Portable medical electronics has seen considerable growth in recent years and has been widely adopted by the industry. Many new companies in the market continue to introduce new derivatives. What is needed is a better mass production design that provides lower complexity and acceptable performance levels, allowing the operator to lower the cost of the device. Some important factors to consider when designing a medical device include selecting the right part to meet specifications, power consumption, cost, size, etc., and passing the US Food and Drug Administration (FDA) inspection.
A typical portable medical electronic system with built-in components including analog front-end components for extracting data, amplifiers and filters for signal conditioning, analog-to-digital converters, buttons for collecting user feedback, and micro-calculations Controller and various interfaces for connecting the LCD screen to the USB port. The traditional design approach is to place all the required components on the board, but this approach increases the overall bill of materials, PCB complexity, and design cycle. These analog components reduce the immunity of the analog IP because the solution can be easily reverse engineered. The design and manufacture of portable medical electronic products is regulated by the US Food and Drug Administration (FDA), which means that the design and manufacture of products must accurately follow the procedures specified in the text, and their performance must meet strict records, development tests, product testing. And on-site maintenance and other regulations. One of the FDA's provisions stipulates that the parts used in portable medical electronics must not be interrupted in the next five years. It is therefore easier for R&D operators to reduce the number of BOM parts to pass the FDA inspection. Some portable medical electronic devices commonly used in home care and clinics, including sphygmomanometers, contactless digital thermometers, blood glucose meters, and pulse oximeters. Figures 1 and 2 show a typical sphygmomanometer and a contactless digital thermometer manufactured using conventional methods.
Traditional method
A typical sphygmomanometer uses a differential pressure sensor to measure the blood pressure of a wrist or arm. The sensor's output signal is only a few microvolts (30μV to 50μV). The output blood pressure signal must be amplified with a high gain instrumentation amplifier with an ideal CMRR (common mode rejection ratio). The ideal gain and CMRR are typically 150dB and 100 dB, respectively. The oscillation pulse frequency of the blood pressure signal is between 0.1 Hz and 11 Hz with an amplitude of several hundred microvolts. These signal oscillations can be extracted using a bandpass filter with a gain of approximately 200 and a cutoff frequency of 0.3 Hz to 11 Hz. A 10-bit analog-to-digital converter with a speed of 50 Hz can be used to digitize the signals from the blood pressure sensor and oscillator. The product uses two timers to calculate the heartbeat and the safety timer function. The safety timer keeps the subject's blood pressure stable for a period of time, following the guidelines of the American Association for the Advancement of Medical Devices (AAMI). The microcontroller core uses an oscillating algorithm to calculate the values ​​of systolic and diastolic blood pressure. The sphygmomanometer wristband uses a pulse-modulating component to drive the motor for inflation and deflation.
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