A pressure temperature synergistic measurement method of a piezoresistive MEMS pressure sensor

Abstract

The application provides a pressure temperature collaborative measurement method of a piezoresistive MEMS pressure sensor, comprising the following steps: S1, switching the resistance connection mode of a MEMS sensor head of the piezoresistive MEMS pressure sensor through a MOS switch, and acquiring pressure and temperature signals in time; S2, eliminating the influence of pressure on temperature measurement by using an equivalent resistance Req; S3, based on a pre-stored temperature-pressure characteristic curve, compensating the temperature drift error in real time through a digital algorithm. The application realizes the collaborative measurement of pressure and temperature by using the piezoresistive MEMS sensor head pressure-sensitive resistor, and realizes the calibration and compensation of temperature and pressure through a digital algorithm; the design difficulty and process requirement of the piezoresistive temperature pressure integrated sensor chip for the piezoresistive MEMS sensor head and the signal conditioning circuit are reduced, the measurement accuracy of temperature and pressure is improved, and the development and manufacturing cost of the piezoresistive temperature pressure integrated sensor chip is reduced.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit design technology, and in particular to a method for co-measurement of pressure and temperature using a piezoresistive MEMS pressure sensor. Background Technology

[0002] In existing technologies, MEMS piezoresistive pressure sensors often employ complex mechanical structures (such as double-sided bonded sandwich structures) or additional temperature-sensitive elements (such as thermocouples, thermistors, etc.) to achieve coordinated temperature and pressure measurement, leading to the following problems:

[0003] 1. Cross-sensitivity and temperature drift: Temperature and pressure measurements can interfere with each other, a phenomenon known as cross-sensitivity, which can lead to inaccurate results. Some integrated sensors employ novel temperature-pressure integrated sensing mechanisms with spatial orthogonality, such as integrating in-plane thermoelectricity and out-of-plane piezoresistive forces, to suppress crosstalk in dual-parameter measurements. Others use structural design to isolate the operating temperatures of the temperature-sensitive and pressure-sensitive elements, ensuring both operate within their optimal temperature ranges. However, the optimal operating temperature ranges of the pressure-sensitive and temperature-sensitive elements may differ; the temperature-sensitive element may function normally, while the pressure-sensitive element may experience severe temperature drift or even failure. Currently, some sensors address this issue by increasing the contact area and heat transfer efficiency between the temperature-sensitive element and the measured medium, decreasing the contact area and heat transfer efficiency between the pressure-sensitive element and the measured medium, providing appropriate thermal isolation between the temperature-sensitive element and other components, and providing thermal compensation for the pressure-sensitive element. Since the resistance of the piezoresistor is significantly affected by temperature, traditional hardware compensation methods require additional thermal isolation structures or complex conditioning circuits, resulting in high manufacturing costs and difficulty in miniaturization.

[0004] 2. High process complexity: For example, using a double bonding process to prepare a cavity structure can reduce the risk of wafer breakage, but it requires temporary bonding sheets to be bonded to the substrate twice, making the process steps cumbersome; or the sensitivity can be improved by using a peninsula groove structure, but it requires a special layout of varistors, resulting in low process tolerance.

[0005] 3. Complex signal processing: Using multi-material arrays to establish a set of equations to decouple temperature and pressure requires multiple sets of detection materials, which is difficult to integrate and depends on high-precision algorithms. Summary of the Invention

[0006] To address the aforementioned issues, this invention aims to propose a method for coordinated pressure and temperature measurement using a piezoresistive MEMS pressure sensor. This method utilizes the piezoresistive resistor in the piezoresistive MEMS sensor head to achieve coordinated pressure and temperature measurement, and employs digital algorithms for temperature and pressure calibration and compensation. This reduces the design complexity and process requirements of the piezoresistive MEMS sensor head and signal conditioning circuitry in the integrated temperature and pressure sensor chip, improves the measurement accuracy of temperature and pressure, and lowers the development and manufacturing costs of the integrated temperature and pressure sensor chip.

[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0008] A method for coordinated pressure and temperature measurement using a piezoresistive MEMS pressure sensor includes the following steps:

[0009] S1. Switch the resistance connection mode of the MEMS meter head of the piezoresistive MEMS pressure sensor by a MOS switch to acquire pressure and temperature signals in a time-division manner.

