CN106344040A

CN106344040A - Measuring device and measuring method for raised level square wave modulation photoelectric volume pulse wave

Info

Publication number: CN106344040A
Application number: CN201610915756.8A
Authority: CN
Inventors: 李刚; 刘爱; 王绍辉; 林凌
Original assignee: Tianjin University
Current assignee: Tianjin University
Priority date: 2016-10-20
Filing date: 2016-10-20
Publication date: 2017-01-25

Abstract

The invention discloses a square wave modulation photoplethysmography measuring device and method for raising the level. The microprocessor outputs square waves with different frequencies and a ratio of twice the preset level to drive at least 4 A light-emitting diode; the light emitted by the light-emitting diode is received by the photosensitive device after being tested by the finger, and 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; the digital signal is processed by the microprocessor. Process and obtain the photoplethysmogram and its valley and peak values to obtain the spectral value; in the process of photoelectric signal collection by the photosensitive device, the noise level does not change, but the square wave signal used as the drive increases the preset level. In the low-level part of the wave signal, the square wave signal is significantly improved compared to the noise, thereby improving the signal-to-noise ratio of the photoelectric signal obtained by the photosensitive device in the low-level section of the square wave signal, thereby improving the digital input to the computer. signal precision.

Description

Elevated level square wave modulation photoplethysmography measuring device and measuring method

技术领域technical field

本发明涉及光电容积脉搏波测量领域，本发明涉及一种抬高电平的方波调制光电脉搏容积波测量装置和测量方法。The invention relates to the field of photoplethysmography measurement, and the invention relates to a square wave modulation photoelectric plethysmography measurement device and a measurement method with elevated levels.

背景技术Background technique

光电容积脉搏波(Photo Plethysmo Graphy，以下简称PPG)是一种重要的生理信号，广泛地应用对心血管系统和血液成分进行分析。如对血氧饱和度的测量中就是采用2种或2种以上的LED(发光二极管)测量PPG而实现的。在这些测量中通常采用时分方式采集PPG并消除背景光的干扰。Photoplethysmography (Photo Plethysmo Graphy, hereinafter referred to as 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.

为了提高测量精度，现有技术中的公告号为CN 102389313A，公告日为2012年3月28的专利申请利用方波作为激励信号来提高信号测量的质量。In order to improve the measurement accuracy, the patent application in the prior art with the announcement number of CN 102389313A and the announcement date of March 28, 2012 uses a square wave as an excitation signal to improve the quality of signal measurement.

由于现有的测量装置无一例外地均采用模数转换器，模数转换器在靠近输入极限(最大或最小幅值)时存在显著的非线性，特别是输入模数转换器的模拟信号电平越低，得到的数字转换结果的不确定度越大。Since the existing measurement devices all use analog-to-digital converters without exception, there is significant nonlinearity when the analog-to-digital converter is close to the input limit (maximum or minimum amplitude), especially the analog signal voltage input to the analog-to-digital converter. The lower the level, the greater the uncertainty in the obtained digital conversion result.

因此，采用纯净方波作为激励信号时，在方波的低电平部分得到的数字信号的信噪比就很低，从而影响了信号的测量精度。Therefore, when a pure square wave is used as the excitation signal, the signal-to-noise ratio of the digital signal obtained in the low-level part of the square wave is very low, thereby affecting the measurement accuracy of the signal.

发明内容Contents of the invention

为了改进现有技术中的不足，本发明要解决的技术问题在于提供一种抬高电平的方波调制光电容积脉搏波测量装置和测量方法，该测量装置和测量方法可以实现高精度测量，且电路结构简单、器件和工艺要求低、调试容易、可靠性高、计算量小等优点，详见下文描述：In order to improve the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a square-wave modulated photoplethysmography measurement device and measurement method that raises the level, and the measurement device and measurement method can realize high-precision measurement, And it has the advantages of simple circuit structure, low device and process requirements, easy debugging, high reliability, and small amount of calculation. See the description below for details:

一种抬高电平的方波调制光电容积脉搏波测量装置，所述光电容积脉搏波测量装置包括：微处理器、至少2种发光二极管、光敏器件、电流/电压转换放大器和模数转换器，A square wave modulated photoplethysmography measuring device with elevated levels, said photoplethysmography measuring device comprising: a microprocessor, at least two kinds of light emitting diodes, a photosensitive device, a current/voltage conversion amplifier and an analog-to-digital converter ,

所述微处理器输出不同频率且成2倍比率关系的抬高电平的方波，所述抬高电平的方波驱动所述至少2种发光二极管，所述发光二极管发出的光经被测手指后被所述光敏器件接收，所述光敏器件转换成电压信号，所述电压信号经所述电流/电压转换放大器转换成预设幅值电压信号；The microprocessor outputs square waves with elevated levels at different frequencies and in a 2-fold ratio, and the square waves with elevated levels drive the at least two types of light-emitting diodes, and the light emitted by the light-emitting diodes is After the finger is measured, it is received by the photosensitive device, and 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;

所述模数转换器将所述预设幅值电压信号转换成数字信号，所述微处理器对所述数字信号进行处理，获取光电容积脉搏波及其谷值和峰值，通过所述谷值和所述峰值得到光谱值；The analog-to-digital converter converts the preset amplitude voltage signal into a digital signal, and the microprocessor processes the digital signal to obtain a photoplethysmogram and its valley and peak values, and through the valley and The peak value is obtained as a spectral value;

在光敏器件采集光电信号的过程中，噪声水平没有发生变化，但作为驱动的方波信号由于抬高了预设电平，在方波信号的低电平部分，方波信号相较于噪声改善明显，从而提高了在方波信号低电平段，光敏器件获取到光电信号的信噪比，进而提高了输入到计算机中的数字信号的精度。In the process of collecting the photoelectric signal by the photosensitive device, the noise level does not change, but the square wave signal used as the drive increases the preset level. In the low level part of the square wave signal, the square wave signal is improved compared with the noise. Obviously, thereby improving the signal-to-noise ratio of the photoelectric signal obtained by the photosensitive device in the low-level section of the square wave signal, thereby improving the accuracy of the digital signal input to the computer.

