CN101884529B - Electronic sphygmomanometer and calibration method thereof - Google Patents

Abstract

An electronic sphygmomanometer, including a pressure sensor, a display screen and a signal processing circuit. The pressure sensor converts the pressure signal in the cuff into an electrical signal, and displays systolic blood pressure, diastolic blood pressure and average blood pressure on the display screen after being processed by the signal processing circuit. The signal processing circuit includes a programmable gain amplifier, a band-pass filter, an analog-to-digital converter and an MCU, and the programmable gain amplifier, a band-pass filter, an analog-to-digital converter, an MCU and a driver circuit of the display screen are integrated in an SoC chip. The electronic sphygmomanometer of the invention has the advantages of simple peripheral circuit, low cost and good stability. The present invention also relates to a method for calibrating an electronic sphygmomanometer, which is realized through parameter setting in the SoC and can be automatically completed by program control, which greatly simplifies the calibration process, and the calibrated product will not be affected by vibration during transportation and has good stability .

Description

Electronic sphygmomanometer and its calibration method

technical field

The invention relates to a sphygmomanometer, especially an electronic sphygmomanometer and an automatic calibration method thereof.

Background technique

The vast majority of non-invasive electronic sphygmomanometers and blood pressure monitors use the oscillometric method, and the oscillometric blood pressure measurement control hardware (PCBA) mainly includes pressure sensors, constant current sources, amplifiers and filters, buttons, pump\valve drives, displays, etc. parts. Taking the step-down test method as an example, during the deflation process, the pressure sensor converts the pressure signal in the cuff into an electrical signal, and the electrical signal passes through a filter to obtain a pulse pressure wave with a parabolic envelope, and finally the systolic blood pressure (SBP) is calculated by the blood pressure algorithm. ), diastolic blood pressure (DBP) and mean blood pressure (MAP).

At present, electronic sphygmomanometers are realized by combination of separate components, the circuit is complicated and the cost is high. They are debugged and calibrated by the potentiometer, which is cumbersome to operate, and the potentiometer is easily changed by vibration during transportation, and the stability is poor.

Contents of the invention

The object of the present invention is to provide an electronic sphygmomanometer with simple peripheral circuit, low cost and good stability and its calibration method.

The electronic sphygmomanometer of the present invention includes a pressure sensor, a display screen and a signal processing circuit. The pressure sensor converts the pressure signal in the cuff into an electrical signal, and displays systolic blood pressure, diastolic blood pressure and average blood pressure on the display screen after being processed by the signal processing circuit. It is characterized in that the signal processing circuit includes a programmable gain amplifier for amplifying the output signal of the pressure sensor in proportion to match the input range of the analog-to-digital converter, and is used for extracting the pulse signal from the output of the programmable gain amplifier The band-pass filter, the analog-to-digital converter used to convert the analog signal output by the band-pass filter and the programmable gain amplifier into a digital signal, and calculate the systolic blood pressure, diastolic blood pressure and average blood pressure based on the signal output by the analog-to-digital converter MCU, the programmable gain amplifier, band-pass filter, analog-to-digital converter, MCU and the driver circuit of the display screen are integrated in a SoC (System on a Chip) chip.

Furthermore, a digital filter program can be built in the MCU to filter out the influence of 50Hz power frequency interference on the pulse signal.

Further, a real-time clock module that provides clock signals for the MCU and the analog-to-digital converter can be integrated in the SoC chip.

The present invention also provides a method for calibrating an electronic sphygmomanometer, which can be automatically implemented through a program, and specifically includes the following steps:

a. Set an empirical gain parameter and bias parameter for the programmable gain amplifier;

b. Make the force on the pressure sensor be 0, the MCU changes the bias parameters of the programmable gain amplifier and detects whether the output of the analog-to-digital converter is within the appropriate range of zero-point internal code values, and performs zero-point pre-calibration, so that the programmable gain amplifier can get accurate bias parameters;

c. Make the force on the pressure sensor be the maximum value of the sphygmomanometer range, the MCU changes the gain parameter of the programmable gain amplifier and detects whether the output of the analog-to-digital converter is within the appropriate range of full-scale point internal code values, and performs full-scale point Calibration, so that the programmable gain amplifier can obtain accurate gain parameters;

d. Make the force on the sensor be 0, and the MCU collects and stores the internal code value of the analog-to-digital converter at this time, and completes the zero point calibration; and

e. Make the force on the sensor be the specified value, and the MCU collects and stores the internal code value corresponding to the analog-to-digital converter, and completes the middle point calibration.

The present invention integrates a programmable gain amplifier (PGA), a filter, an analog-to-digital converter (ADC), an MCU, an LCD drive circuit, etc. in one SoC chip, and the entire electronic sphygmomanometer circuit only consists of one SoC chip, a pressure sensor and a small amount of Composed of external resistance-capacitance components, the peripheral circuit is greatly reduced, and hardware expenditure is reduced, thereby greatly improving production efficiency and reducing production costs.

It has built-in programmable gain and offset parameter settings inside the SoC, and makes personalized settings for the range and offset of each pressure sensor, maximizing the range of the ADC and greatly improving the efficiency of the ADC. The waste of ADC is avoided, and the purpose of reducing production cost is further achieved.