[0010] S2. Eliminate the influence of pressure on temperature measurement by using the equivalent resistance Req;

[0011] S3. Based on the pre-stored temperature-pressure characteristic curve, temperature drift error is compensated in real time through digital algorithms.

[0012] Furthermore, the piezoresistive MEMS pressure sensor includes a piezoresistive MEMS meter, a MOS switch, a temperature measurement bridge, an instrumentation amplifier, a non-volatile memory, an analog-to-digital converter, a clock oscillator, a timing control circuit, an interface circuit, and control logic and compensation algorithm circuits. The piezoresistive MEMS meter is used to sense pressure and temperature. The temperature measurement bridge is a Wheatstone bridge composed of a conditioning circuit and the piezoresistive MEMS meter, used to measure temperature values. The MOS switch is used to switch circuit connections to achieve time-division sampling of temperature and pressure. The instrumentation amplifier is used to condition the voltage difference of the Wheatstone bridge, making its changes over the entire measurement range consistent with the voltage difference. The ADC operates at near full scale; the analog-to-digital converter samples and quantizes the amplified voltage to generate digital code values ​​corresponding to different temperatures and pressures; the clock oscillator generates the clock signal required for chip operation; the non-volatile memory stores the chip's adjustment coefficients and configuration values ​​of each module; the interface circuit enables communication between the chip and an external controller, facilitating the configuration of internal circuit modules and NVM data updates; the control logic and compensation algorithm circuit uses the temperature and pressure information collected by the analog-to-digital converter and the compensation algorithm in the NVM to perform real-time compensation for temperature and pressure, achieving coordinated measurement and compensation of pressure and temperature curves, as well as compensation for errors caused by offset and process deviations.

[0013] Furthermore, in pressure measurement mode, the piezoresistive MEMS meter consists of a Wheatstone bridge with four piezoresistive resistors R1, R2, R3, and R4 forming a quadrilateral structure. The common node of resistors R1 and R4 is connected to the power supply VDD, the common node of R2 and R3 is grounded, and nodes V1 and V2 serve as output terminals with an output voltage of V12.

[0014] Furthermore, the working process during pressure measurement is as follows: The piezoresistors are located in the arms of the Wheatstone bridge, and all four arms are composed of piezoresistors. When pressure is applied to the piezoresistors, the resistances R1 and R3 of two opposing piezoresistors increase, while the resistances R2 and R4 of two opposing piezoresistors decrease. According to Kirchhoff's laws and Ohm's law, when the bridge is balanced, the output voltage V12 = 0, i.e., R2:R1 = R4:R3. When pressure causes a change in the resistance of the strain gauges, the bridge becomes unbalanced, and the output voltage V12 is no longer zero. The relationship between the output voltage V12, the power supply voltage VDD, and the resistances is: V12 = VDD × (R1 ÷ (R1 + R2) - R3 ÷ (R3 + R4)). Under pressure, changes in R1, R2, R3, and R4 will cause changes in the result of this formula, i.e., the output voltage V12 will change with the resistance changes caused by pressure. When the output voltage of the bridge is measured, the corresponding pressure value can be obtained according to the calibration relationship.

[0015] Furthermore, in temperature measurement mode, the four piezoresistive MEMS meter head consists of four piezoresistive resistors R1, R2, R3, and R4 forming an equivalent resistance Req.

[0016] Furthermore, the resistance value of the equivalent resistance Req is determined by the series and parallel combination of the piezoresistors, ensuring that the symmetrical resistance changes of Req cancel each other out when the pressure changes.

[0017] Furthermore, the equivalent resistor Req, together with R5, R6, and R7 in the conditioning chip of the instrumentation amplifier, forms a quadrilateral Wheatstone bridge. The common node of resistor Req and R7 is connected to the power supply VDD, the common node of R5 and R6 is grounded, and nodes V3 and V5 serve as output terminals, with an output voltage of V35.

