.}}_{8\mathrm{no}+7}+{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}2}$ n=0, 1, 2...(10)

而且完全消除了背景信号

的影响。That is, the photoplethysmography wave with 4 times the wavelength λ2 is obtained

and completely eliminates the background signal

Impact.

${\mathrm{D.}}_{8\mathrm{no}+1}+{\mathrm{D.}}_{8\mathrm{no}+2}+{\mathrm{D.}}_{8\mathrm{no}+3}+{\mathrm{D.}}_{8\mathrm{no}+4}-{\mathrm{D.}}_{8\mathrm{no}+5}-{\mathrm{D.}}_{8\mathrm{no}+6}-{\mathrm{D.}}_{8\mathrm{no}+7}-{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}3}$ n=0, 1, 2...(11)

的影响。That is, the photoplethysmography wave with 4 times the wavelength λ3 is obtained And it completely eliminates the background signal

Impact.

${\mathrm{D.}}_{8\mathrm{no}+1}+{\mathrm{D.}}_{8\mathrm{no}+2}-{\mathrm{D.}}_{8\mathrm{no}+3}-{\mathrm{D.}}_{8\mathrm{no}+4}-{\mathrm{D.}}_{8\mathrm{no}+5}-{\mathrm{D.}}_{8\mathrm{no}+6}+{\mathrm{D.}}_{8\mathrm{no}+7}+{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}4}$ n=0, 1, 2...(12)

而且完全消除了背景信号

的影响。That is, the photoplethysmography wave with 4 times the wavelength λ4 is obtained

And it completely eliminates the background signal

Impact.

Calculating the troughs and peaks of the photoplethysmogram at wavelengths λ1, λ2, λ3 and λ4 respectively: I _minλ1 , I _maxλ1 , I _minλ2 , I _maxλ2 , I _minλ3 , I _maxλ3 , I _minλ4 and I _maxλ4 ;

106: Calculate the valley value and peak value to obtain the absorbance difference, and obtain the spectral value through the absorbance difference.

Each absorbance difference ΔA _λ1 , ΔA _{λ2 ,} .

As shown in Fig. 5, a kind of orthogonal square wave modulation photoplethysmography measuring device adopts four kinds of light emitting diodes 2, four I/O ports PX.1, PX.2, PX.3 and PX.4 respectively drives the first light emitting diode D1, the second light emitting diode D2, the third light emitting diode D3 and the fourth light emitting diode D4 through the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4, the first A light-emitting diode D1, a second light-emitting diode D2, a third light-emitting diode D3 and a fourth light-emitting diode D4 transmit light to the finger to be tested and are received by the photosensitive sensor 3, and the signal received by the photosensitive sensor 3 passes through the operational amplifier A1, The current/voltage conversion amplifier 4 composed of the first capacitor C1, the second capacitor C2, the fifth resistor R5 and the sixth resistor R6 is converted into a preset amplitude voltage signal, and then the analog-to-digital converter 5 drives the LED 2 at the highest frequency The preset amplitude voltage signal is converted into a digital signal at twice the speed and sent to the microprocessor 1 through the PY port. The digital signal is first separated into photoplethysmography signals of different wavelengths in the microprocessor 1: 8 digital signals obtained in each order form a group, according to

${\mathrm{D.}}_{8\mathrm{no}+1}+{\mathrm{D.}}_{8\mathrm{no}+2}-{\mathrm{D.}}_{8\mathrm{no}+3}-{\mathrm{D.}}_{8\mathrm{no}+4}+{\mathrm{D.}}_{8\mathrm{no}+5}+{\mathrm{D.}}_{8\mathrm{no}+6}-{\mathrm{D.}}_{8\mathrm{no}+7}-{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}1}$ n=0,1,2...

${\mathrm{D.}}_{8\mathrm{no}+1}-{\mathrm{D.}}_{8\mathrm{no}+2}-{\mathrm{D.}}_{8\mathrm{no}+3}+{\mathrm{D.}}_{8\mathrm{no}+4}+{\mathrm{D.}}_{8\mathrm{no}+5}-{\mathrm{D.}}_{8\mathrm{no}+6}-{\mathrm{D.}}_{8\mathrm{no}+7}+{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}2}$ n=0,1,2...

${\mathrm{D.}}_{8\mathrm{no}+1}+{\mathrm{D.}}_{8\mathrm{no}+2}+{\mathrm{D.}}_{8\mathrm{no}+3}+{\mathrm{D.}}_{8\mathrm{no}+4}-{\mathrm{D.}}_{8\mathrm{no}+5}-{\mathrm{D.}}_{8\mathrm{no}+6}-{\mathrm{D.}}_{8\mathrm{no}+7}-{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}3}$ n=0,1,2...

${\mathrm{D.}}_{8\mathrm{no}+1}+{\mathrm{D.}}_{8\mathrm{no}+2}-{\mathrm{D.}}_{8\mathrm{no}+3}-{\mathrm{D.}}_{8\mathrm{no}+4}-{\mathrm{D.}}_{8\mathrm{no}+5}-{\mathrm{D.}}_{8\mathrm{no}+6}+{\mathrm{D.}}_{8\mathrm{no}+7}+{\mathrm{D.}}_{8\mathrm{no}+8}={4\mathrm{D.}}_{\mathrm{An}}^{\mathrm{\&lambda;}4}$ n=0,1,2...

