The Design Of The Heart-electricity Signals Collecting And Processing Circuit

Electrocardiogram monitor is a precise electronic-medical equipment inmodern medical research and clinic diagnosis. The electrocardiogrammonitoring system mainly consisted of the function of collecting, analyzingand diagnosing heart-electricity signals is widely used, which records thesignals of heart-electricity impulse to check out the condition of a patient'sheart, to prevent or diagnosis heart attack. It is of great use and meaning inprotecting people's physical health and improving people's life quality.The very circuit in charge of collecting and processing heart-electricitysignals is the main part of a electrocardiogram monitor, which is a monitoringcircuit that processes both analog and digital signals. The former of thatmonitoring circuit is a heart-electricity collecting system based on analogtechnique, behind of which is a wave-showing circuit totally based on digitalsignal processing. The structure of this monitoring circuit is clear and easy toaccomplish.Then, we are going to discuss designing the heart-electricity signalscollecting and processing circuit.In the former part about theory concerns, we introduce the definition andcharacter of bioelectricity signals, the restrict of bioelectricity signal detecting,the principle of heart-electricity signals producing and the character ofheart-electricity signals, so that we could get full awareness of the differencesbetween heart-electricity signals and other electricity signals, and get a basicpreparation for future design. The character of a biology system is the highstructurally complexity, constant transform and self-adaptability. Strictly, allbiomedicine signals are stochastic, so it is difficult to process and analysisbiomedicine signals. As for heart-electricity signals, it is periodical butincertitude, it varies along with all kinds of physiology elements.On circuit designing, we emphasis collecting and processing the analogheart electricity signals. Considering the character of heart-electricity signalsand the special electric demand in biomedicine, the signal collecting andprocessing circuit is mainly consisted of the following part: buffer, conductioncontrol, optional circuit, weak signal difference amplifier, signal filter,opti-electric isolation, industry frequency(50Hz) filter circuit and a specialfunction circuit which increases CMRR., such as right leg driver and shielddriver. Else, in the part of digital signal processing circuit, we introduce themicro-controller, A/D, software design loop.Heart electricity signals is weak bioelectricity signals with high sourceimpedance, it is a "mv level" and "low frequency "signal. To measure heartelectricity signals precisely, the kernel concerns in designing are highperformance signal fore-processing circuit. Buffer stage for impedanceswitching, which transform high impedance heart electricity signals into lowimpedance signals. The main electric demands of a signal amplifier are highgain, high impedance, high CMRR, also, low maladjustment voltage and biascurrent is must to keep the signal steady. The amplification ratio of the signalsdepends on the proportion OP circuit. To achieve a high CMRR, a meteramplifier is a good choice, the gain coefficient could be adjusted. Acombination of separate OPs is accepted.Heart electricity signals are so special that a pure electric signal of oneposition can not be detected without interferences. What we get always arecombinations of signals from 9 positions. In order to record the activities of aheart, A multi-conduction HES(heart electricity signals) detecting mode, Thereare 12 conduction mode, we are going to discuss the principle and all theconduction mode in detail in the main text.Heart-electricity signals is a set of low frequency signals surrounded by alot of more powerful interferences and noises(muscle-electricity, industryinterference, amplifier noise, noise generated at the interface between the poleand skin, etc. ), The lowest frequency of this set of signals is below 1Hz. In thecircuit design, filtering especially against industry frequency interference ismost important. How to match the resistors and capacitors perfectly is the verykey in filtering design. Software filtering and hardware filtering are to meansavailable. The advantage of the former is that the circuit structure can be verysimple, and the excursion of the stop frequency is mini, filter point is precise.But the noises in former part will influence the circuits follows, and thewaveform we got will distort. So we employ hardware filtering. It is proventhat a hardware filtering design performs very well.At the same time we collecting heart-electricity signals, our patient'ssafety must be under fully consideration. To prevent electric shock, signalisolating measures must be taken. Amplifier isolation and opti-electricisolation techniques are often used. Opti-electric couplers, digital couplers,difference bus equipments and multi-function data collecting ICs are used inthis design. There are different system designs depending on the character ofpower supply and the signals. In this signal processing circuit, we mainlyadapt opti-electric couplers, which provide us both high performance and lowcost.In digital signal processing, the main concern is how to show the exactwaveform, calculating and analyzing is not needed, and a clear and simplesoftware design can achieve real-time showing,This heart-electricity signals collecting and processing module circuit isdesigned to monitor a serious ill-patient's heart activities for 24 hours. Thedesign should meet following requirement: (1)simple structure, low cost;(2)multi-pole and reference-pole, multi-conduction available;(3)high gain,high CMRR, high performance in filtering;(4)real-time displaying, easy toobserve and analysis;(5)easy to use, switch different conduction mode bypressing certain buttons.Please refer to the main body for detail information.