Zero-point voltage output bias control circuit of sensor

Abstract

The utility model discloses a zero-point voltage output bias control circuit of a sensor. The circuit comprises the sensor, the sensor is connected with a differential amplification circuit, the differential amplification circuit is connected with an ADC module, the ADC module is connected with a controller module, the controller module is connected with a DAC module, and the DAC module is connected with a bias voltage adjusting module. The output end of the bias voltage adjusting module is connected to a signal line between the sensor and the same-direction input end of the differential amplification circuit in parallel. The circuit of the utility model can actively control the zero point voltage output by the sensor, realizes accurate calibration, and can carry out zero setting on the temperature drift and the time drift of the sensor.

Description

Technical Field

[0001] The utility model relates to the technical field of sensors, in particular to a zero-voltage output bias control circuit for a sensor. Background Art

[0002] Analog signal sensors are often used in electronic devices, such as barometric pressure sensors, temperature sensors, current sensors, voltage sensors, etc.

[0003] In a respiration detection circuit, the analog sensor outputs a voltage signal, and the zero-point voltage (referring to the output voltage of the sensor under the condition of no external excitation (such as temperature, pressure, flow rate, etc.). This voltage value can be used as a calibration reference for subsequent compensation and correction of measurement results) is often very small and has a certain range of fluctuations. For example, for a barometric pressure sensor with a range of 1 kPa, the output at zero point (under standard atmospheric pressure) is ±10 mV. Signal acquisition units such as MCUs or DSPs and other integrated circuits with analog signal acquisition (ADC) functions can only acquire voltages within their operating voltage ranges, and the acquisition will be inaccurate near the lower limit and upper limit values within the voltage range that the MCU can acquire. In order to improve the acquisition accuracy, the output signal of the sensor will be amplified by a certain ratio before acquisition. A common method is to use a simple resistor voltage division to add a bias to the zero-point voltage of the sensor. For example, adding 12 mV makes the zero-point voltage of the sensor become 2 mV to 22 mV, all positive voltages. If the voltage acquisition range of the MCU is 0 to 3.3 V and the acquisition resolution is 0.8 mV, then after being amplified 150 times, the zero-point voltage of the sensor is 0.55 V to 3.3 V. When inhaling, the sensor detects that the barometric pressure drops by about 10 Pa, and the zero-point voltage of the sensor will drop by 0.5 mV and be amplified 150 times, that is, it drops by 75 mV. Any fluctuations in the zero-point voltage of the sensor will be amplified 150 times and acquired by the MCU.

[0004] The above solution can only fix the bias voltage. If the zero-point voltage is too high, the amplification factor will be limited, and the accuracy of signal acquisition cannot be improved, nor can the anti-interference ability. If the zero-point voltage is fixed at 1 mV, it can be amplified 3300 times, and the zero-point voltage of the sensor is 3.3 V. Each time inhaling, it drops by 3300 mV, and a larger change amount can achieve higher-precision inhalation detection.

[0005] There will be temperature drift and time drift in the zero-point output voltage of all sensors.

[0006] Temperature drift (thermal drift): The range of the zero-point voltage changes with temperature, such as 0.001% / °C.

[0007] Time drift: The range of the zero-point voltage changes over time, with a certain drift per month, such as 0.001% / month, or 0.001% / year.

[0008] The zero-point output of the sensor is always a voltage range, such as -10mV to +10mV, which may be larger or smaller. The signal acquisition system can usually only acquire positive voltage signals. To improve the acquisition accuracy, the output signal of the sensor needs to be amplified by a certain ratio. The larger the amplification factor, the greater the feedback of the signal change output by the sensor, and thus the higher the acquisition accuracy.

