CN104825152A - Single-path acquisition device for multiple paths of signals modulated by bioelectricity and square waves and method for single-path acquisition device - Google Patents
Single-path acquisition device for multiple paths of signals modulated by bioelectricity and square waves and method for single-path acquisition device Download PDFInfo
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Abstract
The invention discloses a single-path acquisition device for multiple paths of signals modulated by bioelectricity and square waves and a method for the single-path acquisition device. The acquisition device is used for acquiring N paths of biomedical signals through a single-path analog/digital converter, wherein the biomedical signals comprise high-frequency square waves loaded with PPG (Photoplethysmography) signals and a low-frequency bioelectric signal; a current signal is converted into a voltage signal with a preset amplitude by a current/voltage conversion amplifier; the bioelectric signal with a preset amplitude is obtained by a bioelectric signal detection circuit; the voltage signal with the preset amplitude and the bioelectric signal with the preset amplitude are added by an additive operation circuit to obtain a mixed signal; the mixed signal is converted into a digital signal by the single-path analog/digital converter; the digital signal is processed and separated by a microprocessor to obtain a modulated square wave signal and the low-frequency bioelectric signal; multiple paths of PPG signals can be demodulated from the modulated square wave signal. According to the single-path acquisition device and the method disclosed by the invention, synchronous acquisition of multiple paths of biomedical signals is realized by the single-path analog/digital converter; in addition, the single-path acquisition device and the single-path acquisition method have the characteristics of simple circuit, low cost and accurate measurement.
Description
Technical Field
The invention relates to the field of biomedical signal acquisition, in particular to a single-path acquisition device and method for modulating multi-path signals by bioelectricity and square waves.
Background
The voltage signal and other information-carrying variations are represented in their natural state in analog form, but are usually converted to digital signals by analog-to-digital converters for computer processing, transmission and storage, and thus in biomedical signal processing, analog-to-digital conversion is essential.
The inventor finds that in the process of realizing the invention, in the existing multi-path biomedical signal acquisition, a scheme of adopting a plurality of ADC or multi-path analog switches and matching a single ADC is usually adopted, and the former has the defects of complex circuit, high system power consumption and large circuit size; in the latter, switching noise is introduced due to switching of the multi-way switch during the acquisition process, and adjacent channel signals are interfered with each other due to the existence of the setup time of the multi-way switch.
Disclosure of Invention
The invention provides a single-path acquisition device and a single-path acquisition method for bioelectricity and square wave modulation multi-path signals, which realize analog-to-digital conversion on multi-path biomedical signals through a single-path analog-to-digital converter, and are described in detail as follows:
a single-channel collection device for modulating multiple signals with bioelectricity and square waves, the single-channel collection device comprising: the microprocessor outputs square waves with different frequencies and a 2-time ratio relation, the square waves drive at least 2 light emitting diodes, light emitted by the light emitting diodes is received by a photosensitive device after passing through a detected finger, the photosensitive device converts the light into a current signal, and the current signal is converted into a preset amplitude voltage signal through a current/voltage conversion amplifier;
the single-channel collection device further comprises: the low-frequency bioelectricity signal detection circuit comprises a low-frequency bioelectricity signal detection circuit, an addition operation circuit and a single-path analog-to-digital converter;
the low-frequency bioelectricity signal detection circuit acquires a preset amplitude bioelectricity signal, the preset amplitude voltage signal and the preset amplitude bioelectricity signal are added by the addition operation circuit to obtain a mixed signal, and the mixed signal is converted into a digital signal by the single-path analog-to-digital converter;
and the microprocessor processes the digital signal, separates out a modulation square wave signal and a low-frequency bioelectricity signal, and demodulates a PPG signal from the modulation square wave signal.
The low-frequency bioelectric signal specifically comprises: any one of ECG, EEG, EMG, EGG and EOG.
Wherein the addition operation circuit includes: one end of the first resistor is connected to a first signal source, one end of the second resistor is connected to a second signal source, and the other end of the first resistor and the other end of the second resistor are connected to a negative polarity input end of an operational amplifier; the positive polarity input end of the operational amplifier is connected with one end of a fourth resistor, and the other end of the fourth resistor is grounded; the negative polarity input end of the operational amplifier is also connected to one end of a third resistor, and the other end of the third resistor is connected to the output end of the operational amplifier to output signal voltage.