所述作为驱动的方波信号由于抬高了预设电平，在方波信号的高电平部分，提高了光敏器件获取到光电信号的信噪比。The square wave signal used as the drive increases the preset level, and in the high level part of the square wave signal, the signal-to-noise ratio of the photoelectric signal obtained by the photosensitive device is improved.

所述预设电平的取值为光敏器件采集的光电信号动态范围一半以上最佳。The optimal value of the preset level is more than half of the dynamic range of the photoelectric signal collected by the photosensitive device.

所述微处理器采用MCU、ARM、DSP或FPGA中的任意一种。The microprocessor adopts any one of MCU, ARM, DSP or FPGA.

一种抬高电平的方波调制光电容积脉搏波测量装置的测量方法，所述方法包括以下步骤：A method for measuring a level-raised square wave modulated photoplethysmography measuring device, the method comprising the following steps:

(1)微处理器采用不同频率且成2倍比率关系的抬高电平的方波驱动至少2种发光二极管；(1) The microprocessor drives at least two kinds of light-emitting diodes with square waves of different frequencies and raised levels in a 2-fold ratio;

(2)所述发光二极管发出的光经过被测手指后由光敏器件接收转换成电压信号，所述电压信号经过电流/电压转换放大器放大成预设幅值电压信号；(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 preset amplitude voltage signal through a current/voltage conversion amplifier;

(3)所述预设幅值电压信号经模数转换器转换成数字信号送入所述微处理器；(3) The preset amplitude voltage signal is converted into a digital signal by an analog-to-digital converter and sent to the microprocessor;

(4)所述微处理器对所述数字信号进行分离处理得到光电容积脉搏波并消除背景光的干扰；(4) The microprocessor separates and processes the digital signal to obtain a photoplethysmogram and eliminates the interference of background light;

(5)根据所述光电容积脉搏波获取谷值和峰值；(5) Obtain valley and peak values according to the photoplethysmogram;

(6)对所述谷值和所述峰值进行计算得到吸光度差值，通过所述吸光度差值获取光谱值。(6) Calculate the valley value and the peak value to obtain an absorbance difference, and obtain a spectral value through the absorbance difference.

本发明提供的一种抬高电平的方波调制光电容积脉搏波测量装置和测量方法，与现有技术相比具有如下的优点：The invention provides a square-wave modulated photoplethysmography measurement device and measurement method with increased level, which has the following advantages compared with the prior art:

本发明依据朗伯-比尔定律，采用方波频分调制和数字解调技术，相较于背景技术中的公告号为CN 102389313A，公告日为2012年3月28的专利申请，本发明采用抬高预设电平的方波驱动至少2种发光二极管，发光二极管发出的光经被测手指后被光敏器件接收，进而通过电流/电压转换放大器转换成预设幅值电压信号，通过模数转换器将预设幅值电压信号转换成数字信号；微处理器对数字信号进行处理，获取到光谱值。本发明显著地提高了在方波信号低电平段的光电信号的信噪比，改善了预设幅值电压信号，从而提高了信号采集的精度，满足了实际应用中的多种需要。According to the Lambert-Beer law, the present invention adopts square wave frequency division modulation and digital demodulation technology. A square wave with a high preset level drives at least two kinds of light-emitting diodes. The light emitted by the light-emitting diodes is received by the photosensitive device after passing through the finger under test, and then converted into a voltage signal with a preset amplitude by a current/voltage conversion amplifier, and then converted by analog to digital. The converter converts the preset amplitude voltage signal into a digital signal; the microprocessor processes the digital signal to obtain the spectral value. The invention significantly improves the signal-to-noise ratio of the photoelectric signal in the low-level section of the square wave signal, improves the preset amplitude voltage signal, thereby improving the accuracy of signal collection and meeting various needs in practical applications.

附图说明Description of drawings

图1为本发明提供的计算吸光度的原理示意图；Fig. 1 is the schematic diagram of the principle of calculating absorbance provided by the present invention;

图2为本发明提供的一种抬高电平的方波调制光电容积脉搏波测量装置的结构示意图；Fig. 2 is a schematic structural view of a square-wave modulated photoplethysmography measuring device with elevated levels provided by the present invention;

图3为本发明提供的抬高电平的方波的示意图；Fig. 3 is the schematic diagram of the raised level square wave provided by the present invention;

图4为本发明提供的一种抬高电平的方波调制光电容积脉搏波测量方法的流程图；Fig. 4 is a flow chart of a square wave modulated photoplethysmography method for raising the level provided by the present invention;

图5为本发明提供的一种抬高电平的方波调制光电容积脉搏波测量装置的另一结构示意图。Fig. 5 is another structural schematic diagram of a square-wave modulated photoplethysmography measuring device provided by the present invention.