[0009] For all MCUs or other types of controllers, the analog signals they acquire have a voltage range and acquisition resolution. For example, the voltage acquisition range of the STM32F103 series MCU is 0 to 3.3V, and the acquisition resolution of the 12-bit ADC is about 0.8mV, that is, the minimum voltage value that can be acquired is 0.8mV. Data overflow is invalid when exceeding the range. If the zero-point output of the sensor is -10mV, a common method is to fix a positive bias voltage, such as 12mV, through a resistor voltage division circuit, so that the zero point of the sensor becomes 2mV. However, due to the consistency problem of the sensor, assume that there is another sensor in the same batch with a zero-point output of 10mV. Since the hardware design has a fixed voltage bias, a positive bias voltage of 12mV is also added. At this time, the zero-point voltage of the sensor is 22mV. After being amplified 150 times, it reaches the upper limit value of the MCU voltage acquisition, which is 3.3V. The voltage change output by the sensor will be amplified 150 times. If the zero-point output of the sensor can be actively controlled to 2mV, add a bias voltage when the zero-point output is lower than 2mV, and control the voltage reduction when the zero point is higher than 2mV. In this way, it can be fixed to be amplified 1650 times to reach the upper limit value of the MCU voltage acquisition, which is 3.3V. The voltage change output by the sensor will be amplified 1650 times. Compared with the former, the amplification factor is increased by 11 times. If the zero-point voltage of the sensor can be fixed and controlled at 0.2mV, it can be amplified 16500 times, and the accuracy is increased by 10 times. In theory, as long as the resolution of the ADC module is high enough, the method of actively controlling the bias voltage can infinitely improve the acquisition accuracy of small voltage signals.

[0010] Therefore, the adaptive active bias voltage control can control the zero-point voltage of the sensor to a set fixed value each time the device is powered on, without worrying about temperature drift and time drift. Summary of the Utility Model

[0011] The technical problem to be solved by the present utility model is to provide a bias control circuit for the zero-point voltage output of a sensor, which can actively increase or decrease the zero-point voltage of the sensor and can zero-adjust the temperature drift and time drift of the sensor, aiming at the deficiencies of the existing technology.

[0012] To solve the above technical problems, the technical solution adopted by the present utility model is as follows: A zero-voltage output bias control circuit for a sensor, including a sensor, the sensor is connected to a differential amplification circuit, the differential amplification circuit is connected to an ADC module, the ADC module is connected to a controller module, the controller module is connected to a DAC module, and the DAC module is connected to a bias voltage adjustment module; the output end of the bias voltage adjustment module is connected in parallel to the signal line between the sensor and the non-inverting input terminal of the differential amplification circuit.

[0013] In one implementation, the sensor is connected to a first voltage follower and a second voltage follower; the output end of the first voltage follower is connected to the inverting input terminal of the differential amplification circuit, and the second voltage follower is connected to the non-inverting input terminal of the differential amplification circuit. The voltage follower improves the driving ability and anti-interference ability of the output voltage of the sensor.

[0014] In one implementation, the bias voltage adjustment module includes a first circuit and a second circuit; the first circuit includes a fourth voltage follower, the non-inverting input terminal of the fourth voltage follower is connected to the output of the DAC module, and the inverting input terminal and the output terminal of the fourth voltage follower are connected to the anode of a first diode; the second circuit includes a fifth voltage follower, the non-inverting input terminal of the fifth voltage follower is connected to the output of the DAC module, and the inverting input terminal and the output terminal of the fifth voltage follower are connected to the cathode of a second diode; the cathode of the first diode and the anode of the second diode D2 are connected between the output terminal of the second voltage follower and the non-inverting input terminal of the differential amplification circuit.

[0015] In one implementation, the differential amplification circuit includes an operational amplifier, the inverting input terminal of the operational amplifier is connected to the output terminal of the operational amplifier through a first resistor; the inverting input terminal of the operational amplifier is connected to the ADC module through a second resistor, and the output terminal of the first voltage follower is connected in parallel between the second resistor and the ADC module.

[0016] In one implementation, the non-inverting input terminal of the operational amplifier is connected to the inverting input terminal and the output terminal of a third voltage follower through a third resistor, both the third resistor and the output terminal of the third voltage follower are connected to the ADC module, the non-inverting input terminal of the operational amplifier is connected to one end of a fourth resistor, and the other end of the fourth resistor is grounded; the cathode of the first diode and the anode of the second diode are connected between the output terminal of the second voltage follower and the non-inverting input terminal of the third voltage follower.