In another embodiment, the addition operation circuit includes: the circuit comprises a first resistor and a second resistor, wherein one end of the first resistor is connected to a first signal source, one end of the second resistor is connected to a second signal source, and the other end of the first resistor and the other end of the second resistor are connected to a positive-polarity input end of an operational amplifier; the negative polarity input end of the operational amplifier is simultaneously connected with one end of the third resistor and one end of the fourth resistor; the other end of the fourth resistor is grounded; the other end of the third resistor is connected with the output end of the operational amplifier to output signal voltage.
A method for acquisition of a single-pass acquisition device for bioelectrical and square-wave modulated multiplexed signals, the method comprising the steps of:
the mixed signal is converted into a digital signal by a single-path analog-to-digital converter and sent to a microprocessor;
the microprocessor carries out low-pass filtering processing on the digital signal to recover a low-frequency bioelectricity signal; the microprocessor separates and processes the digital signal to obtain a PPG signal and a bioelectricity signal, and background light interference in the PPG signal is eliminated;
respectively calculating a valley value and a peak value of the PPG signal; and then calculating the absorbance difference delta A corresponding to each wavelength according to the valley value and the peak value of the PPG signal, and obtaining a spectral value consisting of the absorbance difference delta A.
The microprocessor separates and processes the digital signal to obtain a PPG signal and a bioelectricity signal, and the step of eliminating the background light interference in the PPG signal specifically comprises the following steps:
assuming that the frequencies of the square wave signals output by the microprocessor to drive the light emitting diode 2 are respectively 8f, 4f, 2f and 1f, and the sampling frequency of the one-way analog-to-digital converter is fsAnd f iss16f and ensures intermediate sampling at the high and low levels of the highest frequency drive signal;
the number of the high and low level sampling points of the square wave signal is n, and the sampling points are the whole period of the lowest frequency signal; respectively solving the sum of the voltage amplitudes of n high-level sampling points and the sum of the voltage amplitudes of n low-level sampling points to obtain the difference value of the two voltage amplitude sums; the difference is n times the PPG signal; and eliminating the interference of background light and low-frequency bioelectricity signals to obtain a PPG signal.
The technical scheme provided by the invention has the beneficial effects that: the invention realizes analog-to-digital conversion on multi-path biomedical signals through the single-path analog-to-digital converter, and has the advantages of simple circuit, low cost and accurate measurement; when the addition operation circuit adopts the circuit designed by the invention, stable and high-precision mixing signals can be conveniently obtained, the integration is easy, the circuit cost is reduced, the dynamic range of the signals is expanded, and various requirements in practical application are met.
Drawings
FIG. 1 is a schematic structural diagram of a single-channel acquisition device for modulating multiple signals by bioelectricity and square waves;
FIG. 2 is a schematic diagram of an adder circuit;
FIG. 3 is a schematic diagram of another structure of the adder circuit;
figure 4 is a schematic diagram of the present invention providing separation of PPG signals of different wavelengths;
FIG. 5 is a flow chart of a single-channel acquisition method of bioelectricity and square wave modulated multi-channel signals.
In the drawings, the components represented by the respective reference numerals are listed below:
1: a microprocessor; 2: a light emitting diode;
3: a photosensitive device; 4: a current/voltage conversion amplifier;
5: a low-frequency bioelectric signal detection circuit; 6: an addition operation circuit;
7: a one-way analog-to-digital converter.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in further detail below.
Example 1
A single-channel acquisition device for modulating multiple signals by bioelectricity and square waves, referring to fig. 1, the single-channel acquisition device comprises: a microprocessor 1, at least 2 light emitting diodes 2, a photosensitive device 3, a current/voltage conversion amplifier 4, a low-frequency bioelectricity signal detection circuit 5, an addition operation circuit 6 and a single-path analog-to-digital converter 7,
the microprocessor 1 outputs square waves with different frequencies and a 2-time ratio relation, the square waves drive at least 2 light emitting diodes 2, light emitted by the light emitting diodes 2 is received by the photosensitive device 3 after passing through a finger to be detected, the photosensitive device 3 converts the light into a current signal, and the current signal is converted into a preset amplitude voltage signal through the current/voltage conversion amplifier 4.
The low-frequency bioelectricity signal detection circuit 5 acquires a preset amplitude bioelectricity signal, a preset amplitude voltage signal and the preset amplitude bioelectricity signal are added by the addition operation circuit 6 to obtain a mixed signal, the mixed signal is converted into a digital signal by the single-path analog-to-digital converter 7, the digital signal is processed by the microprocessor 1, a modulation square wave signal and the low-frequency bioelectricity signal are separated, and a PPG signal is demodulated from the modulation square wave signal.