[0018] Furthermore, in the temperature measurement process: the resistor Req acts as a thermistor in one arm of the Wheatstone bridge, while the other three arms are fixed resistors R5, R6, and R7. When the temperature changes, the resistance of Req changes accordingly, disrupting the bridge balance. According to Kirchhoff's laws and Ohm's law, when the bridge is balanced, the output voltage V35 = 0, i.e., R5:Req = R7:R6. When pressure causes a change in the resistance of the strain gauge, the bridge loses its balance, and the output voltage V35 is no longer zero. The relationship between the output voltage V12, the power supply voltage VDD, and the resistances is: V35 = VDD × (Req ÷ (Req + R5) – R6 ÷ (R6 + R7)). Under the influence of temperature, changes in Req will cause changes in the result of this formula, i.e., the output voltage V35 will change with the resistance change caused by temperature. When the output voltage of the bridge is measured, the corresponding temperature value can be obtained according to the calibration relationship.

[0019] Furthermore, the digital compensation algorithm uses the temperature information collected by the ADC and the compensation algorithm in the NVM to perform real-time compensation on the pressure measurement results, thereby eliminating errors caused by temperature curvature, misalignment, and process deviations.

[0020] Beneficial effects: This invention utilizes the piezoresistive resistor of the piezoresistive MEMS sensor head to achieve coordinated measurement of pressure and temperature, and uses digital algorithms to achieve calibration and compensation of temperature and pressure; it reduces the design difficulty and process requirements of the piezoresistive MEMS sensor head and signal conditioning circuit of the integrated temperature and pressure sensor chip, improves the measurement accuracy of temperature and pressure, and reduces the development and manufacturing cost of the integrated temperature and pressure sensor chip. Attached Figure Description

[0021] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0022] Figure 1 This is a flowchart illustrating the steps of the pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor described in this embodiment of the invention.

[0023] Figure 2 This is a schematic diagram of the structure of the piezoresistive MEMS pressure sensor in the pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor described in the embodiment of the present invention;

[0024] Figure 3 This is the equivalent circuit of the pressure measurement mode in the pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor described in the embodiments of the present invention;

[0025] Figure 4 This is the equivalent circuit of the temperature measurement mode in the pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor described in the embodiments of the present invention;

[0026] Figure 5 This is the Req mode equivalent circuit in the pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor described in the embodiments of the present invention;

[0027] Figure 6 This is a typical instrumentation amplifier structure diagram in the pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor described in the embodiments of the present invention. Detailed Implementation

[0028] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0029] Piezoresistive MEMS pressure sensors are pressure sensors manufactured using microelectronics and microfabrication technologies. They operate based on the piezoresistive effect, and the specific principle is as follows:

[0030] Sensing element detects pressure: The sensing element of a piezoresistive MEMS pressure sensor is generally made of semiconductor materials such as single-crystal silicon. It is often a peripherally sealed and fixed elastic silicon planar diaphragm structure, with the silicon material on the back of the diaphragm removed to form an inverted quadrilateral pyramidal cavity. When pressure is applied to the sensing element, the diaphragm will undergo elastic deformation.

[0031] The piezoresistive effect causes a change in resistance: Semiconductor materials exhibit a piezoresistive effect, meaning that when subjected to stress, their internal crystal lattice structure deforms, causing changes in the mobility and concentration of charge carriers (electrons or holes), which in turn alters the material's resistivity. As pressure increases, resistance also increases, and this change is directly proportional to the pressure.

[0032] Wheatstone bridge detection of resistance changes: Typically, four high-precision semiconductor strain gauges (piezoresistive resistors) are arranged in the form of a Wheatstone bridge, placed near the edge or center of a planar diaphragm. In the absence of pressure, the bridge is in equilibrium, and the output is zero. When pressure is applied, causing a change in the resistance of the sensing element, the balance of the Wheatstone bridge is disrupted, resulting in a pressure-related voltage signal. For example, when the measured pressure is applied, the resistance of one pair of arms increases while the resistance of another pair decreases, causing the bridge to output an unbalanced voltage that changes linearly with the measured pressure.

[0033] Signal Conditioning and Output: The voltage signal output by the bridge circuit is usually very weak and needs to be amplified and processed by signal conditioning circuitry to facilitate subsequent signal processing, display, and transmission. Furthermore, since temperature changes also affect the resistance of semiconductor materials, the sensor typically integrates a temperature sensor and uses software or hardware-implemented temperature compensation algorithms to correct for resistance changes caused by temperature variations, thereby improving measurement accuracy.