附图中各标号所代表的部件列表如下：The list of parts represented by each label in the accompanying drawings is as follows:

1：微处理器； 2：发光二极管；1: Microprocessor; 2: LED;

3：光敏器件； 4：电流/电压转换放大器；3: Photosensitive device; 4: Current/voltage conversion amplifier;

5：模数转换器； PX.1：I/O口；5: Analog-to-digital converter; PX.1: I/O port;

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

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

R1：第一电阻； VCC：电源；R1: first resistor; VCC: power supply;

R2：第二电阻； R3：第三电阻；R2: second resistor; R3: third resistor;

R4：第四电阻； R5：第五电阻；R4: fourth resistor; R5: fifth resistor;

R6：第六电阻； C1：第一电容；R6: sixth resistor; C1: first capacitor;

C2：第二电容； D1：第一发光二极管；C2: second capacitor; D1: first light emitting diode;

D2：第二发光二极管； D3：第三发光二极管；D2: second light emitting diode; D3: third light emitting diode;

D4：第四发光二极管； A1：运算放大器；D4: fourth light-emitting diode; A1: operational amplifier;

PY口：I/O口。PY port: I/O port.

具体实施方式detailed description

为使本发明的目的、技术方案和优点更加清楚，下面将结合附图对本发明实施方式作进一步地详细描述。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.

实施例1Example 1

由于动脉的脉动现象，使血管中血流量呈周期性变化，而血液是高度不透明液体，因此脉搏搏动的变化必然引起吸光度的变化，如图1所示。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.

考虑动脉血管充盈度最低状态，来自光源的入射光没有被脉动动脉血液吸收，此时的出射光强I_max最强，可视为脉动动脉血液的入射光I；而动脉血管充盈度最高状态对应光电脉搏波的谷点，即脉动动脉血液作用最大的时刻，此时的出射光强I_min最弱，为脉动动脉血液的最小出射光强I。所以，通过记录动脉充盈至最大与动脉收缩至最小时的吸光度值，就可以消除皮肤组织、皮下组织等一切具有恒定吸收特点的人体成分对于吸光度的影响。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.

根据修正的朗伯－比尔定律，设I₀、I分别为入射光强和出射光强，α为分子消光系数，c为各成分浓度，l为光在组织中的平均光路长，G是由散射引起的光损失，则吸光度A可表示为：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:

$A A = = - - l l g g \frac{I I}{{I I}_{00}} = = - - 2.303 2.303 α α c c l l + + G G - - - - - - ((11))$

设生物组织的吸收系数为μ_a，则μ_a＝αc，代入式(1)可得：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_al+G (2)A＝-2.303μ _a l+G (2)

在光透射检测中，吸光度主要由被透射组织的吸收与散射构成，其中血液散射相对较小，可忽略不计。这样，G仅仅由除了脉动动脉血外的组织贡献，在测量过程中保持不变。设除脉动动脉血外的被透射组织共n层，第i层的吸收系数为μ_ti，动脉血的吸收系数为μ_ab，一个光电脉搏波周期上动脉充盈时最大光路长为l_max，动脉收缩时的最小光路长为l_min，则动脉充盈时吸光度A₁和动脉收缩时吸光度A₂可分别表示为：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:

${A A}_{11} = = - - 2.303 2.303 {Σ Σ}_{i i = = 11}^{n no} {μ μ}_{t t i i} {l l}_{m m a a x x} - - 2.303 2.303 {μ μ}_{a a b b} {l l}_{m m a a x x} + + G G - - - - - - ((33))$

${A A}_{22} = = - - 2.303 2.303 {Σ Σ}_{i i = = 11}^{n no} {μ μ}_{t t i i} {l l}_{m m i i n no} - - 2.303 2.303 {μ μ}_{a a b b} {l l}_{m m i i n no} + + G G - - - - - - ((44))$

设l为l_max与l_min之差。由于除了脉动动脉血液以外的其他组织基本稳定，不进行周期变化，因此该部分在动脉充盈和收缩时对吸光度没有影响，即式(3)和式(4)中的第一个分量相等。则动脉充盈时的吸光度和动脉收缩时的吸光度之差为：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＝A₁-A₂＝-2.303μ_ab(l_max-l_min)＝-2.303μ_abl (5)ΔA=A ₁ −A ₂ =−2.303 μ _ab (l _max −1 _min )=−2.303 μ _ab l (5)

在上面的推导过程中，非脉动血液和各层组织的吸收和散射的吸光度分量都被消掉了，动脉充盈时和动脉收缩时的吸光度差值ΔA仅由动脉血的脉动吸收部分贡献，主要反映脉动的动脉血的吸收变化。在本质上相当于在被透射组织中、皮肤、肌肉以及静脉血液等除脉动动脉血液外的其他组织的影响都被去除了，只留下纯粹的脉动动脉血部分来进行吸光度差值ΔA的测量。这样一来，皮肤、骨骼和肌肉等个体差异的影响都被去除了。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.

设入射光强为I₀，动脉充盈时检测光强和动脉收缩时检测光强分别为I_min和I_max，则动脉充盈时的吸光度和动脉收缩时的吸光度差值ΔA为：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:

$M m = = {A A}_{11} - - {A A}_{22} = = l l g g ((\frac{{I I}_{00}}{{I I}_{m m i i n no}})) - - l l g g ((\frac{{I I}_{00}}{{I I}_{m m a a x x}})) = = l l g g ((\frac{{I I}_{m m a a x x}}{{I I}_{m m i i n no}})) - - - - - - ((66))$

测量各个光电容积脉搏波的谷值I_min和峰值I_max即可得到光电容积脉搏波所对应的吸光度差值ΔA，可以得到由ΔA_λ1、ΔA_λ2……ΔA_λn组成的光谱值。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.

