[introduction] receiver of compositive and optical front is aimed at pulse blood oxygen to measure especially in medical treatment equipment and nurse the dot detects immediately (in the application such as PoC) , having extensive use. Oxygen of blood of article introduction pulse is measured application and nurse the dot detects immediately (PoC) application, the function of optical front asks, come the advantage of receiver of derivative and compositive optical front.

01 optical front are diagnosed outside body (the applied example in IVD) system

Oxygen of 1.1 pulse blood measures application

The Covid-19 2020 brought the Fan Shi of healthy world to transform. Different age paragraph the life style that the person dogs ceaselessly now and monitors them is asked for, degree of saturation of the oxygen that be like blood (SpO2) , heartbeat (HR) and VOx level, this is them the one part of daily way of life.

Pulse blood oxygen measures a principle:

Pulse blood oxygen is measured is one kind closes without achieved hematic oxygen (SpO2) measurement technique. This kind is measured is the technology that is based on a kind to be called PPG(Photoplethysmography) . This kind of technology can divide be transmission type or reflex type:

● Measure in oxygen of blood of transmission type pulse in, photoelectricity diode and (glow diode) LED is placed respectively in human body relative to two side (for example finger) . Human body organization absorbs partial light, and photoelectricity diode collects the odd light that passes human body.

● In reflexing appearance of oxygen of type pulse blood, photoelectricity diode and LED are in same side. The photoelectricity diode here collects catoptric of skin lower part smooth.

Graph 1. The transmission formula that is used at pulse blood oxygen to measure (left) and reflex type (right) technology (picture origin ADI)

Hematic oxygen measures pulse to basically be based on 3 principles:

● Blood of arteries and veins of beating of arteries and veins is right transmission / the absorbance of reflex.

● HbO2 and RHb are long to different light-wave (glow Vs is infra-red smooth) different absorbance feature.

● Transmission / the direct dependency between reflex and the PPG signal electricity that photoelectricity diode produces.

1.2 fluorescence detect application

In be based on fluorescence to detect in the IVD test of diagnostic technology, contain the example of fluorescent label to be aroused by the light of specific wavelengh, if pursue,2 medium green arrowhead are shown. If interested analytic substance is contained in example, fluorescent label can pass the light that shoots feebleminded class to react to inspiring generation.

For example, in the graph 2 in, the fluorescent label in example has reaction through firing infrared ray. This kind of light that give out needs detected fluorescent signal namely, in order to determine the presence of content of the analysis in example, the likelihood still has an amount.

Graph 2. IVD fluorescent testing system

The diagnostic test that is based on fluorescence will have a threshold value that is considered as reportable fluorescence. Under the fluorescent signal of threshold value level, the existence in cannot making clear example certainly is analysed content.

The electronic component in diagnostic testing instrument, with etc element, can cause background noise, force threshold watch thereby tall.

To reduce threshold value level, be in thereby better sensitivity is not obtained below the circumstance with alternative sacrifice, need designs optical testing system carefully, in order to ensure signal catenary won’t create background noise level.

The function of 02 optical front asks

We diagnose citing of fluorescent testing system with typical PoC.

Use glow diode (LED) will arise arouse light, use photoelectricity diode (PD) will detect the fluorescence that comes from example blasts off. PD generation and electric current of proportionate of fluorescent signal intensity, this electric current may be very faint. Opposite at background noise, PD electric current is not normally constant small, the electronic design with careful need detects with realizing tall sensitivity and do not sacrifice alternative.

Graph 3. Typical PoC diagnoses fluorescent testing system

Graph the main element of the 3 PoC fluorescent testing system that showed a pattern. The voltaic signal that comes from PD is crossed block amplifier (TIA) changeover becomes voltage signal. Voltage signal by modulus converter (ADC) digitlize and change into corresponding fluorescent level.

Need is in the design personnel of PoC system not to sacrifice as far as possible the diagnostic sensitivity with the highest implementation below alternative circumstance. Accordingly, raised the function requirement to optical front:

● Answer LED excitation to identify low-down PD electric current reliably

About PoC system, if where not to sacrifice,the greatest diagnostic sensitivity comes true below alternative circumstance, translate into of this one target answers LED excitation to identify the requirement of low-down PD electric current reliably. For example, tall sensitivity system must detect when the LED drive electric current that can answering class of 100 MA amount the PD electric current that measures level to Pi Anpei. That is to say, in give about below the circumstance of the optical attenuation of 140 DB, system must can detect PD is fluorescent.

Want to achieve such performance, must combine electron and the consideration that the system designs a respect.

● The imitate front of PD (AFE) design is weighed particularly should.

Because PD report is current constant opposite at background noise very weak, TIA needs to have tall gain and low input to slant buy electric current. Other and important parameter is the least space between bias voltage of low TIA input and PD and TIA.

● The system designs tall to coming true sensitivity to detect also is very important.