[0034] Traditional piezoresistive temperature and pressure integrated sensor chips employ complex MEMS mechanical structures to simultaneously measure pressure and temperature while reducing the impact of cross-sensitivity, thermal isolation, and temperature drift issues. This increases the design and manufacturing cost of MEMS and also requires complex signal conditioning circuitry, further increasing design complexity and chip power consumption.

[0035] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0036] Example 1

[0037] Based on the design flaws of the existing technology mentioned above, see [reference] Figure 1-6 This embodiment of a pressure-temperature co-measurement method using a piezoresistive MEMS pressure sensor includes the following steps:

[0038] S1. Switch the resistance connection mode of the MEMS meter head of the piezoresistive MEMS pressure sensor by a MOS switch to acquire pressure and temperature signals in a time-division manner.

[0039] S2. Eliminate the influence of pressure on temperature measurement by using the equivalent resistance Req;

[0040] S3. Based on the pre-stored temperature-pressure characteristic curve, temperature drift error is compensated in real time through digital algorithms.

[0041] This embodiment utilizes the piezoresistive MEMS sensor head piezoresistive resistor to achieve coordinated measurement of pressure and temperature, and uses digital algorithms to achieve temperature and pressure calibration and compensation. This reduces the design difficulty and process requirements of the piezoresistive MEMS sensor head and signal conditioning circuit for the integrated temperature and pressure sensor chip, improves the measurement accuracy of temperature and pressure, and reduces the development and manufacturing cost of the integrated temperature and pressure sensor chip.

[0042] This embodiment achieves coordinated temperature and pressure measurement through time-division switching, an equivalent resistance model, and a digital compensation algorithm. Its advantages include: Time-division multiplexing architecture: Switching via a single MEMS meter and MOS switch avoids hardware redundancy in traditional dual-bridge parallel designs, reducing chip area and power consumption; Cross-sensitivity suppression: Utilizing the symmetry of the equivalent resistance Req to counteract pressure interference with temperature measurement avoids signal coupling problems inherent in independent thermistor and varistor designs; Dynamic compensation capability: Based on a pre-stored temperature-pressure curve, a digital algorithm corrects temperature drift errors in real time, significantly improving accuracy compared to hardware compensation.

[0043] In a specific example, the piezoresistive MEMS pressure sensor includes a piezoresistive MEMS meter, a MOS switch, a temperature measurement bridge, an instrumentation amplifier, a non-volatile memory, an analog-to-digital converter, a clock oscillator, a timing control circuit, an interface circuit, and control logic and compensation algorithm circuits. The piezoresistive MEMS meter is used to sense pressure and temperature. The temperature measurement bridge is a Wheatstone bridge composed of a conditioning circuit and the piezoresistive MEMS meter, used to measure temperature values. The MOS switch is used to switch circuit connections to achieve time-division sampling of temperature and pressure. The instrumentation amplifier is used to condition the voltage difference of the Wheatstone bridge, making it variable across the entire measurement range. The amplified voltage is sampled and quantized by the analog-to-digital converter (ADC) to generate digital code values ​​corresponding to different temperatures and pressures. The clock oscillator generates the clock signal required for chip operation. The non-volatile memory stores the chip's adjustment coefficients and configuration values ​​of each module. The interface circuit enables communication between the chip and an external controller, allowing for the configuration of internal circuit modules and NVM data updates. The control logic and compensation algorithm circuit uses the temperature and pressure information collected by the ADC and the compensation algorithm in the NVM to perform real-time compensation for temperature and pressure, achieving coordinated measurement and compensation of pressure and temperature curves, as well as compensation for errors caused by offset and process deviations.

[0044] This embodiment integrates a piezoresistive meter, a MOS switch, a signal conditioning circuit, a storage module, and a compensation algorithm. Its advantages include: Fully integrated solution: A single chip integrates signal acquisition, processing, and compensation functions, eliminating the need for external temperature-sensitive components or complex conditioning circuits, making it suitable for miniaturized applications (such as wearable devices); Modular design: Non-volatile memory (NVM) independently stores calibration parameters, supporting chip reuse and dynamic parameter updates, improving production line yield and flexibility; Low power optimization: Through time-division sampling and dynamic clock management, power consumption is reduced compared to traditional parallel acquisition solutions.