一种抬高电平的方波调制光电容积脉搏波测量装置，参见图2，该抬高电平的方波调制光电容积脉搏波测量装置包括：微处理器1、至少2种发光二极管2、光敏器件3、电流/电压转换放大器4和模数转换器5，A square wave modulated photoplethysmography measuring device with raised level, see Fig. 2, the square wave modulated photoplethysmographic measuring device with raised level comprises: a microprocessor 1, at least two kinds of light emitting diodes 2, Photosensitive device 3, current/voltage conversion amplifier 4 and analog-to-digital converter 5,

微处理器1输出不同频率且成2倍比率关系的抬高电平的方波，抬高电平的方波驱动至少2种发光二极管2，发光二极管2发出的光经被测手指后被光敏器件3接收，光敏器件3转换成电压信号，电压信号经电流/电压转换放大器4转换成预设幅值电压信号，模数转换器5将预设幅值电压信号转换成数字信号，微处理器1对数字信号进行处理，获取光电容积脉搏波及其谷值和峰值，通过谷值和峰值得到光谱值。The microprocessor 1 outputs square waves with different frequencies and a ratio of 2 times, and the square waves with high levels drive at least two kinds of light-emitting diodes 2, and the light emitted by the light-emitting diodes 2 is photosensitive after passing through the finger to be tested. Received by the device 3, 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 Process the digital signal, obtain the photoplethysmography wave and its valley and peak, and obtain the spectral value through the valley and peak.

本发明实施例抬高预设电平后，在光敏器件3采集光电信号的过程中，噪声水平没有发生变化，但作为驱动的方波信号由于抬高了预设电平，在方波信号的低电平部分，方波信号相较于噪声改善明显，从而提高了在方波信号低电平段的光电信号的信噪比；相较于背景技术中的公告号为CN 102389313A，公告日为2012年3月28的以纯净方波作为激励信号的专利申请，本发明实施例显著地提高了在方波信号低电平段的光电信号的信噪比，进而改善了光敏器件3获取到光电信号的质量。After the embodiment of the present invention raises the preset level, the noise level does not change during the process of photoelectric signal collection by the photosensitive device 3, but the square wave signal used as the drive is lowered in the square wave signal due to the raised preset level. In the low-level part, the square wave signal is significantly improved compared to the noise, thereby improving the signal-to-noise ratio of the photoelectric signal in the low-level section of the square wave signal; compared with the background technology, the announcement number is CN 102389313A, and the announcement date is On March 28, 2012, a patent application using a pure square wave as the excitation signal, the embodiment of the present invention significantly improves the signal-to-noise ratio of the photoelectric signal in the low-level segment of the square wave signal, thereby improving the photoelectric signal obtained by the photosensitive device 3. The quality of the signal.

另外，由于抬高预设电平，噪声水平没有变化，在方波信号的高电平部分，方波信号相较于噪声也有一定的改善，提高了在方波信号高电平段的光电信号的信噪比。In addition, due to raising the preset level, the noise level does not change. In the high level part of the square wave signal, the square wave signal has a certain improvement compared with the noise, which improves the photoelectric signal in the high level part of the square wave signal. signal-to-noise ratio.

进而，由于光敏器件3获取到的光电信号的信噪比整体增强，进而提高了输入到微处理器1中的数字信号的精度，微处理器1对数字信号进行处理可以得到光谱值。Furthermore, since the overall signal-to-noise ratio of the photoelectric signal acquired by the photosensitive device 3 is enhanced, the precision of the digital signal input to the microprocessor 1 is improved, and the microprocessor 1 processes the digital signal to obtain spectral values.

其中，预设电平的取值优选光敏器件3采集的光电信号动态范围一半以上时，当大于等于1/2动态范围时，通过光敏器件3采集到的光电信号质量最高。Among them, the value of the preset level is preferably when the dynamic range of the photoelectric signal collected by the photosensitive device 3 is more than half, and when it is greater than or equal to 1/2 of the dynamic range, the quality of the photoelectric signal collected by the photosensitive device 3 is the highest.

模数转换器5将预设幅值电压信号转换成数字信号，微处理器1对数字信号进行处理，获取光电容积脉搏波及其谷值和峰值，通过谷值和峰值得到光谱值。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 valley and peak values, and obtain spectral values through the valleys and peaks.

其中，发光二极管2的数量大于等于2。具体实现时，发光二极管2的数量根据实际应用中的需要进行设定，本发明实施例对此不做限制。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.

其中，预设幅值根据实际应用中的需要进行设定，具体实现时，本发明实施例对此不做限制。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.

其中，微处理器1可以采用MCU、ARM、DSP或FPGA中的任意一种。Wherein, the microprocessor 1 can adopt any one of MCU, ARM, DSP or FPGA.

综上所述，由于本发明实施例相对于背景技术中的申请文件，显著地提高了在方波低电平段的光电信号的信噪比，且也提高了在方波信号高电平段的光电信号的信噪比，进而提高了整个电平段的光电信号信噪比，提高了输入到微处理器中的数字信号的精度，微处理器对数字信号进行处理可以得到光谱值。In summary, compared with the application documents in the background technology, the embodiment of the present invention significantly improves the signal-to-noise ratio of the photoelectric signal in the low-level segment of the square wave, and also improves the signal-to-noise ratio in the high-level segment of the square wave signal. The signal-to-noise ratio of the photoelectric signal, which in turn improves the signal-to-noise ratio of the photoelectric signal in the entire level segment, and improves the accuracy of the digital signal input to the microprocessor. The microprocessor can process the digital signal to obtain the spectral value.