Wherein, the number of the light emitting diodes 2 is more than or equal to 2. In specific implementation, the number of the light emitting diodes 2 is set according to the requirements in practical application; the preset amplitude voltage signal and the preset amplitude bioelectric signal are set according to the requirements in practical application, and in the specific implementation, the embodiment of the invention does not limit the preset amplitude voltage signal and the preset amplitude bioelectric signal.
Wherein the low frequency bioelectric signal comprises: any one of bioelectric signals such as ECG, EEG, EMG, EGG, EOG, etc. The microprocessor 1 may be any one of MCU, ARM, DSP or FPGA. The addition operation circuit 6 employs a commercially available conventional addition device.
Wherein the gain and bandwidth of the bioelectric signal detection circuit 5 are determined by the amplitude and frequency range of the detected bioelectric signal.
Example 2
A single-channel acquisition device for modulating multiple signals by bioelectricity and square waves, referring to fig. 1, the single-channel acquisition device comprises: the device comprises a microprocessor 1, at least 2 light emitting diodes 2, a photosensitive device 3, a current/voltage conversion amplifier 4, a low-frequency bioelectricity signal detection circuit 5, an addition operation circuit 6 and a single-path analog-to-digital converter 7. This embodiment is different from embodiment 1 in that the addition circuit 6 is implemented by using an addition circuit 6 designed according to an embodiment of the present invention, and referring to fig. 2, the addition circuit 6 includes: a first resistor R1And a second resistor R2，
A first resistor R1One end of the first signal source V is connected into1A second resistance R2One end of the first signal source is connected to a second signal source V2First resistance R1And the other end of the second resistor R2The other end of the operational amplifier A is connected with the negative polarity input end of the operational amplifier A; the positive polarity input end of the operational amplifier A is connected with the fourth resistor R4One terminal of (1), a fourth resistor R4The other end of the first and second electrodes is grounded; the negative input end of the operational amplifier A is also simultaneously connected with a third resistor R3One terminal of (1), a third resistor R3The other end of the signal line is connected with the output end of the operational amplifier A to output a signal voltage Vo。
First signal source V1A second signal source V2Respectively a preset amplitude voltage signal and a preset amplitude bioelectric signal; or, the first signal source V1A second signal source V2The preset amplitude bioelectric signal and the preset amplitude voltage signal are respectively; signal voltage VoIs a mixed signal.
Example 3
A single-channel acquisition device for modulating multiple signals by bioelectricity and square waves, referring to fig. 1, the single-channel acquisition device comprises: the device comprises a microprocessor 1, at least 2 light emitting diodes 2, a photosensitive device 3, a current/voltage conversion amplifier 4, a low-frequency bioelectricity signal detection circuit 5, an addition operation circuit 6 and a single-path analog-to-digital converter 7. This embodiment is different from embodiment 1 in that the addition circuit 6 can be implemented by using the addition circuit 6 designed in the embodiment of the present invention, and referring to fig. 3, the addition circuit 6 includes: a first resistor R1And a second resistor R2，
A first resistor R1One end of the first signal source V is connected into1A second resistance R2One end of the first signal source is connected to a second signal source V2First resistance R1And the other end of the second resistor R2The other end of the operational amplifier A is connected with the positive polarity input end of the operational amplifier A; the negative input end of the operational amplifier A is simultaneously connected with the third resistor R3And a fourth resistor R4One end of (a); a fourth resistor R4The other end of the first and second electrodes is grounded; third resistor R3The other end of the signal line is connected with the output end of the operational amplifier A to output a signal voltage Vo。
First signal source V1A second signal source V2Respectively a preset amplitude voltage signal and a preset amplitude bioelectric signal; or, the first signal source V1A second signal source V2The preset amplitude bioelectric signal and the preset amplitude voltage signal are respectively; signal voltage VoIs a mixed signal.
Example 4
A method for single-channel acquisition of bioelectrical and square-wave modulated multiplex signals, see fig. 4 and 5, comprising the steps of:
101: the mixed signal is converted into a digital signal by the one-way analog-to-digital converter 7 and sent to the microprocessor 1;
102: the microprocessor 1 carries out low-pass filtering processing on the digital signal to recover a low-frequency bioelectricity signal; the microprocessor 1 separates and processes the digital signal to obtain a PPG signal and a bioelectric signal, and the interference such as background light in the PPG signal is eliminated.
