The ECG signal is a bioelectrical signal generated by myocardial contraction and provides information on changes in cardiac physiological function. The measurement electrode is placed in different parts of the body, and the potential difference of different body surfaces is recorded, and the electrocardiogram is obtained. (ElectroCardioGram, ECG). Because it is easy to detect and has good intuitiveness, it is widely used in clinical medicine. However, the traditional ECG signal acquisition device is large in size and is not convenient for obtaining ECG signals in real time. Therefore, it is important to study portable, low-power ECG signal acquisition systems. Based on the low-power analog front-end ADS1293, this paper combines the MSP430 series low-power single-chip microcomputer to design an ECG signal acquisition system that can be used for ultra-low power consumption and miniaturization. 1 system hardware design The ECG signal acquisition system is mainly composed of the signal acquisition front end ADS1293 and MSP430 MCU control circuit. The working principle is as follows: the human body ECG signal extracted by the electrode is first sent to the ADS1293 for proper amplification and then analog-to-digital conversion to become a digital signal. Then, it is sent to the MSP430 MCU through the SPI interface for analysis and processing, and finally sent to the portable display device to display the waveform in real time through the USB interface of the MCU. Figure 1 system overall design block diagram 1.1 signal acquisition front end ADS1293 The ADS1293 is a 3-channel, 24-bit integrated analog front end for biopotential measurement from Texas Instruments. It can be set for each channel for a specific sample rate and bandwidth, enabling users to target performance and power consumption. Optimization. It also features AC/DC disconnection detection (Lead_offDetect), battery power monitoring and self-diagnosis alarms. It has a built-in right leg drive circuit for ECG applications to rent a Wilson/Goldberger terminal. The internal structure of the ADS1293 is connected to external pins as shown in Figure 2. The flow direction of the signal can be divided into signal input interface, signal processing unit and signal output interface. Figure 2ADS1293 schematic (1) Signal input interface. There are 6 signal input pins from IN1 to IN6. All input pins contain an electromagnetic interference (EMI) filter to filter out RF noise. The system uses a 5-lead connection, ie the right arm (RA), left arm (LA) and left leg (LL) are connected to the IN1, IN2 and IN3 pins respectively; the common mode detector (CMdetect) takes RA, LA and LL The average voltage is used as the input to the right leg drive (RLD) amplifier, and the output of the right leg drive amplifier is returned to the right leg (RL) terminal, which is input together from the IN4 pin. The function of the right leg drive circuit is to control the patient's common mode level and increase the AC rejection ratio of the system; the output of the Wilson Network (WCT) is connected to the IN6 pin and is used as the CH3 channel together with V1 (thoracic electrode) connected to the IN5 pin. Differential signal input. (2) Signal processing unit. It is mainly composed of three parts: instrument amplifier (INA), ∑Δ regulator (SDM) and low-pass digital filter (DigitalFilter). Its main function is to convert differential analog voltage signals into digital signals. The instrumentation amplifier is an operational amplifier circuit with high input impedance. It has two main functions: 1) Amplifying the differential signal. 2) Provide high input impedance to obtain a larger input signal from the ECG electrode. The output signal of the instrument amplifier is sent to the ∑Δ modulator for analog-to-digital conversion. The ∑Δ modulator is a one-bit coding technique based on oversampling, and the output reflects one bit of the encoded data stream of the input signal amplitude. The low-pass digital filter consists of three programmable 5th-order sin-type filters. The output of the ∑Δ modulator is processed by a low-pass digital filter to obtain an N-bit coded output. ZHANGJIAGANG DINSHENGLIN TRADING CO.,LTD , https://www.dslhouse.com
