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 photoelectric volume pulse wave measuring device and a measuring method thereof. A microprocessor outputs orthogonal square waves with different frequencies; the orthogonal square waves drive at least two light emitting diodes; light emitted by the light emitting diodes is received by a photosensitive device after passing through a measured finger; the photosensitive device converts the light into a voltage signal which is converted into a preset-amplitude voltage signal by a current/voltage conversion amplifier; an analog-digital converter converts the preset-amplitude voltage signal into a digital signal; and the microprocessor processes the digital signal, acquires photoelectric volume pulse waves and a valley value and a peak value thereof, and obtains a spectrum value by the valley value and the peak value. The measuring method comprises the following steps: the microprocessor separates the digital signal to obtain the photoelectric volume pulse waves and eliminate the interference of background light; the valley value and the peak value are acquired according to the photoelectric volume pulse wave; and an absorbance difference is obtained by calculating the valley value and the peak value, and the spectrum value is acquired by the absorbance difference. The orthogonal-square-wave-modulation photoelectric volume pulse wave measuring device and the measuring method thereof have the characteristics that the measurement is accurate and the circuit is simple.

Description

A kind of quadrature square wave modulated photoelectric volume pulse wave device and measuring method

Technical field

The present invention relates to a kind of quadrature square wave modulated photoelectric volume pulse wave device and measuring method.

Background technology

Photoelectricity volume pulsation wave (Photo Plethysmo Graphy, hereinafter to be referred as PPG) is a kind of important physiological signal, is widely used in the cardiovascular system blood constituent analysis of unifying.As to adopting 2 kinds or LED of more than two kinds (light emitting diode) measure PPG and realize in the measurement of blood oxygen saturation.The common interference that adopts time division way to gather PPG and eliminate bias light in these are measured.

Inventor finds in realizing process of the present invention, at least has following shortcoming and defect in prior art:

The shortcomings such as the measuring method of existing multi-wavelength PPG exists that circuit structure is complicated, device and technological requirement is high, debug difficulties, reliability is low, amount of calculation is large and result is not accurate enough.

Summary of the invention

The technical problem to be solved in the present invention is to provide a kind of quadrature square wave modulated photoelectric volume pulse wave device and measuring method, this measuring device and measuring method can realize high-acruracy survey, and circuit structure is simple, device and technological requirement is low, debugging easily, the advantage such as reliability is high, amount of calculation is little, described below:

The invention provides a kind of quadrature square wave modulated photoelectric volume pulse wave device, described photoelectricity volume pulse wave measuring apparatus comprises: microprocessor, at least 2 kinds of light emitting diodes, light-sensitive device, current/voltage-converted amplifier and analog-digital converters,

The quadrature square wave of described microprocessor output different frequency, the at least described 2 kinds of light emitting diodes of described quadrature square wave drive, the light that described light emitting diode sends is received by described light-sensitive device after tested finger, described light-sensitive device converts voltage signal to, described voltage signal converts default amplitude voltage signal to through described current/voltage-converted amplifier, described analog-digital converter converts described default amplitude voltage signal to digital signal, described microprocessor is processed described digital signal, obtain photoelectricity volume pulsation wave and valley thereof and peak value, by described valley and described peak value, obtain spectral value.

Described microprocessor adopts any one in MCU, ARM, DSP or FPGA.

The invention provides a kind of quadrature square wave modulated photoelectric volume pulse wave method, said method comprising the steps of:

(1) microprocessor adopts at least 2 kinds of light emitting diodes of quadrature square wave drive of different frequency;

(2) light that described light emitting diode sends is received and is converted to voltage signal by light-sensitive device after tested finger, and described voltage signal zooms into the voltage signal of default amplitude through current/voltage-converted amplifier;

(3) described default amplitude voltage signal converts digital signal to through analog-digital converter and sends into described microprocessor;

(4) described microprocessor carries out to described digital signal the interference that separating treatment obtains photoelectricity volume pulsation wave and eliminates bias light;

(5) according to described photoelectricity volume pulsation wave, obtain valley and peak value;

(6) described valley and described peak value are calculated to absorbance difference, by described absorbance difference, obtain spectral value.