[0045] To achieve coordinated measurement of temperature and pressure, see [link to relevant documentation]. Figure 2 In this embodiment, pressure and temperature are measured in a time-division manner by combining S0, S1, S2, S3, S4, S5, R5, R6, R7 with a timing control circuit in the conditioning circuit.

[0046] In pressure measurement mode, such as Figure 2 As shown, switches S0, S4, and S5 are closed, while switches S1, S2, S3, and S4 are open. The voltage at node V7 is equal to the voltage at node V1, and the voltage at node V6 is equal to the voltage at node V2. Node V3 is connected to ground through switch S0. The equivalent circuit is shown below. Figure 3 As shown.

[0047] In a specific example, in pressure measurement mode, the piezoresistive MEMS meter consists of four piezoresistive resistors R1, R2, R3, and R4 forming a quadrilateral Wheatstone bridge. The common node of resistors R1 and R4 is connected to the power supply VDD, the common node of R2 and R3 is grounded, and nodes V1 and V2 serve as output terminals with an output voltage of V12.

[0048] In this embodiment, the pressure-mode varistor (R1-R4) forms a quadrilateral Wheatstone bridge; corresponding advantages: high sensitivity: the response sensitivity of the four-varistor full-bridge structure to pressure deformation is more than twice that of the half-bridge design; symmetry suppresses common-mode interference: R1-R4 are symmetrically distributed in the center of the silicon film, which cancels the common-mode noise caused by temperature gradient and improves the signal-to-noise ratio.

[0049] In a specific example, the working process when measuring pressure is as follows: A piezoresistor is located in one of the arms of a Wheatstone bridge. All four arms are composed of piezoresistors. When pressure is applied to the piezoresistor, the resistances R1 and R3 of two opposing piezoresistors increase, while the resistances R2 and R4 of two opposing piezoresistors decrease. According to Kirchhoff's laws and Ohm's law, when the bridge is balanced, the output voltage V12 = 0, i.e., R2:R1 = R4:R3. When pressure causes a change in the resistance of the strain gauges, the bridge becomes unbalanced, and the output voltage V12 is no longer zero. The relationship between the output voltage V12, the power supply voltage VDD, and the resistances is: V12 = VDD × (R1 ÷ (R1 + R2) - R3 ÷ (R3 + R4)). Under pressure, changes in R1, R2, R3, and R4 will cause this equation to change; that is, the output voltage V12 will change with the resistance changes caused by pressure. When the output voltage of the bridge is measured, the corresponding pressure value can be obtained according to the calibration relationship.

[0050] The pressure measurement in this embodiment is based on the linear relationship between the bridge output voltage and resistance change. Advantages include: linear response characteristics: the bridge output voltage and pressure deformation are linearly related (non-linearity <0.1% FS), simplifying the calibration process. Direct calibration capability: through the direct mapping relationship between V12 and pressure values, the algorithm fitting complexity is reduced, lowering computational resource requirements.

[0051] In temperature measurement mode, such as Figure 2 As shown, switches S0, S4, and S5 are open, and switches S1, S2, S3, and S4 are closed. The voltage at node V7 is equal to the voltages at nodes V3 and V4, and the voltage at node V6 is equal to the voltage at node V5. The equivalent circuit is as follows. Figure 4 As shown.

[0052] See a specific example. Figure 5 In temperature measurement mode, the four piezoresistive MEMS meter head, R1, R2, R3, and R4, form an equivalent resistance Req.

[0053] In this embodiment, the varistor is recombined into an equivalent resistance Req under temperature mode; corresponding advantages: hardware reuse: the MEMS meter head varistor is reused as a temperature sensor, eliminating the need for additional temperature-sensitive components (such as thermistors), reducing cost and packaging complexity; temperature isolation: through the symmetrical structure design of Req, the interference of pressure on temperature measurement is eliminated.

[0054] In a specific example, the equivalent resistance Req is determined by a series-parallel combination of varistors, ensuring that the symmetrical resistance changes of Req cancel each other out when the pressure changes.