实施例2Example 2

一种抬高电平的方波调制光电容积脉搏波测量方法，参见图3和图4，该方法包括以下步骤：A square-wave modulated photoplethysmography method for raising the level, see Fig. 3 and Fig. 4, the method comprises the following steps:

101：微处理器1采用不同频率且成2倍比率关系的抬高电平的方波驱动至少2种发光二极管2；101: The microprocessor 1 drives at least two types of light-emitting diodes 2 with square waves of different frequencies and raised levels in a ratio of 2;

102：发光二极管2发出的光经过被测手指后由光敏器件3接收转换成电压信号，电压信号经过电流/电压转换放大器4放大成预设幅值的电压信号；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 voltage signal with a preset amplitude;

103：电压信号经模数转换器5转换成数字信号送入微处理器1；103: the voltage signal is converted into a digital signal by the analog-to-digital converter 5 and sent to the microprocessor 1;

104：微处理器1对数字信号进行分离处理得到光电容积脉搏波并消除背景光的干扰；104: The microprocessor 1 separates and processes the digital signal to obtain a photoplethysmography wave and eliminates the interference of background light;

105：根据光电容积脉搏波获取谷值和峰值；105: Acquiring valley and peak values according to photoplethysmography;

为简便说明起见，以4种波长发光二极管2为例进行说明，假定λ1、λ2、λ3和λ4波长的发光二极管的驱动抬高方波频率分别为8倍f、4倍f、2倍f、1倍f。假定模数转换器5的采样频率为f_S，且f_S＝2f，并保证在λ1驱动信号高、低电平中间采样。For the sake of simplicity, the light-emitting diode 2 with four wavelengths is taken as an example for illustration, assuming that the driving frequency of the light-emitting diodes with λ1, λ2, λ3 and λ4 wavelengths is 8 times f, 4 times f, 2 times f, and 1 time respectively. f. 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.

数字信号序列可以表示为：digital signal sequence It can be expressed as:

${D D.}_{i i}^{t t} = = {D D.}_{i i}^{λ λ 11} + + {D D.}_{i i}^{λ λ 22} + + {D D.}_{i i}^{λ λ 33} + + {D D.}_{i i}^{λ λ 44} + + {D D.}_{i i}^{B B} - - - - - - ((77))$

其中，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，包括各个波长抬高电平部分的作用)。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, including the effect of raising the level of each wavelength).

假定采样频率f_S远高于调制抬高方波信号和背景光的变化频率，在最低驱动信号频率的一个周期可以近似认为各路方波信号的幅值和背景光信号的幅值不变。以最前16个采样数据为例：Assuming that the sampling frequency f _S is much higher than the changing frequency of the modulated elevated square wave signal and background light, it can be approximately considered that the amplitude of each square wave signal and the amplitude of the background light signal remain unchanged in one period of the lowest driving signal frequency. Take the first 16 sampling data as an example:

$\begin{matrix} \{\begin{matrix} {D D.}_{11}^{λ λ 11} = = {D D.}_{33}^{λ λ 11} = = {D D.}_{55}^{λ λ 11} = = {D D.}_{77}^{λ λ 11} = = {D D.}_{99}^{λ λ 11} = = {D D.}_{1313}^{λ λ 11} = = {D D.}_{1515}^{λ λ 11} = = {D D.}_{A A}^{λ λ 11} \\ {D D.}_{22}^{λ λ 11} = = {D D.}_{44}^{λ λ 11} = = {D D.}_{66}^{λ λ 11} = = {D D.}_{88}^{λ λ 11} = = {D D.}_{1010}^{λ λ 11} = = {D D.}_{1212}^{λ λ 11} = = {D D.}_{1414}^{λ λ 11} = = 00 \\ {D D.}_{11}^{λ λ 22} = = {D D.}_{22}^{λ λ 22} = = {D D.}_{55}^{λ λ 22} = = {D D.}_{66}^{λ λ 22} = = {D D.}_{99}^{λ λ 22} = = {D D.}_{1010}^{λ λ 22} = = {D D.}_{1313}^{λ λ 22} = = {D D.}_{1414}^{λ λ 22} = = {D D.}_{A A}^{λ λ 22} \\ {D D.}_{33}^{λ λ 22} = = {D D.}_{44}^{λ λ 22} = = {D D.}_{77}^{λ λ 22} = = {D D.}_{88}^{λ λ 22} = = {D D.}_{1111}^{λ λ 22} = = {D D.}_{1212}^{λ λ 22} = = {D D.}_{1515}^{λ λ 22} = = {D D.}_{1616}^{λ λ 22} = = 00 \\ {D D.}_{11}^{λ λ 33} = = {D D.}_{22}^{λ λ 33} = = {D D.}_{33}^{λ λ 33} = = {D D.}_{44}^{λ λ 33} = = {D D.}_{99}^{λ λ 33} = = {D D.}_{1010}^{λ λ 33} = = {D D.}_{1111}^{λ λ 33} = = {D D.}_{1212}^{λ λ 33} = = {D D.}_{A A}^{λ λ 33} \\ {D D.}_{55}^{λ λ 33} = = {D D.}_{66}^{λ λ 33} = = {D D.}_{77}^{λ λ 33} = = {D D.}_{88}^{λ λ 33} = = {D D.}_{1313}^{λ λ 33} = = {D D.}_{1414}^{λ λ 33} = = {D D.}_{1515}^{λ λ 33} = = {D D.}_{1616}^{λ λ 33} = = 00 \\ {D D.}_{11}^{λ λ 44} = = {D D.}_{22}^{λ λ 44} = = {D D.}_{33}^{λ λ 44} = = {D D.}_{44}^{λ λ 44} = = {D D.}_{55}^{λ λ 44} = = {D D.}_{66}^{λ λ 44} = = {D D.}_{77}^{λ λ 44} = = {D D.}_{88}^{λ λ 44} = = {D D.}_{A A}^{λ λ 44} \\ {D D.}_{99}^{λ λ 44} = = {D D.}_{1010}^{λ λ 44} = = {D D.}_{1111}^{λ λ 44} = = {D D.}_{1212}^{λ λ 44} = = {D D.}_{1313}^{λ λ 44} = = {D D.}_{1414}^{λ λ 44} = = {D D.}_{1515}^{λ λ 44} = = {D D.}_{1616}^{λ λ 44} = = 00 \\ {D D.}_{11}^{B B} = = {D D.}_{22}^{B B} = = {D D.}_{33}^{B B} = = {D D.}_{44}^{B B} = = {D D.}_{55}^{B B} = = {D D.}_{66}^{B B} = = {D D.}_{77}^{B B} = = {D D.}_{88}^{B B} = = {D D.}_{99}^{B B} = = {D D.}_{1010}^{B B} = = {D D.}_{1111}^{B B} = = {D D.}_{1212}^{B B} = = {D D.}_{1313}^{B B} = = {D D.}_{1414}^{B B} \end{matrix} \\ = = {D D.}_{1515}^{B B} = = {D D.}_{1616}^{B B} = = {D D.}_{A A}^{B B} \end{matrix} - - - - - - ((88))$