A kind of quadrature square wave modulated photoelectric volume pulse wave device provided by the invention and measuring method, compared with prior art have advantages of as follows:

The present invention is according to Lambert-Beer's law, adopt quadrature square wave division modulation and digital demodulation techniques to design a kind of photoelectricity volume pulsation wave and valley and peak value of quadrature square-wave frequency modulation multi-wave length illuminating diode, by valley and peak value, obtain device and the measuring method of spectral value, have measure accurately, circuit is simple, without debugging, good manufacturability and feature with low cost.

Accompanying drawing explanation

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

Fig. 2 is the structural representation of a kind of quadrature square wave modulated photoelectric volume pulse wave device provided by the invention;

Fig. 3 is the schematic diagram of separated different wavelengths of light Power Capacity pulse wave provided by the invention;

Fig. 4 is the flow chart of a kind of quadrature square wave modulated photoelectric volume pulse wave method provided by the invention;

Fig. 5 is another structural representation of a kind of quadrature square wave modulated photoelectric volume pulse wave device provided by the invention.

In accompanying drawing, the list of parts of each label representative is as follows:

1: microprocessor; 2: light emitting diode;

3: light-sensitive device; 4: current/voltage-converted amplifier;

5: analog-digital converter; PX.1:I/O mouth;

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

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

R1: the first resistance; VCC: power supply;

R2: the second resistance; R3: the 3rd resistance;

R4: the 4th resistance; R5: the 5th resistance;

R6: the 6th resistance; C1: the first electric capacity;

C2: the second electric capacity; D1: the first light emitting diode;

D2: the second light emitting diode; D3: the 3rd light emitting diode;

D4: the 4th light emitting diode; A1: operational amplifier;

PY mouth: I/O.

The specific embodiment

For making the object, technical solutions and advantages of the present invention clearer, below in conjunction with accompanying drawing, embodiment of the present invention is described further in detail.

Due to the pulsation phenomenon of tremulous pulse, make blood flow in blood vessel be cyclically-varying, and blood is height opaque liquid, so the pulse variation of beating must cause the variation of absorbance, as shown in Figure 1.

Consider arteries fullness degree minimum state, from the incident illumination of light source, by pulsation arterial blood, do not absorbed output intensity I now _maxthe strongest, can be considered pulsation arterial blood incident illumination I; And the valley point of the corresponding photoelectricity pulse wave of the high state of arteries fullness degree, the moment of the arterial blood effect maximum of pulsing, output intensity I now _minthe most weak, be the minimum output intensity I of pulsation arterial blood.So, by recording tremulous pulse, filling the absorbance being contracted to hour to maximum and tremulous pulse, all have the human body component of constant absorption feature for the impact of absorbance just can to eliminate skin histology, subcutaneous tissue etc.

According to the Lambert-Beer's law of revising, establish I ₀, I is respectively incident intensity and output intensity, α is molecular extinction coefficient, c is each constituent concentration, l is the mean optical pathlength of light in tissue, G is the light loss being caused by scattering, absorbance A can be expressed as:

$A=-\lg \frac{I}{I_0}=-2.303\mathrm{\αcl}+G---\left(1\right)$

If the absorptance of biological tissue is μ _a, μ _a=α c, substitution formula (1) can obtain:

A＝-2.303μ _al+G (2)

In light transmission detects, absorbance mainly consists of the absorption and the scattering that are transmitted tissue, and wherein blood scattering is relatively little, can ignore.Like this, G is only contributed by the tissue except pulsation arterial blood, in measuring process, remains unchanged.If the tissue that is transmitted except pulsation arterial blood is total to n layer, the absorptance of i layer is μ _ti, the absorptance of arterial blood is μ _ab, when in a photoelectricity pulse wave cycle, tremulous pulse is full, maximum optical path length is l _max, minimum optical path length when tremulous pulse shrinks is l _min, absorbance A when tremulous pulse is full ₁absorbance A while shrinking with tremulous pulse ₂can be expressed as:

$A_1=-2.303\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\μ}}_{\mathrm{ti}}{l}_{\max }-2.303{\mathrm{\μ}}_{\mathrm{ab}}{l}_{\max }+G---\left(3\right)$

$A_2=-2.303\underset{i=1}{\overset{n}{\mathrm{\Σ}}}{\mathrm{\μ}}_{\mathrm{ti}}{l}_{\min }-2.303{\mathrm{\μ}}_{\mathrm{ab}}{l}_{\min }+G---\left(4\right)$

If l is l _maxwith l _minpoor.Due to basicly stable except pulsation its hetero-organization arterial blood, do not carry out cycle variation, so this part at tremulous pulse full and while shrinking on not impact of absorbance, first component in formula (3) and formula (4) is equal.The difference of absorbance when absorbance when tremulous pulse is full and tremulous pulse shrink is:

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

In superincumbent derivation, non-pulsatile blood and the absorption of each layer tissue and the absorbance component of scattering have all been disappeared, absorbance difference Δ A when tremulous pulse is full and when tremulous pulse shrinks is only contributed by the pulsation absorption portion of arterial blood, the Change of absorption of the arterial blood of main reflection pulsation.Be equivalent in itself in being transmitted tissue, the impact of its hetero-organization except pulsation arterial blood such as skin, muscle and venous blood has all been removed, only leave pure pulsation arterial blood and partly carry out the measurement of absorbance difference Δ A.So, the impact of the individual variation such as skin, skeleton and muscle has all been removed.

If incident intensity is I ₀, tremulous pulse detects light intensity while detecting light intensity and tremulous pulse contraction when full and is respectively I _minand I _max, absorbance difference Δ A when absorbance when tremulous pulse is full and tremulous pulse shrink is:

$\mathrm{\ΔA}=A_1-A_2=\lg \left(\frac{I_0}{I_{\min }}\right)-\lg \left(\frac{I_0}{I_{\max }}\right)=\lg \left(\frac{I_{\max }}{I_{\min }}\right)---\left(6\right)$

Measure the valley I of each photoelectricity volume pulsation wave _minand peak I _maxcan obtain the corresponding absorbance difference Δ of photoelectricity volume pulsation wave A, can obtain by Δ A _{λ 1}, Δ A _{λ 2}Δ A _{λ n}the spectral value forming.

A quadrature square wave modulated photoelectric volume pulse wave device, referring to Fig. 2, this photoelectricity volume pulse wave measuring apparatus comprises: 1, at least 2 kinds of light emitting diodes 2 of microprocessor, light-sensitive device 3, current/voltage-converted amplifier 4 and analog-digital converter 5.

The quadrature square wave of microprocessor 1 output different frequency, at least 2 kinds of light emitting diodes of quadrature square wave drive 2, the light that light emitting diode 2 sends is received by light-sensitive device 3 after tested finger, light-sensitive device 3 converts voltage signal to, voltage signal converts default amplitude voltage signal to through current/voltage-converted amplifier 4, analog-digital converter 5 will be preset amplitude voltage signal and convert digital signal to, 1 pair of digital signal of microprocessor is processed, obtain photoelectricity volume pulsation wave and valley thereof and peak value, by valley and peak value, obtain spectral value.

Wherein, the quantity of light emitting diode 2 is more than or equal to 2.During specific implementation, the quantity of light emitting diode 2 is set according to the needs in practical application, and the embodiment of the present invention does not limit this.

Wherein, default amplitude is set according to the needs in practical application, and during specific implementation, the embodiment of the present invention does not limit this.