Fluorescence detects must arouse synchronism with LED, because this needs a controller,will ensure this is planted synchronous sex. To identify signal of faint PD electric current from background noise, normally need is begged to many fluorescent reading average. This kind of average technology is a of systematic controller main function. The drift in ambient light and LED illume can cause systematic error. The controller that allow to reject ambient light and affects adrift in consideration LED illume can achieve advantage of integral system performance.

The advantage of 03 compositive and optical front

Read for PoC take implement when designing signal catenary, two kinds of different frameworks choose: ? The complete disperse solution that Bin? place shows or use compositive and optical front, if pursue,3 are shown.

Graph 4. Use the PoC testing system of compositive and optical front

The clear advantage of compositive solution:

● Offerred system designs simplify.

● Synchronous fluorescence detects the challenge that arouses with LED was eliminated, because this is,handle by optical front interior.

● Compositive and optical front still offerred more compact solution, electronic component is fewer.

● Reduced BOM and the complexity that supply government, realized smaller terminal unit at the same time.

The most crucial is, can adjust a key to configure parameter through firmware

Like photoelectricity diode driver of PD, LED and optical filter lens are configured. Below the circumstance of new without development hardware, disperse solution cannot come true but process designing sex. Should try the elapse as time, adjust platform in order to use new or when modification analytic method, of this kind of type can configuring a gender is crucial. Often be added in checking menu as a result of the new variation individual plant of pathogen and new disease, found to be able to revise the platform that analyses a method newly with suiting, and do not need to revise hardware, it is very advantageous.

Compositive and optical front has clear advantage, however, the function that glimmerings optical front decides in light application in weak light is not a negligible task. The letter a confusion of voices between more compositive and optical front is compared (the real property that SNR) number can not know optical receiver truly. As a result of luminous flux normally inferior, because this absolutely background noise of optical front is crucial parameter, is not to believe comparing of a confusion of voices. Although 1/f noise heft is met,limitation all is worth a method to be opposite the improvement of background noise degree, but we or the markers that can be based on fluorescence to measure are used all be worth a method to reduce background noise. Accordingly, noise of absolutely dark current, twinkle especially noise, it is dominant element. The dark current noise of the whole system that includes PD inside does not have a description in the data table in a lot of compositive and optical front, must measure alone.

Front of ADI compositive optics

The compositive and optical front of ADI, if MAX86171 suits PoC fluorescence application very much. Of imitate signal catenary and digital controller compositive the solution becomes the individual IC that makes realize smooth receiver likelihood. MAX86171 includes signal to recuperate photoelectricity diode to input, 19 charge are compositive ADC, driver of low noise LED and FIFO amortize are serial interface.

Graph 5. The block diagram of MAX86171 (come from at ADI)

● AFE has 9 LED passageway and 4 PD channel

● Enough passageway supports a variety of detecting the method supports what did not come to detect expand and need not undertake hardware upgrade.

● Can undertake process designing through SPI or I2C

● Allow to divide time to be being accumulated for example, all be worth the parameter such as limits and dynamic limits to undertake fine tuning

● FIFO support undertakes metrical below the dormancy mode of MCU, prolong the battery life of hand-held PoC system thereby.

More important is, this parts of an apparatus is had high-powered the character with low noise, can aid force compose to build the testing system of tall sensitivity. Have the aid of all is worth the character of function and low 1/f noise, the dark current noise of the signal chain that the area makes for the photoelectricity diode of 7.5 Mm2 is 11 PA Rms only, can detect reliably 1 PA comes the electric current of low photoelectricity diode inside 10 PA limits, apply to the fluorescence application of low luminosity especially. In addition, the PSRR with this outstanding parts of an apparatus and ambient light restrain character to be able to reduce systematic engineer to design the burden of power source and mechanical crust.

Graph 6. The weak smooth detector that undertakes with MAX86171 is measured

We use MAX86171 drive LED to pass multilayer and neuter density (ND) optics filter is received via photoelectricity diode again with function of test and verify. Through increasing the density of ND filter, optical attenuation can come in 40 DB (ND2) change between 140 DB (ND7) , from this imitate PCR or LAMP detect behavior of reductive of content of the fluorescence in the process. When attenuation under 140 DB when, MAX86171 can detect reliably the photoelectricity diode electric current of dark current of prep above background, and resolution is good at 10 PA. MAX86171 has so tall sensitivity, because photoelectricity diode join comes,be the dark current noise when optical front is very low, it is 11 PA Rms only.

Graph 7. The function result of MAX86171 (originate ADI)

Level of this one performance exceeded the typical requirement of PoC system, sufficient comfortable match what all sorts of biochemistry targets analyse content to detect.

Summary

Diagnose outside the body of rapid development (in IVD) system market, the optical sensor with right choice is particularly important. Compositive and optical front can simplify systematic design, reduced BOM and the complexity that supply government, realized smaller terminal unit at the same time.

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