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Medical-grade 12-lead ECG solution based on Lixin LH001-91

Cardiovascular disease is a serious threat to human life and health. With the acceleration of the aging process of the population and the increase of social pressure and other factors, the prevalence rate is showing an upward trend year by year, and it is getting younger and younger.
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Medical-grade 12-lead ECG solution based on Lixin LH001-91

1. Introduction to LH001-91

1.1. Structure diagram

Figure 1. LH001-91 Structure Diagram

 

1.2. Features

  • Low Noise Programmable Gain Amplifier (PGA) and High Resolution 24-Bit Analog-to-Digital Converter (ADC)< /section>
 
— Programmable gain: 1/2/4/6/8/12/24/48
— 4 differential inputs
— Integral nonlinearity: 2 PPM/FS
 
  • Electrocardiogram (ECG)
— Input referred noise: 2.9 μVpp (250 SPS, gain 6)
— ECG channel input bias current: 200pA
— data rate: 125SPS to 8kSPS
— Common Mode Rejection Ratio (CMRR): 117dB
— built-in right leg drive amplifier, continuous line break detection, test signal
  • Built-in oscillator and reference voltage
  • Standby Mode
— current 0.1 μA
 
  • Power
— Analog: 2.4V to 3.6V
— digital: 1.7V to 3.6V
  • Built-in integrated excitation current source
  • 4-wire SPI interface
  • Operating temperature range: -40°C ~ +85°C
  • 40 pins, 5mm x5mm QFN package
  • 30 pins, 2.95mm x2.95mm WLCSP package
 
 

2. Measurement principle

The reason why blood can circulate continuously in the human body is because the human heart continues to excite and contract regularly. The excitation of the sinoatrial node causes the heart to beat. The excitation here refers to the result of the joint action of depolarization and repolarization of cardiomyocyte electrical activities. The figure shows the schematic diagram of the depolarization and repolarization process of cardiomyocytes. Cardiomyocytes are stimulated to cause positive charges outside the cell membrane to flow into the cell, making the inside of the cell membrane a positive potential and the outside of the cell membrane a negative potential. This process is called the depolarization process. Due to cell metabolism, the state of charge inside and outside the cell is slowly restored to the polarized state. This restoration process is called the repolarization process. Excitement is transmitted from the sinoatrial node to the atrium and ventricle in turn, so that the potential difference of the entire heart area is exposed to a continuously changing state, thereby generating a regularly changing current.

Figure 2. Schematic diagram of myocardial depolarization and repolarization

 

This initial ECG signal spreads throughout the human body under the conduction of body fluids, so the human body surface will generate periodically changing electric potentials. Place two electrodes at appropriate positions on the surface of the human skin to obtain corresponding potentials, and the measured potential difference between the two positions is a regularly changing periodic signal. On the surface of the human skin, these regularly changing ECG signals are obtained by the ECG acquisition device and drawn as a graph, which is our common ECG.

3. Program introduction

Figure 3. Scheme block diagram

 

The program block diagram introduces the realization of 12 LEAD ECG signal detection based on LH001-91, and 10 electrodes are connected to 8 LH001-91 conversion channels to generate 12 ECG signals. The 10 electrode locations are LA left arm, LL left leg, RA right arm, RL right leg, and V1-6 chest.  Use the LH001-91 integrated RLD op amp to generate a shared right leg drive signal to improve the common mode rejection capability of the system. Three low-noise discrete op amps implement the Wilson Termination (WCT) function.  

Figure 4. Electrode position map

 

12-lead signal, 8 of which are generated by LH001-91 conversion, the specific configuration method is as follows.

 

The other 4 lead signals are obtained indirectly through calculation according to the table below.

 

 

The picture below is the actual picture of the customer's demonstration board connected to the ECG simulator. Linghui Lixin can provide a full set of Demo board and host computer software.

 

Figure 5. Demo board physical picture

 

The demo board collects the ECG simulator signal under the condition of computer USB power supply, and draws the ECG as shown below, the signal does not pass through Any external filter processing, fully meet the medical needs.

 

Figure 6. 12-lead ECG waveform

 

4. Summary

The chip used in the above measurement scheme has its own internal reference voltage, the input noise is 2.9 μVpp (250 SPS, gain 6), the common mode rejection ratio ( CMRR) 117dB, integral non-linearity 2 PPM/FS, 24-bit high-precision ADC, support lead continuous disconnection detection, low-temperature drift programmable gain amplifier medical grade domestic ECG AFE products, sufficient supply and reasonable price, which is also It is the advantage of domestic chips.