和

而且完全消除了背景信号

的影响。That is, the photoplethysmography waves with wavelengths λ1, λ2, λ3 and λ4 of 4 times are obtained respectively

and

And it completely eliminates the background signal

Impact.

Obtain the photoplethysmography wave of each wavelength, and calculate the valley and peak value of the photoplethysmography wave of λ1, λ2, λ3 and λ4 accordingly: I _minλ1 , I _maxλ1 , I _minλ2 , I _maxλ2 , I _minλ3 , I _maxλ3 , I _minλ4 and I _maxλ4 .

Then calculate the absorbance difference ΔA corresponding to each wavelength from I _minλ1 , I _maxλ1 , I _minλ2 , I _maxλ2 , I _minλ3 , I _maxλ3 , I _minλ4 and I _maxλ4 , and the absorbance difference ΔA _λ1 , ΔA _λ2 ... ΔA can be obtained Spectral values composed of _λn .

To sum up, the embodiment of the present invention provides an orthogonal square wave modulation photoplethysmography measurement device and measurement method. The embodiment of the present invention adopts the orthogonal square wave frequency division modulation and digital solution based on the Lambert-Beer law. Modulation technology to design an orthogonal square wave modulation photoplethysmogram of multi-wavelength light-emitting diodes and its valley and peak values, and a device and measurement method for obtaining spectral values through valleys and peaks. It has the advantages of accurate measurement, simple circuit, no need for debugging, and process Good performance and low cost.

Those skilled in the art can understand that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the above-mentioned embodiments of the present invention are for description only, and do not represent the advantages and disadvantages of the embodiments.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (1)

1. A measuring method of an orthogonal square wave modulation photoplethysmography measuring device, characterized in that, the method comprises the following steps: (1) The microprocessor uses orthogonal square waves of different frequencies to drive at least two kinds of light-emitting diodes; (2) The light emitted by the light-emitting diode is received and converted into a voltage signal by the photosensitive device after passing through the finger under test, and the voltage signal is amplified into a voltage signal of a preset amplitude through a current/voltage conversion amplifier; (3) The preset amplitude voltage signal is converted into a digital signal by an analog-to-digital converter and sent to the microprocessor; (4) The microprocessor separates and processes the digital signal to obtain a photoplethysmogram and eliminates the interference of background light; (5) Obtain valley and peak values according to the photoplethysmogram; (6) calculating the valley value and the peak value to obtain an absorbance difference, and obtaining a spectral value through the absorbance difference; Wherein, the step of obtaining the valley value and the peak value according to the photoplethysmogram is specifically: λ1 and λ2 wavelength LEDs drive quadrature square wave frequency is 2 times f, λ3 and λ4 wavelength LEDs drive quadrature square wave frequency is 1 times f, λ1, λ2 wavelength LEDs drive quadrature square wave frequency The same but with a phase difference of 90°, the driving quadrature square waves of the light-emitting diodes with wavelengths of λ3 and λ4 have the same frequency but a phase difference of 90°; the sampling frequency of the analog-to-digital converter is f _S , and f _S =2f; digital signal sequence

Expressed as: ${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}$ in,

and

are photoplethysmography waves of wavelengths λ1, λ2, λ3 and λ4, respectively,

It is the sum signal of the background light and the dark current of the photosensitive device and the offset voltage of the current/voltage conversion amplifier; the sampling frequency f _S is much higher than the frequency of the modulation quadrature square wave signal and the change frequency of the background light, and it is one period of the lowest driving signal frequency It is considered that the amplitude of each orthogonal square wave signal and the amplitude of the background light signal remain unchanged: $\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}\\ {\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}\end{array}\right.$ ${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}$ ${\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 4</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 5</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 6</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 7</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; A</span>}}^{\mathrm{<span\; class="notranslate">\; B</span>}}$ in, and

are the amplitudes of optical signals and background signals of wavelengths λ1, λ2, λ3 and λ4, respectively; Perform operations in groups of 8 digital signals in sequence: $\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 7</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; An</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1,2</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>\end{array}$ That is, the photoplethysmography wave with 4 times the wavelength λ1 is obtained

And it completely eliminates the background signal

Impact; $\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 7</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; An</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1,2</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>\end{array}$ That is, the photoplethysmography wave with 4 times the wavelength λ2 is obtained

And it completely eliminates the background signal

Impact; $\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 7</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; An</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1,2</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>\end{array}$ That is, the photoplethysmography wave with 4 times the wavelength λ3 is obtained and completely eliminates the background signal

Impact; $\begin{array}{cc}{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 5</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 6</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 7</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 8</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; D.</span>}}_{\mathrm{<span\; class="notranslate">\; An</span>}}^{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}\mathrm{<span\; class="notranslate">\; 4</span>}}& \mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0,1,2</span>}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span>\end{array}$ That is, the photoplethysmography wave with 4 times the wavelength λ4 is obtained

And it completely eliminates the background signal

Impact; Calculate the troughs and peaks of the photoplethysmogram at wavelengths λ1, λ2, λ3, and λ4, respectively: I _minλ1 , I _maxλ1 , I _minλ2 , I _maxλ2 , I _minλ3 , I _maxλ3 , I _minλ4 , and I _maxλ4 .

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