The definition of SoC is diverse, and it is difficult to give an accurate definition because of its rich content and wide application range. In a narrow sense, it is the core chip integration of the information system, which integrates the key components of the system on a single chip; in a broad sense, the SoC is a micro-small system. If the central processing unit (CPU) is the brain, then the SoC It is the system that includes the brain, heart, eyes, and hands. Academia at home and abroad generally tends to define SoCs as integrating microprocessors, analog IP cores, digital IP cores, and memory (or off-chip memory control interfaces) on a single chip. It is usually custom-made or for specific uses. Standard product.
The main process of oscillometric blood pressure detection is to obtain the pressure signal in the cuff, analyze the pulse signal separated from it, find the position corresponding to systolic blood pressure and diastolic blood pressure, and obtain the data. The traditional oscillometric method is to amplify the signal from the sensor, low-pass filter the amplified signal to obtain a pressure signal, and send it to the single-chip microcomputer by a group of A/D converters, and then perform the pressure signal. Bandpass filtering, which obtains the pulse signal, is sent to the microcontroller by another set of A/D converters. The basic structure is shown in Figure 1.
The A/D converter is used to convert analog quantities into digital quantities through a certain circuit. The analog quantity can be an electrical signal such as voltage or current, or a non-electrical signal such as pressure, temperature, humidity, displacement, and sound. However, before the A/D conversion, the input signal input to the A/D converter must be converted into a voltage signal by various sensors through various sensors. After A/D conversion, the output digital signal can have 8 bits, 10 bits, 12 bits, and 16 bits.
Thanks to the integration of a high-precision 16-bit Σ-Δ A/D converter, the A/D reference voltage can be programmed (minimum 10mV). Therefore, it can perform A/D conversion directly without guaranteeing accuracy and dynamic range requirements. In this way, a series of problems such as dynamic range change, noise, and voltage offset due to the presence of the amplifier can be eliminated, and the use of the device is reduced, and the implementation cost is reduced.
Since the Σ-Δ type A/D converter provides a differential mode input mode, the differential mode signal given by the sensor can be directly sent to the A/D converter, and the common mode rejection ratio can theoretically reach infinity. Therefore, it can greatly reduce the common mode interference caused by the mismatch of the preamplifier circuit.
Since the Σ-Δ A/D converter conversion process is filtered by a low-pass filter, it is not necessary to perform filtering before the A/D conversion, and the sensor can be directly connected to the A/D before the digital Filtering.
Since a standard constant current source is integrated in the ADμC848, the constant current value can be adjusted by software programming. Therefore, according to the different environments of the product application, a standard pressure output can be sampled, then A/D conversion, and then the constant current source can be adjusted according to the conversion result until the desired conversion value is output, so as to achieve automatic calibration of the product.
The improved electronic sphygmomanometer hardware structure is shown in Figure 2.
After the above hardware processing, the curve of the pressure in the cuff is obtained. In the software processing, the pulse signal is first separated; then the interference point is removed, the envelope curve is fitted, and the corresponding average pressure is found; finally, the coefficient is calculated according to the coefficient. Systolic and average pressure.
A morphological filtering algorithm is introduced in the process of separating the pulse signals. Since the pressure signal in the cuff is close to the pulse signal band, direct band-pass filtering reduces the signal amplitude and reduces the signal-to-noise ratio, which brings difficulties to the subsequent processing. The application of the morphological filtering algorithm is to separate the signal from the morphological point of view and extract the pulse signal well. In order to complete the signal separation in real time, the open operation is used to process all the peaks in the original signal, and then the original signal is compared with the processed signal to obtain the separated pulse signal. Figure 3 is the original signal diagram and Figure 4 is the separated pulse signal.
In order to effectively suppress the interference and repair the defective pulse wave, the reliability of each pulse wave is determined according to the relationship between the peak value of each pulse wave and the pulse wave peak adjacent thereto. Since the amplitude of the pulse wave is not monotonous, such a judgment also requires consideration of the amplitude factor. The specific method is described in the literature.
The envelope fitting is performed using the weight information of each pulse wave obtained above. Since the resulting envelope is clearly asymmetrical, a third-order least squares fit with weights will be used. After the fitting is completed, the pressure value corresponding to the position of the maximum value on the curve is the value of the average pressure.
Finally, according to the magnitude of the average pressure, which amplitude coefficient is used, and the amplitude coefficient is used to calculate the corresponding position of the systolic pressure and the diastolic pressure, thereby obtaining the systolic pressure and the diastolic pressure.
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