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

A quadrature square wave modulated photoelectric volume pulse wave method, referring to Fig. 3 and Fig. 4, the method comprises the following steps:

101: microprocessor 1 adopts at least 2 kinds of light emitting diodes of quadrature square wave drive 2 of different frequency;

102: the light that light emitting diode 2 sends is received and converted to voltage signal by light-sensitive device 3 after tested finger, and voltage signal zooms into default amplitude voltage signal through current/voltage-converted amplifier 4;

103: default amplitude voltage signal converts digital signal to through analog-digital converter 5 and sends into microprocessor 1;

104: 1 pair of digital signal of microprocessor carries out the interference that separating treatment obtains photoelectricity volume pulsation wave and eliminates bias light;

105: according to photoelectricity volume pulsation wave, obtain valley and peak value;

For the purpose of concise explanation, the light emitting diode 2 of 4 kinds of wavelength of take describes as example, the light emitting diode 2 driving quadrature square wave frequencies of supposing λ 1 (D1 light emitting diode) and λ 2 (D2 light emitting diode) wavelength are 2 times of f, the light emitting diode 2 of λ 3 (D3 light emitting diode) and λ 4 (D4 light emitting diode) wavelength drives quadrature square wave frequency to be respectively 1 times of f, and 90 ° of identical but phase phase difference of the driving quadrature square wave frequency of the light emitting diode 2 of λ 1, λ 2 wavelength, 90 ° of the identical but phase phase difference of the driving quadrature square wave frequency of the light emitting diode 2 of λ 3, λ 4 wavelength.

The sample frequency of supposing analog-digital converter 5 is f _s, and f _s=2f also guarantees to drive the high and low level intermediate samples of signal at λ 1.

Digital signal sequences

can be expressed as:

$D_i^t=D_i^{\mathrm{\λ}1}+D_i^{\mathrm{\λ}2}+D_i^{\mathrm{\λ}3}+D_i^{\mathrm{\λ}4}+D_i^B---\left(7\right)$

Wherein,

with be respectively the photoelectricity volume pulsation wave of wavelength X 1, λ 2, λ 3 and λ 4,

for the dark current of bias light and light-sensitive device 3, the summation signals of the offset voltage of current/voltage-converted amplifier 4 (abbreviation background signal).

Suppose sample frequency f _sfar above the change frequency of modulation orthogonal square-wave signal and bias light, the one-period of minimum driving signal frequency can be similar to think the amplitude of each road quadrature square-wave signal and the amplitude of bias light signal constant.The most front 8 sampled values of take are example:

$\left\{\begin{array}{c}{D}_1^{\mathrm{\λ}1}=D_2^{\mathrm{\λ}1}=D_5^{\mathrm{\λ}1}=D_6^{\mathrm{\λ}1}=D_A^{\mathrm{\λ}1}\\ D_3^{\mathrm{\λ}1}=D_4^{\mathrm{\λ}1}=D_7^{\mathrm{\λ}1}=D_8^{\mathrm{\λ}1}=0\\ D_1^{\mathrm{\λ}2}=D_4^{\mathrm{\λ}2}=D_5^{\mathrm{\λ}2}=D_8^{\mathrm{\λ}2}=D_A^{\mathrm{\λ}2}\\ D_2^{\mathrm{\λ}2}=D_3^{\mathrm{\λ}3}=D_6^{\mathrm{\λ}2}=D_7^{\mathrm{\λ}2}=0\\ D_1^{\mathrm{\λ}3}=D_2^{\mathrm{\λ}3}=D_3^{\mathrm{\λ}3}=D_4^{\mathrm{\λ}3}=D_A^{\mathrm{\λ}3}\\ D_5^{\mathrm{\λ}3}=D_6^{\mathrm{\λ}3}=D_7^{\mathrm{\λ}3}=D_8^{\mathrm{\λ}3}=0\\ D_1^{\mathrm{\λ}4}=D_2^{\mathrm{\λ}4}=D_7^{\mathrm{\λ}4}=D_8^{\mathrm{\λ}4}=D_A^{\mathrm{\λ}4}\\ D_3^{\mathrm{\λ}4}=D_4^{\mathrm{\λ}4}=D_5^{\mathrm{\λ}4}=D_6^{\mathrm{\λ}4}=0\\ D_1^B=D_2^B=D_3^B=D_4^B=D_5^B=D_6^B=D_7^B=D_8^B=D_A^B\end{array}\right.---\left(8\right)$

Wherein,

with be respectively wavelength X 1, λ 2, λ 3 and the optical signal of λ 4 and the amplitude of background signal.