[0017] The present utility model can actively control the zero voltage of the output voltage of the sensor to achieve precise calibration.

[0018] In one implementation, the ADC module, the DAC module, and the controller module are integrated into one body.

[0019] In one implementation, the DAC module uses a DAC chip or a DC / DC chip.

[0020] Compared with the prior art, the beneficial effects of the present utility model are as follows: By using the control circuit of the present utility model, the zero voltage of the sensor output voltage can be actively controlled, so as to realize the precise calibration of the zero voltage of the sensor and zero the temperature drift and time drift of the sensor. Description of the Drawings

[0021] Figure 1 It is a circuit structure block diagram of an embodiment of the present utility model;

[0022] Figure 2 It is a circuit schematic diagram of an embodiment of the present utility model. Detailed Embodiments

[0023] To make the objectives, technical solutions and advantages of the embodiments of the present utility model clearer, the technical solutions in the embodiments of the present utility model will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are some but not all of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0024] The embodiment of the present utility model provides a zero voltage output bias control circuit for a sensor, as shown in Figure 1 and Figure 2As shown in the figure, it includes a sensor 10, a voltage follower 20, a voltage follower 30, a DAC (Digital-to-Analog Converter, an electronic device or circuit used to convert digital signals into corresponding analog signals. A DAC usually consists of a digital signal input terminal, an analog output terminal, and a control circuit. There is a DAC module inside the MCU. For example, the DAC module inside the MCU has a 12-bit resolution. When the set value is 4095, the MCU will generate a voltage output of 3.3V) module 40, a bias voltage adjustment module 50, a voltage follower 60, a differential amplifier circuit 70, an ADC (Analog-to-Digital Converter, which converts analog signals from the external environment (such as temperature, pressure, light intensity, etc. from sensors) into digital form so that a microprocessor or other digital circuits can process and analyze this data. When converting an analog signal into a digital signal, a computer can only process binary numbers 0 and 1. When collecting an analog voltage signal, it is first converted into a corresponding digital signal through the internal ADC function module. For example, the power supply of the MCU is 3.3V, and the internal ADC module has a 12-bit resolution. That is, when the input voltage signal is 3.3V, the maximum value after conversion into a digital signal is 4096, which is 2 to the power of 12) module 80, and a controller 90 (MCU). Among them, the sensor 10 is used to output a differential voltage signal. The voltage followers 20 and 30 are used as buffer stages to increase the driving force and anti-interference ability of the sensor output voltage. The ADC module 80 converts the analog voltage signal into a digital signal that can be read by the controller 90 (MCU). The DAC module 40 converts the digital signal output by the controller 90 (MCU) into an analog signal. The bias voltage adjustment module controls and adjusts the output voltage of the DAC module 40 and the output voltage of the voltage follower 20. The voltage follower 60 buffers and outputs the output signal of the bias voltage adjustment module 50. The differential amplifier circuit 70 amplifies the signals of the voltage follower 30 and the voltage follower 60.

[0025] The bias voltage control module 50 includes a first circuit and a second circuit. The first circuit includes a fourth voltage follower U5 and a first diode D1; the second circuit includes a fifth voltage follower U6 and a second diode D2. The first circuit is connected to the controller module 90 (MCU) through the DAC module, and the second circuit is connected to the controller module 90 (MCU) through the DAC module. The subsequent stage of the sensor 10 is connected to a first voltage follower U1 and a second voltage follower U3. A third voltage follower U4 is connected between the first circuit, the second circuit, and the differential amplifier U2.

[0026] The differential amplifier circuit includes a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, and an operational amplifier U2, where R1 = R4 and R2 = R3.

[0027] Figure 2In the figure, the system power supply voltage is the same. In the initial state, U1, U3, and U4 are all followers. Therefore, the original voltages Vn = Vd, Vp = Vc = Ve output by the sensor, and they are all less than Vcc (system power supply). To read the original values of Ve and Vd, the controller module controls the DAC module to make the output of DAC1 full scale, making Vb greater than Vc, and diode D2 is turned off. At this time, the voltage of Vc will not decrease; the MCU controls the output of DAC2 to be 0, making Va less than Vc, and diode D1 is turned off. At this time, Vc will not increase.