其中，和分别为波长λ1、λ2、λ3和λ4的光信号和背景信号(包括各个波长抬高电平部分的作用)的幅值。in, and are the amplitudes of optical signals and background signals (including the effect of each wavelength raising the level) of wavelengths λ1, λ2, λ3, and λ4, respectively.

换言之，以顺序每16个数字信号为一组进行运算：In other words, operations are performed in groups of 16 digital signals in sequence:

$\begin{matrix} {D D.}_{1616 n no + + 11} - - {D D.}_{1616 n no + + 22} + + {D D.}_{1616 n no + + 33} - - {D D.}_{1616 n no + + 44} + + {D D.}_{1616 n no + + 55} - - {D D.}_{1616 n no + + 66} + + {D D.}_{1616 n no + + 77} - - {D D.}_{1616 n no + + 88} + + {D D.}_{1616 n no + + 99} - - {D D.}_{1616 n no + + 1010} + + \\ {D D.}_{1616 n no + + 1111} - - {D D.}_{1616 n no + + 1212} + + {D D.}_{1616 n no + + 1313} - - {D D.}_{1616 n no + + 1414} + + {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 11},, n no = = 00,, 11,, 2...... 2...... \end{matrix} - - - - - - ((99))$

即得到8倍的波长λ1的光电容积脉搏波而且完全消除了背景信号(包括各个波长抬高电平部分的作用)的影响。That is, the photoplethysmography wave with 8 times the wavelength λ1 is obtained Moreover, the background signal is completely eliminated (including the effect of raising the level of each wavelength) Impact.

$\begin{matrix} {D D.}_{1616 n no + + 11} + + {D D.}_{1616 n no + + 22} - - {D D.}_{1616 n no + + 33} - - {D D.}_{1616 n no + + 44} + + {D D.}_{1616 n no + + 55} + + {D D.}_{1616 n no + + 66} - - {D D.}_{1616 n no + + 77} - - {D D.}_{1616 n no + + 88} + + {D D.}_{1616 n no + + 99} + + {D D.}_{1616 n no + + 1010} - - \\ {D D.}_{1616 n no + + 1111} - - {D D.}_{1616 n no + + 1212} + + {D D.}_{1616 n no + + 1313} + + {D D.}_{1616 n no + + 1414} - - {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 22},, n no = = 00,, 11,, 2...... 2...... \end{matrix} - - - - - - ((1010))$

即得到8倍的波长λ2的光电容积脉搏波而且完全消除了背景信号(包括各个波长抬高电平部分的作用)的影响。That is, the photoplethysmography wave with 8 times the wavelength λ2 is obtained Moreover, the background signal is completely eliminated (including the effect of raising the level of each wavelength) Impact.

$\begin{matrix} {D D.}_{1616 n no + + 11} + + {D D.}_{1616 n no + + 22} + + {D D.}_{1616 n no + + 33} + + {D D.}_{1616 n no + + 44} - - {D D.}_{1616 n no + + 55} - - {D D.}_{1616 n no + + 66} - - {D D.}_{1616 n no + + 77} - - {D D.}_{1616 n no + + 88} + + {D D.}_{1616 n no + + 99} + + {D D.}_{1616 n no + + 1010} + + \\ {D D.}_{1616 n no + + 1111} + + {D D.}_{1616 n no + + 1212} - - {D D.}_{1616 n no + + 1313} - - {D D.}_{1616 n no + + 1414} - - {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 33},, n no = = 00,, 11,, 2...... 2...... \end{matrix} - - - - - - ((1111))$

即得到8倍的波长λ3的光电容积脉搏波而且完全消除了背景信号(包括各个波长抬高电平部分的作用)的影响。That is, the photoplethysmography wave with 8 times the wavelength λ3 is obtained Moreover, the background signal is completely eliminated (including the effect of raising the level of each wavelength) Impact.