Wherein the steps are as follows:
1) assuming that the frequencies of the square wave signals output by the microprocessor 1 to drive the light emitting diode 2 are respectively 8f, 4f, 2f and 1f, and the sampling frequency of the one-way analog-to-digital converter 7 is fsAnd f iss16f and guarantees intermediate sampling at the high and low levels of the highest frequency (8f) drive signal;
2) the number of the high and low level sampling points of the square wave signal is n, the sampling points are the whole period of the lowest frequency (1f) signal, the sum of the voltage amplitudes of the n high level sampling points and the sum of the voltage amplitudes of the n low level sampling points are respectively solved, and the difference value of the sum of the two voltage amplitudes is obtained; the PPG signal (corresponding to the wavelength of the square wave) for which the difference is n times; and eliminating the interference of background light and low-frequency bioelectricity signals to obtain a PPG signal.
For the sake of simplicity, the light emitting diodes 2 with 4 wavelengths are taken as an example for explanation, and the driving square wave frequencies of the light emitting diodes with the wavelengths of λ 1, λ 2, λ 3 and λ 4 are assumed to be 8f, 4f, 2f and f, respectively.
Assume that the sampling frequency of the one-way analog converter 7 is fSAnd f isS2f and ensures intermediate sampling at λ 1 drive signal high and low levels.
Digital signal sequenceCan be expressed as:
wherein,andPPG signals at wavelengths λ 1, λ 2, λ 3 and λ 4 respectively,is a low-frequency signal and comprises: low-frequency bioelectric signals, background light, dark current of the photosensor 3, and offset voltage of the current/voltage conversion amplifier 4.
Assuming a sampling frequency fSThe amplitude of each path of square wave signal and the amplitude of the low-frequency signal are approximately considered to be unchanged in one period of the lowest driving signal frequency. Take the first 16 sample data as an example:
wherein,andthe amplitude of the PPG signal and the background signal at wavelengths λ 1, λ 2, λ 3, and λ 4, respectively.
In other words, the operation is performed sequentially every 16 digital signals:
that is, a PPG signal with 8 times wavelength lambda 1 is obtainedAnd completely eliminates low frequency signalsThe influence of (c).
That is, obtaining PPG signal with 8 times wavelength lambda 2And completely eliminates low frequency signalsThe influence of (c).
That is, 8 times of PPG signal with wavelength lambda 3 is obtainedAnd completely eliminates low frequency signalsThe influence of (c).
That is, 8 times of PPG signal with wavelength lambda 4 is obtainedAnd completely eliminates low frequency signalsThe influence of (c).
103: respectively calculating a valley value and a peak value of the PPG signal; then calculating the absorbance difference Delta A corresponding to each wavelength according to the valley value and the peak value of the PPG signal to obtain the difference Delta Aλ1、ΔAλ2……ΔAλnSpectral values of the composition.
The blood flow in the blood vessel changes periodically due to the pulsation of the artery, and the blood is a highly opaque liquid, so that the change in the pulse inevitably causes a change in the absorbance.
Considering the state of minimum arterial blood vessel filling degree, the incident light from the light source is not absorbed by the pulsating arterial blood, and the emergent light intensity I ismaxStrongest, incident light I, which can be regarded as pulsatile arterial blood; the state of the highest filling degree of the arterial blood vessels corresponds to the valley point of the photoelectric pulse wave, namely the moment of the maximum action of the pulsating arterial blood, and the emergent light intensity I at the momentminThe weakest is the minimum emergent light intensity I of the pulsating arterial blood. Therefore, the influence of all human body components with constant absorption characteristics, such as skin tissues, subcutaneous tissues and the like, on the absorbance can be eliminated by recording the absorbance values when the artery is filled to the maximum and when the artery is contracted to the minimum.
Let the incident light intensity be I0The detected light intensity when the artery is full and the detected light intensity when the artery is contracted are I respectivelyminAnd ImaxThen the difference between the absorbance when the artery is full and the absorbance when the artery is contracted is:
measuring the valley I of each photoplethysmogramminAnd peak value ImaxThe absorbance difference Delta A corresponding to the photoplethysmogram can be obtainedλ1、ΔAλ2……ΔAλnSpectral values of the composition.
That is, the valleys and peaks of the PPG signals at wavelengths λ 1, λ 2, λ 3, and λ 4 are calculated, respectively: i isminλ1、Imaxλ1、Iminλ2、Imaxλ2、Iminλ3、Imaxλ3、Iminλ4And Imaxλ4。
In the embodiment of the present invention, except for the specific description of the model of each device, the model of other devices is not limited, as long as the device can perform the above functions.