[0028] Due to the equal voltage between the front and rear stages of the voltage follower, the common-mode voltage output by the sensor (in differential signal processing circuits such as differential amplifiers, the common-mode voltage refers to the voltage component applied to both input signals at the same time. Corresponding to the embodiment of the present invention, Vn and Vp are the common-mode voltages) Vn voltage is equal to Vd voltage. Vp is equal to the voltage at the Vc point and is also equal to the voltage at the Ve point, Vn = Vd, Vp = Vc = Ve. After the ADC module converts the voltage signals of Vd and Ve into digital signals, it transmits them to the controller module for processing to judge the magnitude of their difference, that is, the differential-mode voltage (referring to the potential difference between signal lines. Corresponding to the embodiment of the present invention, Vp - Vn is the differential-mode voltage) (Ve) - (Vd) = (Vp) - (Vn). The output common-mode voltages Vn and Vp of the sensor are relatively large, generally 1 / 2 of the system power supply voltage, and are both less than the MCU power supply voltage. The set target difference (differential-mode voltage) to control them is fixed at Vm.

[0029] 1. When Vp - Vn, that is, (Ve) - (Vd) is less than Vm, a bias voltage needs to be added to point Vc. The controller module will control the DAC module to output the full-scale DAC1. After passing through the voltage follower U6, the voltage is Vb, and Vb > Vc, making the diode D2 cut off, and the voltage of Vc will not decrease. At the beginning of the first adjustment, assuming that the forward voltage drop Vf of the diode D2 in the forward-biased conduction state is fixed at 0.7V, the controller controls the DAC module to output DAC2 as the first voltage value greater than Vc + 0.7V. After passing through the voltage follower U5, the voltage is Va, and Va > Vc + 0.7V, so D1 conducts. At this time, Vc has increased the bias voltage. After passing through the follower U4, the voltage is Ve. The ADC module converts the voltage value of Ve to the controller module, and the controller module determines whether (Ve) - (Vd) is still less than Vm at this time. If it is still less than Vm, the second adjustment starts. The controller module controls the DAC module to output DAC2 as the second voltage value greater than the first voltage value. After passing through the voltage follower U5, the voltage is Va, and Va > Vc + 0.7V, so D1 conducts. At this time, Vc has increased the bias voltage. After passing through the follower U4, the voltage is Ve. The ADC module converts the voltage value of Ve to the controller module, and the controller module determines whether (Ve) - (Vd) is still less than Vm at this time. After multiple cyclic adjustments, finally, (Ve) - (Vd) = Vm. The adjustment of adding the bias voltage to Vp is completed.

[0030] 2. When Vp - Vn, that is, (Ve) - (Vd), is greater than Vm, it is necessary to reduce the voltage of Vc. The controller module will control the DAC module to output DAC2 as 0. After passing through the voltage follower U5, the voltage is also 0. Since Va < Vc, the diode D1 is cut off, so that the voltage of Vc will not increase. At the beginning of the first adjustment, assuming that the forward voltage drop Vf of the forward-biased conduction of the diode D2 is fixed at 0.7V, the controller controls the DAC module to output DAC1 as the first voltage value less than Vc - 0.7V. After passing through the voltage follower U6, the voltage is Vb. When the diode D2 is forward-biased and conducting, Vc = Vb + 0.7V = Ve. The ADC module converts the voltage value of Ve to the controller module, and the controller module determines whether (Ve) - (Vd) is still greater than Vm. Since Vb is less than Vc - 0.7V at this time, D2 conducts, which will pull down the voltage of Vc. After passing through the follower U4, the voltage is Ve. The ADC module converts the voltage value of Ve to the controller module, and the controller module determines whether (Ve) - (Vd) is still greater than Vm at this time. If it is still greater than Vm, the second adjustment begins. The controller module controls the DAC module to output DAC1 as the second voltage value less than the first voltage value. After passing through the voltage follower U6, the voltage is Vb. After Vb decreases again, Vc = Vb + 0.7V = Ve, so that Ve also decreases again. The ADC module converts the voltage value of Ve to the controller module, and the controller module determines whether (Ve) - (Vd) is still greater than Vm. After multiple adjustments in a loop, finally (Ve) - (Vd) = Vm, completing the adjustment of reducing the voltage of Vp.