In other words, take every 8 digital signals of order carries out computing as one group:

$D_{8n+1}+D_{8n+2}-D_{8n+3}-D_{8n+4}+D_{8n+5}+D_{8n+6}-D_{8n+7}-D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}1}$ n＝0，1，2......(9)

Obtain the photoelectricity volume pulsation wave of the wavelength X 1 of 4 times

and eliminated background signal completely

impact.

$D_{8n+1}-D_{8n+2}-D_{8n+3}+D_{8n+4}+D_{8n+5}-D_{8n+6}-D_{8n+7}+D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}2}$ n＝0，1，2......(10)

Obtain the photoelectricity volume pulsation wave of the wavelength X 2 of 4 times

and eliminated background signal completely

impact.

$D_{8n+1}+D_{8n+2}+D_{8n+3}+D_{8n+4}-D_{8n+5}-D_{8n+6}-D_{8n+7}-D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}3}$ n＝0，1，2......(11)

Obtain the photoelectricity volume pulsation wave of the wavelength X 3 of 4 times and eliminated background signal completely

impact.

$D_{8n+1}+D_{8n+2}-D_{8n+3}-D_{8n+4}-D_{8n+5}-D_{8n+6}+D_{8n+7}+D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}4}$ n＝0，1，2......(12)

Obtain the photoelectricity volume pulsation wave of the wavelength X 4 of 4 times

and eliminated background signal completely

impact.

Calculate respectively photoelectricity volume pulsation wave valley and the peak value of wavelength X 1, λ 2, λ 3 and λ 4: I _{min λ 1}, I _{max λ 1}, I _{min λ 2}, I _{max λ 2}, I _{min λ 3}, I _{max λ 3}, I _{min λ 4}and I _{max λ 4};

106: valley and peak value are calculated to absorbance difference, by absorbance difference, obtain spectral value.

Adopt formula (6) to calculate each absorbance difference Δ A _{λ 1}, Δ A _{λ 2}... Δ A _{λ n}, and form spectral value by absorbance difference.

As shown in Figure 5, a kind of quadrature square wave modulated photoelectric volume pulse wave device has adopted 4 kinds of light emitting diodes 2, four I/O mouth PX.1 of microprocessor 1, PX.2, PX.3 and PX.4 are respectively by the first resistance R 1, the second resistance R 2, the 3rd resistance R 3 and the 4th resistance R 4 drive the first light emitting diode D1, the second light emitting diode D2, the 3rd light emitting diode D3 and the 4th light emitting diode D4, the first light emitting diode D1, the second light emitting diode D2, the tested finger of light printing opacity that the 3rd light emitting diode D3 and the 4th light emitting diode D4 send is received by light sensor 3, and the signal process that light sensor 3 receives is by operational amplifier A 1, the first capacitor C 1, the second capacitor C 2, the current/voltage-converted amplifier 4 that the 5th resistance R 5 and the 6th resistance R 6 form converts default amplitude voltage signal to, and then analog-digital converter 5 will be preset amplitude voltage signal with two times of speed of the highest driven for emitting lights diode 2 frequencies and convert digital signal to and be sent to microprocessor 1 by PY mouth.Digital signal is first isolated different wavelengths of light Power Capacity pulse wave signal at microprocessor 1: 8 digital signals that every order is obtained are one group, according to

$D_{8n+1}+D_{8n+2}-D_{8n+3}-D_{8n+4}+D_{8n+5}+D_{8n+6}-D_{8n+7}-D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}1}$ n＝0，1，2......

$D_{8n+1}-D_{8n+2}-D_{8n+3}+D_{8n+4}+D_{8n+5}-D_{8n+6}-D_{8n+7}+D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}2}$ n＝0，1，2......

$D_{8n+1}+D_{8n+2}+D_{8n+3}+D_{8n+4}-D_{8n+5}-D_{8n+6}-D_{8n+7}-D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}3}$ n＝0，1，2......

$D_{8n+1}+D_{8n+2}-D_{8n+3}-D_{8n+4}-D_{8n+5}-D_{8n+6}+D_{8n+7}+D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}4}$ n＝0，1，2......

