Ultra-low power intelligent mobile ECG monitoring equipment

Abstract: Mobile intelligent sensing is a key technology for health monitoring and management. For the intelligent ECG sensor technology, three low-power modules for sensing, signal processing and communication are designed, and the system design is coordinated to reduce power consumption. A micro-load and long-term monitoring SMD ECG has been developed. Monitoring equipment with real-time ECG processing and heart rate detection. The smart sensing device has a volume of 24 mm × 16 mm × 10 mm and a mass of 1.73 g. Powered by a lithium polymer battery with an 80 mAh capacity, it can last for more than 7 days at a sampling rate of 256 Hz. After the data is wirelessly uploaded to the computer, the PC software can perform real-time display and processing of the electrocardiogram (ECG). In addition, the device can also transmit heart rate data to the mobile phone via Bluetooth for more than 14 days.

0 Preface

With the advent of an aging society, family personal monitoring and community medical care are booming. The demand for mobile low-power medical monitoring equipment is increasing. The central power long-term monitoring equipment evaluates health status and sudden heart. Early warning of vascular disease is of great significance. At present, the development of medical ECG monitors is relatively mature. Such devices often communicate with personal computers or industrial computers through wired transmission mode, and are widely used in hospitals for bed rest monitoring, and are not suitable for health or activity monitoring.

Mobile technology-based health monitoring is currently in the field of rapid development, and its core is low-power, miniature smart sensor technology to achieve long-term, micro-load monitoring. One type of product is a small Holter system, which stores the collected data to the memory, and the data needs to be manually exported to the computer for analysis, which sacrifices the real-time performance of the data and the power consumption of the storage operation is large. The current development trend is to combine smart sensors with wireless transmission technology, transmit the collected data to a computer or smart phone in real time, analyze the data through the client software, and further transmit the data to the server terminal of the health department such as a hospital. To build a complete healthy cloud system. How to reduce the system power consumption as much as possible to solve the contradiction between micro load and long-term monitoring is a key problem to be solved in developing health monitoring equipment.

In order to meet the needs of signal acquisition for portability, miniaturization, long-term monitoring and electro-cardiogram (ECG) analysis, this paper designs three low-power modules for sensing, processing and communication according to the low-power design principle. It also coordinates the overall system design to further reduce power consumption, and develops a patch-type ECG monitoring device with analytical functions and continuous operation.

1 system hardware design

1. 1 overall hardware design

According to the ECG signal characteristics and the requirements of the basic parameters of the acquisition system, a micro-load ECG monitoring system for the active human body was designed. The system hardware consists of the acquisition transmitter circuit and the receiver circuit. The acquisition transmitter circuit consists of a power module, a sensor module, a signal processing and a wireless communication module. The receiver circuit is composed of a wireless communication module and a UART communication module and is composed of a USB device. Port power supply. The overall hardware architecture of the system is shown in Figure 1.

Figure 1 system overall hardware framework

Fig 1 Frame of system overall hardware

1. 2 transmitter circuit design

The system uses a single-supply operation, front-mounted instrumentation amplifiers and operational amplifiers are powered directly from a lithium-polymerized battery. The nRF51822 is powered by ADP162, an ultra-low quiescent current CMOS linear regulator from Analog Devices. The analog front-end reference voltage is low-drift and low-power from TI. The power consumption reference REF3312 is provided.

The ECG signal is weak, easy to mix EMG signals and common mode power frequency noise, and there is a baseline drift phenomenon. In order to better improve the resolution of the ECG signal, a differential input method is adopted, and the ECG signal is amplified, filtered, and de-drifted. For the high internal resistance of the ECG signal, the front input has a high input impedance to reduce the interference caused by the bias current. As shown in Figure 2, the analog front end (AFE) consists of four parts: preamplifier, secondary amplification, notch filter, and low-pass filter. The reference voltage of the analog front end is set to 1.2 V for the single-supply operation and the sampling characteristics of the ADC.

Figure 2 Analog Front End Schematic

Fig 2 Principle diagram of AFE