$\begin{matrix} {D D.}_{1616 n no + + 11} + + {D D.}_{1616 n no + + 22} + + {D D.}_{1616 n no + + 33} + + {D D.}_{1616 n no + + 44} + + {D D.}_{1616 n no + + 55} + + {D D.}_{1616 n no + + 66} + + {D D.}_{1616 n no + + 77} + + {D D.}_{1616 n no + + 88} - - {D D.}_{1616 n no + + 99} - - {D D.}_{1616 n no + + 1010} - - \\ {D D.}_{1616 n no + + 1111} - - {D D.}_{1616 n no + + 1212} - - {D D.}_{1616 n no + + 1313} - - {D D.}_{1616 n no + + 1414} - - {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 44},, n no = = 00,, 11,, 2...... 2...... \end{matrix} - - - - - - ((1212))$

即得到8倍的波长λ4的光电容积脉搏波而且完全消除了背景信号(包括各个波长抬高电平部分的作用)的影响。That is, the photoplethysmography wave with 8 times the wavelength λ4 is obtained Moreover, the background signal is completely eliminated (including the effect of raising the level of each wavelength) Impact.

分别计算波长λ1、λ2、λ3和λ4的光电容积脉搏波的谷值和峰值：I_minλ1、I_maxλ1、I_minλ2、I_maxλ2、I_minλ3、I_maxλ3、I_minλ4和I_maxλ4；Calculating the troughs and peaks of photoplethysmography waves of 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：对谷值和峰值进行计算得到吸光度差值，通过吸光度差值获取光谱值。106: Calculate the valley value and peak value to obtain the absorbance difference, and obtain the spectral value through the absorbance difference.

采用公式(6)计算各个波长的吸光度差值ΔA_λ1、ΔA_λ2、……ΔA_λn，并由吸光度差值构成光谱值。Calculate the absorbance difference values _ΔA _λ1 , ΔA _λ2 , .

实施例3Example 3

如图5所示，一种抬高电平的方波调制光电容积脉搏波测量装置，采用了4种发光二极管2，微处理器1的四个I/O口PX.1、PX.2、PX.3和PX.4分别通过第一电阻R1、第二电阻R2、第三电阻R3和第四电阻R4驱动第一发光二极管D1、第二发光二极管D2、第三发光二极管D3和第四发光二极管D4，第一发光二极管D1、第二发光二极管D2、第三发光二极管D3和第四发光二极管D4发出的光透光被测手指被光敏传感器3所接收，光敏传感器3所接收的信号经过由运算放大器A1、第一电容C1、第二电容C2、第五电阻R5和第六电阻R6所组成的电流/电压转换放大器4转换成预设幅值电压信号，然后模数转换器5以最高驱动发光二极管2频率的二倍速度将预设幅值电压信号转换成数字信号通过PY口送入到微处理器1。数字信号在微处理器1先分离出不同波长光电容积脉搏波：每顺序获取的16个数字信号为一组，按照As shown in Figure 5, a square wave modulated photoplethysmography measuring device with raised level uses four kinds of light emitting diodes 2, four I/O ports PX.1, PX.2, PX.3 and PX.4 respectively drive the first light emitting diode D1, the second light emitting diode D2, the third light emitting diode D3 and the fourth light emitting diode through the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 Diode D4, 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 transmit light to the finger under test and are received by the photosensitive sensor 3, and the signal received by the photosensitive sensor 3 passes through the The current/voltage conversion amplifier 4 composed of the operational amplifier A1, 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 is driven at the highest The double speed of the frequency of the LED 2 converts the preset amplitude voltage signal into a digital signal and sends it to the microprocessor 1 through the PY port. The digital signal is first separated into photoplethysmography waves of different wavelengths in the microprocessor 1: 16 digital signals obtained in sequence form a group, according to