Obtain respectively the photoelectricity volume pulsation wave of wavelength X 1, λ 2, λ 3 and the λ 4 of 4 times

with

and eliminated background signal completely

impact.

Obtain the photoelectricity volume pulsation wave of each wavelength, calculate accordingly valley and the peak value of the photoelectricity volume pulsation wave of λ 1, λ 2, λ 3 and λ 4: I _{min λ 1}, I _{max λ 1}, I _{min λ 2}, I _{max λ 2}, I _{min λ 3}, I _{max λ 3}, I _{min λ 4}and I _{max λ 4}.

Again by I _{min λ 1}, I _{max λ 1}, I _{min λ 2}, I _{max λ 2}, I _{min λ 3}, I _{max λ 3}, I _{min λ 4}and I _{max λ 4}calculate the corresponding absorbance difference Δ of each wavelength A, can obtain by absorbance difference Δ A _{λ 1}, Δ A _{λ 2}Δ A _{λ n}the spectral value forming.

In sum, the embodiment of the present invention provides a kind of quadrature square wave modulated photoelectric volume pulse wave device and measuring method, the embodiment of the present invention is according to Lambert-Beer's law, adopt quadrature square wave division modulation and digital demodulation techniques to design a kind of photoelectricity volume pulsation wave and valley and peak value of quadrature square-wave frequency modulation multi-wave length illuminating diode, by valley and peak value, obtain device and the measuring method of spectral value, have measure accurately, circuit is simple, without debugging, good manufacturability and feature with low cost.

It will be appreciated by those skilled in the art that accompanying drawing is the schematic diagram of a preferred embodiment, the invention described above embodiment sequence number, just to describing, does not represent the quality of embodiment.

The foregoing is only preferred embodiment of the present invention, in order to limit the present invention, within the spirit and principles in the present invention not all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.

Claims (1)

1. a measuring method for quadrature square wave modulated photoelectric volume pulse wave device, is characterized in that, said method comprising the steps of:

(1) microprocessor adopts at least 2 kinds of light emitting diodes of quadrature square wave drive of different frequency;

(2) light that described light emitting diode sends is received and is converted to voltage signal by light-sensitive device after tested finger, and described voltage signal zooms into the voltage signal of default amplitude through current/voltage-converted amplifier;

(3) described default amplitude voltage signal converts digital signal to through analog-digital converter and sends into described microprocessor;

(4) described microprocessor carries out to described digital signal the interference that separating treatment obtains photoelectricity volume pulsation wave and eliminates bias light;

(5) according to described photoelectricity volume pulsation wave, obtain valley and peak value;

(6) described valley and described peak value are calculated to absorbance difference, by described absorbance difference, obtain spectral value;

Wherein, the described step of obtaining valley and peak value according to described photoelectricity volume pulsation wave is specially:

It is 2 times of f that the light emitting diode of λ 1 and λ 2 wavelength drives quadrature square wave frequency, it is 1 times of f that the light emitting diode of λ 3 and λ 4 wavelength drives quadrature square wave frequency, 90 ° of the identical but phase phase difference of the driving quadrature square wave frequency of the light emitting diode of λ 1, λ 2 wavelength, 90 ° of the identical but phase phase difference of the driving quadrature square wave frequency of the light emitting diode of λ 3, λ 4 wavelength; The sample frequency of analog-digital converter is f _s, and f _s=2f;

Digital signal sequences

be expressed as:

$D_i^t=D_i^{\mathrm{\λ}1}+D_i^{\mathrm{\λ}2}+D_i^{\mathrm{\λ}3}+D_i^{\mathrm{\λ}4}+D_i^B$

Wherein,

with

be respectively the photoelectricity volume pulsation wave of wavelength X 1, λ 2, λ 3 and λ 4,

for the dark current of bias light and light-sensitive device, the summation signals of the offset voltage of current/voltage-converted amplifier; Sample frequency f _sfar above the change frequency of modulation orthogonal square-wave signal and bias light, the one-period of minimum driving signal frequency think the amplitude of each road quadrature square-wave signal and the amplitude of bias light signal constant:

$\left\{\begin{array}{c}{D}_1^{\mathrm{\λ}1}=D_2^{\mathrm{\λ}1}=D_5^{\mathrm{\λ}1}=D_6^{\mathrm{\λ}1}=D_A^{\mathrm{\λ}1}\\ D_3^{\mathrm{\λ}1}=D_4^{\mathrm{\λ}1}=D_7^{\mathrm{\λ}1}=D_8^{\mathrm{\λ}1}=0\\ D_1^{\mathrm{\λ}2}=D_4^{\mathrm{\λ}2}=D_5^{\mathrm{\λ}2}=D_8^{\mathrm{\λ}2}=D_A^{\mathrm{\λ}2}\\ D_2^{\mathrm{\λ}2}=D_3^{\mathrm{\λ}2}=D_6^{\mathrm{\λ}2}=D_7^{\mathrm{\λ}2}=0\\ D_1^{\mathrm{\λ}3}=D_2^{\mathrm{\λ}3}=D_3^{\mathrm{\λ}3}=D_4^{\mathrm{\λ}3}=D_A^{\mathrm{\λ}3}\\ D_5^{\mathrm{\λ}3}=D_6^{\mathrm{\λ}3}=D_7^{\mathrm{\λ}3}=D_8^{\mathrm{\λ}3}=0\\ D_1^{\mathrm{\λ}4}=D_2^{\mathrm{\λ}4}=D_7^{\mathrm{\λ}4}=D_8^{\mathrm{\λ}4}=D_A^{\mathrm{\λ}4}\end{array}\right.$

$D_3^{\mathrm{\λ}4}=D_4^{\mathrm{\λ}4}=D_5^{\mathrm{\λ}4}=D_6^{\mathrm{\λ}4}=0$

$D_1^B=D_2^B=D_3^B=D_4^B=D_5^B=D_6^B=D_7^B=D_8^B=D_A^B$

Wherein, with

be respectively wavelength X 1, λ 2, λ 3 and the optical signal of λ 4 and the amplitude of background signal;

Every 8 digital signals are one group and carry out computing in order:

$\begin{array}{cc}{D}_{8n+1}+D_{8n+2}-D_{8n+3}-D_{8n+4}+D_{8n+5}+D_{8n+6}-D_{8n+7}-D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}1}& n=\mathrm{0,1,2}......\end{array}$

Obtain the photoelectricity volume pulsation wave of the wavelength X 1 of 4 times

and eliminated background signal completely

impact;

$\begin{array}{cc}{D}_{8n+1}-D_{8n+2}-D_{8n+3}+D_{8n+4}+D_{8n+5}-D_{8n+6}-D_{8n+7}+D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}2}& n=\mathrm{0,1,2}......\end{array}$

Obtain the photoelectricity volume pulsation wave of the wavelength X 2 of 4 times

and eliminated background signal completely

impact;

$\begin{array}{cc}{D}_{8n+1}+D_{8n+2}+D_{8n+3}+D_{8n+4}-D_{8n+5}-D_{8n+6}-D_{8n+7}-D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}3}& n=\mathrm{0,1,2}......\end{array}$

Obtain the photoelectricity volume pulsation wave of the wavelength X 3 of 4 times and eliminated background signal completely

impact;

$\begin{array}{cc}{D}_{8n+1}+D_{8n+2}-D_{8n+3}-D_{8n+4}-D_{8n+5}-D_{8n+6}+D_{8n+7}+D_{8n+8}={4D}_{\mathrm{An}}^{\mathrm{\λ}4}& n=\mathrm{0,1,2}......\end{array}$

Obtain the photoelectricity volume pulsation wave of the wavelength X 4 of 4 times

and eliminated background signal completely

impact;

Calculate respectively photoelectricity volume pulsation wave valley and the peak value of wavelength X 1, λ 2, λ 3 and λ 4: I _{min λ 1}, I _{max λ 1}, I _{min λ 2}, I _{max λ 2}, I _{min λ 3}, I _{max λ 3}, I _{min λ 4}and I _{max λ 4}.

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