Its system calibration and debugging are realized through the parameter setting in the SoC, which can be automatically completed by program control, which greatly simplifies the calibration process, and the calibrated product will not be affected by the vibration during transportation, and has good stability.

Description of drawings

Fig. 1 is the schematic diagram of this electronic sphygmomanometer;

Fig. 2 is a schematic diagram of the programmable gain amplifier in Fig. 1;

Fig. 3 is a schematic diagram of the bandpass filter in Fig. 1;

Figure 4a is a waveform diagram of the pressure signal output by the PGA measured in the experiment;

Figure 4b is a waveform diagram of the pulse signal output by the bandpass filter measured in the experiment;

Figure 5a-c is a schematic diagram of the system calibration process, where a shows zero point pre-calibration, b shows full-scale point calibration, and c shows zero point and intermediate point calibration.

Detailed ways

Referring to Fig. 1, the electronic sphygmomanometer includes a pressure sensor 2, a display screen 3 and a signal processing circuit 1. The pressure sensor 2 converts the pressure signal in the cuff into an electrical signal, and displays the contraction on the display screen 3 after being processed by the signal processing circuit 1. pressure, diastolic pressure and average blood pressure, the signal processing circuit 1 includes a programmable gain amplifier (PGA) 11 for amplifying the output signal of the pressure sensor 2 in proportion to match the input range of the analog-to-digital converter 13, A band-pass filter 12 for extracting the pulse signal from the output of the programmable gain amplifier 11, an analog-to-digital converter (ADC) for converting the analog signal output by the band-pass filter 12 and the programmable gain amplifier 11 into a digital signal 13, and the MCU 14 for calculating systolic blood pressure, diastolic blood pressure and average blood pressure according to the signal output by the analog-to-digital converter, the programmable gain amplifier 11, the band-pass filter 12, the analog-to-digital converter 13, the MCU 14 and the display The driving circuit 15 of the screen 3 is integrated in an SoC chip.

PWM0 in Fig. 1 is the driving signal of the pressure pump, which is used to control the pressure pump to inflate the cuff. PWM1 is the driving signal of the exhaust valve, which is used to drive the exhaust valve to work and control the discharge of gas in the cuff.

The pressure sensor 2 adopts a resistive pressure sensor, which consists of four equal-value resistors to form a bridge, and its output voltage is proportional to the input pressure, such as: Home Base MPS-3110 and UMC US-09111-006. The pressure sensor 2 is driven by a constant current source. The constant current source is composed of an operational amplifier OP1 and two resistors to provide a constant current for the pressure sensor 2. The operational amplifier OP1 constituting the constant current source is integrated in the SoC chip. The pressure sensor 2 can also be driven by a constant pressure source.

The programmable gain amplifier 11 adopts a programmable instrument amplifier. The main feature of the instrument amplifier is that it has high input impedance and does not affect the constant current circuit of the sensor, and at the same time, it can ensure high gain for small signal amplification. Referring to FIG. 2 , the programmable instrument amplifier 11 includes two parts of programmable gain, and the gain multiplier can be set in multiple levels respectively. If necessary, the output range can be adjusted through two bias voltages V _REF1 and V _REF2 respectively. Referring to Figures 1 and 2, one output of the programmable instrument amplifier 11 is to the input channel AN1 of the ADC13, which is output to the bandpass filter 12 at the same time, and the other output of the programmable instrument amplifier 11 is to the input channel AN0 of the ADC13.

Referring to Figures 1 and 3, the bandpass filter 12 is composed of two operational amplifiers OP2, OP3, peripheral resistors R1-R12, and capacitors C1-C5, and its bandwidth is 10Hz-500Hz. The input terminal of the band-pass filter 12 is connected to an output terminal of the programmable gain amplifier 11 , and the output terminal of the band-pass filter 12 is connected to the input channel AN2 of the analog-to-digital converter 13 . The pressure signal output by the programmable gain amplifier 11 is filtered by the band-pass filter 12 to obtain the pulse signal. Thus, two signals needed for oscillometric blood pressure measurement are obtained: pressure signal and pulse signal. Shown in Fig. 4a is the waveform of the pressure signal output by the programmable gain amplifier 11 measured in the experiment, shown in Fig. 4b is the waveform of the pulse signal after the pressure signal of Fig. 4a is filtered by the band-pass filter 12, and the acquisition process of the signal is Take the detection of pressure and pulse signals as an example when the cuff is deflated.

For 50Hz power frequency interference, the front end has been processed by low-pass filtering on the hardware circuit. If it is not completely suppressed, it will affect the system’s confirmation of the pulse peak value in the application. Therefore, in the present invention, a digital filtering program is built in MCU14. The algorithm is used to filter out the influence of 50Hz power frequency interference on the pulse signal, so as to improve the measurement accuracy of the sphygmomanometer.

The SoC chip has a built-in real-time clock (RTC) module that provides clock signals for the MCU and the analog-to-digital converter. In addition, this electronic sphygmomanometer has a power-saving mode, and the SoC has a built-in wake-up circuit, which can be used to turn off the DC/DC device in the power-saving mode.