[0031] Through the above steps, the zero voltage of the sensor output voltage can be actively controlled to achieve precise calibration.

[0032] When the controller module determines that Ve - Vd = Vm, it saves the control value of the control DAC module and stops calibration. The differential amplifier circuit amplifies the difference Vm of Ve - Vd, and then transmits it to the controller through the ADC module. The controller reads the converted data, completing a high-precision sensor signal reading.

[0033] (Vp - Vn), that is, the value of the zero voltage, is smaller. The amplification factor of the differential amplifier circuit can be designed to be larger. When there is a small change in the sensor signal, it will be amplified by a larger multiple. After the ADC module converts it, the threshold value judged by the controller module can be larger, the judgment error is smaller, and the precision is high.

[0034] All semiconductor devices have temperature drift and time drift. The same is true for sensors. The zero output voltage is different in regions with different temperatures. The sensor will also generate zero voltage drift after working for a long time. Through the above circuit, the active control of the zero voltage can be realized, and the temperature drift and time drift of the sensor can be zeroed.

[0035] Although the preferred embodiments of the present application have been described, additional changes and modifications can be made to these embodiments by those skilled in the art once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the present application.

[0036] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalent technologies, the present application is also intended to include these modifications and variations.

Claims

1. A zero-voltage output bias control circuit for a sensor, characterized in that, It includes a sensor, which is connected to a differential amplification circuit. The differential amplification circuit is connected to an ADC module, the ADC module is connected to a controller module, the controller module is connected to a DAC module, and the DAC module is connected to a bias voltage adjustment module. The output end of the bias voltage adjustment module is connected in parallel to the signal line between the sensor and the non-inverting input end of the differential amplification circuit.

2. The zero voltage output bias control circuit of the sensor according to claim 1, characterized in that, The ADC module, DAC module, and controller module are integrated into one body.

3. The zero voltage output bias control circuit of the sensor according to claim 1, characterized in that The DAC module uses a DAC chip or a DC / DC chip.

4. The zero - point voltage output bias control circuit of the sensor according to claim 1, characterized in that, The sensor is connected to a first voltage follower and a second voltage follower. The output end of the first voltage follower is connected to the inverting input end of the differential amplification circuit, and the second voltage follower is connected to the non-inverting input end of the differential amplification circuit.

5. The zero - point voltage output bias control circuit of the sensor according to claim 4, characterized in that, The bias voltage adjustment module includes a first circuit and a second circuit. The first circuit includes a fourth voltage follower. The non-inverting input end of the fourth voltage follower is connected to the output of the DAC module, and the inverting input end and the output end of the fourth voltage follower are connected to the anode of a first diode. The second circuit includes a fifth voltage follower. The non-inverting input end of the fifth voltage follower is connected to the output of the DAC module, and the inverting input end and the output end of the fifth voltage follower are connected to the cathode of a second diode. The cathode of the first diode and the anode of the second diode D2 are connected to the signal line between the output end of the second voltage follower and the non-inverting input end of the differential amplification circuit.

6. The zero - point voltage output bias control circuit of the sensor according to claim 4 or 5, characterized in that, The differential amplification circuit includes an operational amplifier. The inverting input end of the operational amplifier is connected to the output end of the operational amplifier through a first resistor. The inverting input end of the operational amplifier is connected to the ADC module through a second resistor, and the output end of the first voltage follower is connected in parallel between the second resistor and the ADC module.

7. The zero - point voltage output bias control circuit of the sensor according to claim 6, characterized in that, The non-inverting input end of the operational amplifier is connected to the inverting input end and the output end of a third voltage follower through a third resistor. Both the third resistor and the output end of the third voltage follower are connected to the ADC module. The non-inverting input end of the operational amplifier is connected to one end of a fourth resistor, and the other end of the fourth resistor is grounded. The cathode of the first diode and the anode of the second diode are connected to the signal line between the output end of the second voltage follower and the non-inverting input end of the third voltage follower.

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