$\begin{matrix} {D D.}_{1616 n no + + 11} - - {D D.}_{1616 n no + + 22} + + {D D.}_{1616 n no + + 33} - - {D D.}_{1616 n no + + 44} + + {D D.}_{1616 n no + + 55} - - {D D.}_{1616 n no + + 66} + + {D D.}_{1616 n no + + 77} - - {D D.}_{1616 n no + + 88} + + {D D.}_{1616 n no + + 99} - - {D D.}_{1616 n no + + 1010} + + \\ {D D.}_{1616 n no + + 1111} - - {D D.}_{1616 n no + + 1212} + + {D D.}_{1616 n no + + 1313} - - {D D.}_{1616 n no + + 1414} + + {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 11},, n no = = 00,, 11,, 2...... 2...... \\ {D D.}_{1616 n no + + 11} + + {D D.}_{1616 n no + + 22} - - {D D.}_{1616 n no + + 33} - - {D D.}_{1616 n no + + 44} + + {D D.}_{1616 n no + + 55} + + {D D.}_{1616 n no + + 66} - - {D D.}_{1616 n no + + 77} - - {D D.}_{1616 n no + + 88} + + {D D.}_{1616 n no + + 99} + + {D D.}_{1616 n no + + 1010} - - \\ {D D.}_{1616 n no + + 1111} - - {D D.}_{1616 n no + + 1212} + + {D D.}_{1616 n no + + 1313} + + {D D.}_{1616 n no + + 1414} - - {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 22},, n no = = 00,, 11,, 2...... 2...... \\ {D D.}_{1616 n no + + 11} + + {D D.}_{1616 n no + + 22} + + {D D.}_{1616 n no + + 33} + + {D D.}_{1616 n no + + 44} - - {D D.}_{1616 n no + + 55} - - {D D.}_{1616 n no + + 66} - - {D D.}_{1616 n no + + 77} - - {D D.}_{1616 n no + + 88} + + {D D.}_{1616 n no + + 99} + + {D D.}_{1616 n no + + 1010} + + \\ {D D.}_{1616 n no + + 1111} + + {D D.}_{1616 n no + + 1212} - - {D D.}_{1616 n no + + 1313} - - {D D.}_{1616 n no + + 1414} - - {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 33},, n no = = 00,, 11,, 2...... 2...... \\ {D D.}_{1616 n no + + 11} + + {D D.}_{1616 n no + + 22} + + {D D.}_{1616 n no + + 33} + + {D D.}_{1616 n no + + 44} + + {D D.}_{1616 n no + + 55} + + {D D.}_{1616 n no + + 66} + + {D D.}_{1616 n no + + 77} + + {D D.}_{1616 n no + + 88} - - {D D.}_{1616 n no + + 99} - - {D D.}_{1616 n no + + 1010} - - \\ {D D.}_{1616 n no + + 1111} - - {D D.}_{1616 n no + + 1212} - - {D D.}_{1616 n no + + 1313} - - {D D.}_{1616 n no + + 1414} - - {D D.}_{1616 n no + + 1515} - - {D D.}_{1616 n no + + 1616} = = 88 {D D.}_{A A n no}^{λ λ 44},, n no = = 00,, 11,, 2...... 2...... \end{matrix}$

即分别得到8倍的波长λ1、λ2、λ3和λ4的光电容积脉搏波和而且完全消除了背景信号(包括各个波长抬高电平部分的作用)的影响。That is, the photoplethysmography waves with 8 times the wavelengths λ1, λ2, λ3 and λ4 are obtained respectively and Moreover, the background signal is completely eliminated (including the effect of raising the level of each wavelength) Impact.

得到各个波长的光电容积脉搏波，据此计算出λ1、λ2、λ3和λ4的光电容积脉搏波的谷值和峰值：I_minλ1、I_maxλ1、I_minλ2、I_maxλ2、I_minλ3、I_maxλ3、I_minλ4和I_maxλ4。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 .

再由I_minλ1、I_maxλ1、I_minλ2、I_maxλ2、I_minλ3、I_maxλ3、I_minλ4和I_maxλ4计算各个波长所对应的吸光度差值ΔA，可以得到由吸光度差值ΔA_λ1、ΔA_λ2……ΔA_λn组成的光谱值。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 .

本领域技术人员可以理解附图只是一个优选实施例的示意图，上述本发明实施例序号仅仅为了描述，不代表实施例的优劣。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.

以上所述仅为本发明的较佳实施例，并不用以限制本发明，凡在本发明的精神和原则之内，所作的任何修改、等同替换、改进等，均应包含在本发明的保护范围之内。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. A square wave modulated photoplethysmography measuring device for raising the level, characterized in that, the photoplethysmography measuring device comprises: a microprocessor, at least 2 kinds of light emitting diodes, a photosensitive device, a current/voltage conversion amplifiers and analog-to-digital converters,

The microprocessor outputs square waves with elevated levels at different frequencies and in a 2-fold ratio, and the square waves with elevated levels drive the at least two types of light-emitting diodes, and the light emitted by the light-emitting diodes is After the finger is measured, it is received by the photosensitive device, and 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;

The analog-to-digital converter converts the preset amplitude voltage signal into a digital signal, and the microprocessor processes the digital signal to obtain a photoplethysmogram and its valley and peak values, and through the valley and The peak value is obtained as a spectral value;

In the process of photoelectric signal collection by the photosensitive device, the noise level has not changed, but the square wave signal used as the drive has raised the preset level. In the low level part of the square wave signal, the square wave signal has improved compared with the noise. Obviously, the signal-to-noise ratio of the photoelectric signal obtained by the photosensitive device is improved in the low-level section of the square wave signal, thereby improving the accuracy of the digital signal input to the computer.

2. A kind of square-wave modulation photoplethysmography measuring device that raises level according to claim 1, is characterized in that, described as the square-wave signal of driving owing to raising preset level, in square-wave The high-level part of the signal improves the signal-to-noise ratio of the photoelectric signal obtained by the photosensitive device.

3. A kind of square-wave modulation photoplethysmography measuring device with raised level according to claim 1, characterized in that, the value of the preset level is more than half of the dynamic range of the photoelectric signal collected by the photosensitive device optimal.

4. A kind of square-wave modulation photoplethysmography measuring device with raised level according to claim 1, characterized in that, said microprocessor adopts any one of MCU, ARM, DSP or FPGA.

5. A method for measuring a square-wave modulated photoplethysmography measuring device for raising the level according to any one of claims 1 to 4, wherein the method comprises the following steps:

(1) The microprocessor drives at least two kinds of light-emitting diodes with square waves of different frequencies and raised levels in a 2-fold ratio;

(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 preset amplitude voltage signal 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.