Due to the inherent characteristics of semiconductor materials, pressure sensors generally have the following problems: I. Consistency problem: Even the sensors produced in the same batch will have relatively large discreteness in their characteristics. In order to ensure sufficient accuracy, each The sensor is calibrated. II. Temperature drift problem: Semiconductor materials are very sensitive to temperature changes. In the actual test of 1mmHg/10°C, certain measures must be taken to compensate for the temperature drift of the sensor. III. Time drift problem: In the actual test, semiconductor materials sometimes drift, and there is 3mmHg per minute. Generally speaking, the test process will not exceed 40 seconds. The electronic sphygmomanometer of the present invention adopts the zero-returning mode when starting up (the pressure sensor must first perform zero offset correction when starting up), which can effectively solve the problem of drifting.

For the discrete problem of the sensor, the electronic sphygmomanometer of the present invention realizes the calibration of the sensor by adjusting the gain parameter and the bias parameter of the built-in programmable gain amplifier during the system calibration process. The calibration of the sphygmomanometer can be automatically realized through the program. Referring to Figure 5a-c, the specific calibration method includes the following steps in sequence:

a. Set an empirical gain parameter and bias parameter for the programmable gain amplifier;

b. Make the force on the pressure sensor be 0, the MCU changes the bias parameters of the programmable gain amplifier and detects whether the output of the analog-to-digital converter is within the appropriate range of zero-point internal code values, and performs zero-point pre-calibration, so that the programmable gain amplifier can get accurate bias parameters;

c. Make the force on the pressure sensor be the maximum value of the sphygmomanometer range, the MCU changes the gain parameter of the programmable gain amplifier and detects whether the output of the analog-to-digital converter is within the appropriate internal code value range of the full-scale point, and performs full-scale point calibration , so that the programmable gain amplifier can obtain accurate gain parameters;

d. Make the force on the sensor be 0, and the MCU collects and stores the internal code value of the analog-to-digital converter at this time, and completes the zero point calibration; and

e. Make the force on the sensor be the specified value, and the MCU collects and stores the internal code value corresponding to the analog-to-digital converter, and completes the middle point calibration.

In the above step b, the internal code value of the zero point is 2 ⁿ x 1/8, where n is the number of digits of the analog-to-digital converter, and when the output of the analog-to-digital converter is close to 2 ⁿ x 1/8, the bias at this time The parameters are specified as the exact bias parameters of the programmable gain amplifier.

In the above step c, the internal code value of the full-scale point is 2 ⁿ x7/8, where n is the number of digits of the analog-to-digital converter, and when the output of the analog-to-digital converter is close to 2 ⁿ x7/8, the current The gain parameter is defined as the exact gain parameter of the programmable gain amplifier.

The calibration refers to recording the ADC internal code value corresponding to the fixed point pressure of the pressure sensor. The purpose of the calibration is to enable the MCU to calculate the actual pressure through the obtained internal code value during the measurement process. The selection of specific calibration points depends on the linear characteristics of the pressure sensor.

Claims (4)

1. An electronic sphygmomanometer, including a pressure sensor, a display screen and a signal processing circuit. The pressure sensor converts the pressure signal in the cuff into an electrical signal, and displays systolic pressure, diastolic pressure and average pressure on the display screen after being processed by the signal processing circuit. blood pressure, characterized in that: the signal processing circuit includes a programmable gain amplifier for proportionally amplifying the output signal of the pressure sensor to match the input range of the analog-to-digital converter; A band-pass filter for extracting the pulse signal, an analog-to-digital converter for converting the analog signal output by the band-pass filter and a programmable gain amplifier into a digital signal, and calculating systolic and diastolic blood pressure based on the signal output by the analog-to-digital converter and the MCU of the average blood pressure, the driver circuit of the programmable gain amplifier, band-pass filter, analog-to-digital converter, MCU and the display screen is integrated in an SoC chip; the band-pass filter is composed of two operational amplifiers It is composed of external resistors and capacitors, and its bandwidth is 10Hz-500Hz. The input terminal of the bandpass filter is connected to the second output terminal of the programmable gain amplifier, and the output terminal of the bandpass filter is connected to the input channel AN2 of the analog-to-digital converter. ; The second output terminal of the programmable gain amplifier is connected to the input channel AN1 of the analog-to-digital converter, and the first output terminal of the programmable gain amplifier is connected to the input channel AN0 of the analog-to-digital converter. 2. The electronic sphygmomanometer according to claim 1, wherein the pressure sensor is driven by a constant current source, the constant current source is composed of an operational amplifier and a resistor, and the operational amplifier constituting the constant current source is integrated in the SoC chip. 3. The electronic sphygmomanometer according to claim 1, characterized in that: said MCU has a built-in digital filter program to filter out the influence of 50Hz power frequency interference on the pulse signal. 4. The electronic sphygmomanometer according to claim 1, characterized in that: a real-time clock module that provides clock signals for the MCU and the analog-to-digital converter is integrated in the SoC chip.

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