introduction
Health is closely related to everyone and has become a hot spot in today's human society. The wearable medical monitoring system can easily collect human health data, predict and diagnose diseases. The wearable medical chip system solution based on low-cost, low-power, high-transmission-rate wireless communication technology helps patients to collect basic life parameters of the body in real-time work and life, and reduces the face-to-face consultation time of doctors and patients. In order to shorten the waiting time of patients in the hospital, thereby alleviating the contradiction of the current shortage of medical resources, and also improving the quality of patients seeking medical care. In addition, chronic diseases (such as high blood pressure, diabetes, high blood lipids) have become the number one killer of human health today. The treatment of chronic diseases cannot be separated from the long-term and uninterrupted collection and monitoring of patients' physical health data. Wearable medical chips are easy to accept due to their small size, low power consumption and low cost of use. The huge potential consumer market prospects have attracted many chip design companies such as Philips (Zarlink, Ti, etc.) to join their R&D and commercial applications. Promotion.
With the development of integrated circuit technology and biomedical engineering technology, more and more wearable medical chips and micro-systems have been developed, which are widely used in human medical and health monitoring, such as blood oxygen sensors worn at the fingertips. , watch type blood glucose sensor, watch type sleep quality monitor, sleep physiology checker, belt type respiratory heart rate monitor, implantable identification component, and the like. The wireless wearable medical micro system consists of a number of wireless sensors placed on the body surface, such as clothes, watches, jewelry, etc. that people usually wear, can be used to insert micro-wearable medical chips. Due to the large number of wires connected between different sensors and between the main processing display chips, it is inevitable to cause great inconvenience to the user. The advantage of wireless communication technology as an alternative transmission method for wires is that the advantages are It is particularly prominent. At present, most wireless communication technologies are focused on increasing the transmission rate of wireless data, and wireless transmission technologies for wearable medical systems must also consider minimizing power consumption during wireless signal transmission. The transceiver part of the wearable medical chip for transmitting and receiving wireless signals is usually the most energy-consuming part of the entire medical chip. In order to facilitate the long-term wear and use of the customer, the power consumption of the wireless transmission part of the circuit is undoubtedly required by the wearable chip designer. Key issues to consider. Around the goal of low power consumption and high transmission rate, Zarlink, Nordic, Philips, chipcon and other companies have successively launched solutions for ultra-low power RF transceiver chips.
1 wearable medical system chip structure
The overall structure of the wearable medical chip based on the wireless communication technology is as shown in FIG. 1 , and generally consists of a physiological signal acquisition circuit, an analog-to-digital conversion circuit (ADC), a digital signal baseband processing circuit, a controller, and a transmitting and receiving circuit. Firstly, the physiological data of the human body is collected by the signal acquisition low-noise instrumentation amplifier circuit, and then the acquired physiological signal is converted into an easy-to-process digital signal by AD conversion, and processed by a digital circuit after encoding, FFT, etc., through the transmitting circuit. Go out. At the same time, external control signals and data can also be received by the receiving circuit on the chip. The controller is used to control the operation of the entire chip, and can be programmed to meet different application requirements. Typically, a high-performance wearable medical chip consists of high-performance digital, analog, and RF components, especially the performance of the analog and RF components, directly affecting the overall performance of the chip. The medical chip analog and RF transceiver parts are obviously the most power-consuming part of the whole chip. Therefore, when designing these two parts of the circuit, the designer usually has to balance the low power and high performance. Below, the various components of a typical wearable medical system chip are described.
Figure 1 Structure of the wearable medical chip system
Fig.1 Wearable medical SOC chip structure diagram
1.1 Physiological signal acquisition low noise amplifier
The acquisition of physiological signals is typically obtained by on-chip integrated biosensors. For ease of integration, the sensor is implemented in a low-noise amplifier in a CMOS process that converts biosignals into bioelectrical signals. In order to obtain a variety of physiological information at the same time, multiple amplifiers with different functions can be integrated on the chip to form multiple channels to collect blood pressure, blood oxygen saturation, respiratory rate, heart rate, body temperature and other physical parameters. Since the physiological signal of the human body is relatively weak and susceptible to noise from the surrounding environment, the amplifier needs high sensitivity, high gain, low noise, and low power consumption. At the same time, a low-pass filter with a cutoff frequency of about 1 kHz is used after the amplifier. To further filter out interference noise at frequencies other than bioelectrical signals. Amplifiers can be designed in a variety of operating modes, such as listening, working, and sleeping, to reduce chip power consumption.
1.2 AD converter (ADC)
The front multi-channel physiological signal acquisition amplifier collects a variety of physiological information and is connected to the input port of the ADC through an analog multiplexer. The analog multiplexer can only select one preamplifier output at a time. In order to reduce power consumption, the ADC usually selects a successive approximation structure with a bit number of about 10 bits. In order to improve the accuracy and conversion rate, you can also use sigma-delta or pipelined ADC. The higher the number of bits, the higher the conversion rate, but the higher the power consumption. The design of wearable medical chips, low power is the key. . In addition, the unit capacitance of the ADC should be selected. If the selection is too large, it will occupy a large area of ​​the chip. At the same time, it is also considered to minimize the influence of parasitic capacitance on the unit capacitance.
1.3 Controller
The chip can adopt ARM core and MCU as the controller to control the working mode of other parts of the chip through the bus; it can control the working timing of the data, configure the register, and control the real-time communication of the data bus by other parts of the chip.
1.4 Digital Signal Processing Baseband
In order to improve the data transmission rate and accuracy and security, the digital signal output by the ADC needs to be digitally compressed and encoded by the digital signal baseband processor, and the interference frequency noise can be further filtered by FFT conversion and digital filtering.
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