Those skilled in the art will appreciate that the drawings are only schematic illustrations of preferred embodiments, and the above-described embodiments of the present invention are merely provided for description and do not represent the merits of the embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (6)
1. A single-channel collection device for modulating multiple signals with bioelectricity and square waves, the single-channel collection device comprising: the microprocessor outputs square waves with different frequencies and a 2-time ratio relation, the square waves drive at least 2 light emitting diodes, light emitted by the light emitting diodes is received by a photosensitive device after passing through a detected finger, the photosensitive device converts the light into a current signal, and the current signal is converted into a preset amplitude voltage signal through a current/voltage conversion amplifier; it is characterized in that the preparation method is characterized in that,
the single-channel collection device further comprises: the low-frequency bioelectricity signal detection circuit comprises a low-frequency bioelectricity signal detection circuit, an addition operation circuit and a single-path analog-to-digital converter;
the low-frequency bioelectricity signal detection circuit acquires a preset amplitude bioelectricity signal, the preset amplitude voltage signal and the preset amplitude bioelectricity signal are added by the addition operation circuit to obtain a mixed signal, and the mixed signal is converted into a digital signal by the single-path analog-to-digital converter;
and the microprocessor processes the digital signal, separates out a modulation square wave signal and a low-frequency bioelectricity signal, and demodulates a PPG signal from the modulation square wave signal.
2. The single-path acquisition device for the bioelectricity and square-wave modulated multi-path signals according to claim 1, wherein the low-frequency bioelectricity signal is specifically: any one of ECG, EEG, EMG, EGG and EOG.
3. The single-channel signal acquisition device for bioelectricity and square wave modulation of multiple signals according to claim 1, wherein the addition operation circuit comprises: a first resistance and a second resistance, wherein the first resistance and the second resistance are connected,
one end of the first resistor is connected to a first signal source, one end of the second resistor is connected to a second signal source, and the other end of the first resistor and the other end of the second resistor are connected to a negative-polarity input end of the operational amplifier; the positive polarity input end of the operational amplifier is connected with one end of a fourth resistor, and the other end of the fourth resistor is grounded; the negative polarity input end of the operational amplifier is also connected to one end of a third resistor, and the other end of the third resistor is connected to the output end of the operational amplifier to output signal voltage.
4. The single-channel signal acquisition device for bioelectricity and square wave modulation of multiple signals according to claim 1, wherein the addition operation circuit comprises: a first resistance and a second resistance, wherein the first resistance and the second resistance are connected,
one end of the first resistor is connected to a first signal source, one end of the second resistor is connected to a second signal source, and the other ends of the first resistor and the second resistor are connected to a positive-polarity input end of an operational amplifier; the negative polarity input end of the operational amplifier is simultaneously connected with one end of the third resistor and one end of the fourth resistor; the other end of the fourth resistor is grounded; the other end of the third resistor is connected with the output end of the operational amplifier to output signal voltage.
5. A method for acquiring a single-channel acquisition device of bioelectrical and square-wave modulated multiplex signals according to any of claims 1 to 4, characterized in that it comprises the following steps:
the mixed signal is converted into a digital signal by a single-path analog-to-digital converter and sent to a microprocessor;
the microprocessor carries out low-pass filtering processing on the digital signal to recover a low-frequency bioelectricity signal; the microprocessor separates and processes the digital signal to obtain a PPG signal and a bioelectricity signal, and background light interference in the PPG signal is eliminated;
respectively calculating a valley value and a peak value of the PPG signal; and then calculating the absorbance difference delta A corresponding to each wavelength according to the valley value and the peak value of the PPG signal, and obtaining a spectral value consisting of the absorbance difference delta A.
6. The acquisition method according to claim 5, wherein the microprocessor performs separation processing on the digital signal to obtain a PPG signal and a bioelectric signal, and the step of eliminating the background light interference in the PPG signal specifically comprises:
assuming that the frequencies of the square wave signals output by the microprocessor to drive the light emitting diode 2 are respectively 8f, 4f, 2f and 1f, and the sampling frequency of the one-way analog-to-digital converter is fsAnd f iss16f and ensures intermediate sampling at the high and low levels of the highest frequency drive signal;
the number of the high and low level sampling points of the square wave signal is n, and the sampling points are the whole period of the lowest frequency signal; respectively solving the sum of the voltage amplitudes of n high-level sampling points and the sum of the voltage amplitudes of n low-level sampling points to obtain the difference value of the two voltage amplitude sums; the difference is n times the PPG signal; and eliminating the interference of background light and low-frequency bioelectricity signals to obtain a PPG signal.
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| CN111398794A (en) * | 2020-03-31 | 2020-07-10 | 苏州汇川技术有限公司 | Digital quantity input signal detection circuit and elevator controller |
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| CN116112107B (en) * | 2023-04-13 | 2023-09-08 | 深圳市奋达智能技术有限公司 | Multi-PD signal selection method and related equipment thereof |
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