[0055] The equivalent resistance Req in this embodiment is designed to symmetrically cancel out pressure changes; corresponding advantages include: cross-sensitivity suppression: pressure-induced resistance changes in R1-R4 are canceled out in Req (e.g., R1↑ and R3↑, R2↓ and R4↓), ensuring that Req only responds to temperature changes; high stability: the resistance of Req is not sensitive to process deviations (tolerance < ±1%), improving the repeatability of temperature measurements.

[0056] In practical implementation, when pressure is applied to the piezoresistive MEMS meter, the resistance of the two corresponding piezoresistive resistors increases (e.g., R1 and R3), while the resistance of the other two corresponding piezoresistive resistors decreases (e.g., R2 and R4). According to Formula 1, through proper design, the changes in R1 and R3 and R2 and R4 can be mutually canceled out, resulting in the resistance value of Req not changing with pressure. The temperature coefficient TC of the resistance can be used to measure the piezoresistive MEMS meter.

[0057] See a specific example. Figure 4 The equivalent resistor Req, together with R5, R6, and R7 in the conditioning chip of the instrumentation amplifier, forms a quadrilateral Wheatstone bridge. The common node of resistor Req and R7 is connected to the power supply VDD, the common node of R5 and R6 is grounded, and nodes V3 and V5 serve as output terminals, with an output voltage of V35.

[0058] The temperature measurement bridge in this embodiment consists of Req and fixed resistors (R5-R7); corresponding advantages: optimized temperature sensitivity: the fixed resistors R5-R7 are made of low temperature coefficient materials (such as thin film resistors), so that the bridge output only reflects the temperature change characteristics of Req (sensitivity > 0.5mV / ℃); anti-interference ability: the fixed resistors are placed in a low stress area to avoid the influence of mechanical deformation on temperature measurement.

[0059] In a specific example, during the temperature measurement process: Resistor Req acts as a thermistor in one arm of a Wheatstone bridge, while the other three arms are fixed resistors R5, R6, and R7. When the temperature changes, the resistance of Req changes accordingly, disrupting the bridge balance. According to Kirchhoff's laws and Ohm's law, when the bridge is balanced, the output voltage V35 = 0, i.e., R5:Req = R7:R6. When pressure causes a change in the resistance of the strain gauge, the bridge loses its balance, and the output voltage V35 is no longer zero. The relationship between the output voltage V12, the power supply voltage VDD, and the resistances is: V35 = VDD × (Req ÷ (Req + R5) – R6 ÷ (R6 + R7)). Under the influence of temperature, changes in Req will cause changes in the result of this formula, i.e., the output voltage V35 will change with the resistance change caused by temperature. When the output voltage of the bridge is measured, the corresponding temperature value can be obtained according to the calibration relationship.

[0060] The temperature measurement in this embodiment is based on the linear relationship between the bridge output voltage and the Req temperature change; corresponding advantages:

[0061] Temperature linearization: The temperature variation characteristics of Req are mapped with high precision through multi-point calibration and piecewise linear interpolation;

[0062] High signal-to-noise ratio: A low-pass filter is embedded in the temperature mode to suppress high-frequency noise.

[0063] In a specific example, the digital compensation algorithm uses the temperature information acquired by the ADC and the compensation algorithm in the NVM to perform real-time compensation on the pressure measurement results, thereby eliminating errors caused by temperature curvature, misalignment, and process deviations.

[0064] The digital algorithm in this embodiment compensates for temperature curvature, misalignment, and process deviations in real time; corresponding advantages:

[0065] Multi-dimensional compensation: Through table lookup or polynomial fitting, zero-point temperature drift (α), sensitivity temperature drift (β) and nonlinear error (γ) are corrected simultaneously, achieving an accuracy of ±0.1%FS across the entire temperature range.

[0066] Real-time performance: The compensation algorithm is executed synchronously with ADC sampling to meet the requirements of dynamic pressure measurement.

[0067] It should be noted that the instrumentation amplifier circuit in this embodiment mainly consists of a two-stage differential amplifier circuit. Operational amplifiers A1 and A2 are non-inverting differential inputs. Non-inverting inputs can significantly increase the circuit's input impedance and reduce the attenuation of weak input signals. Differential inputs allow the circuit to amplify only differential-mode signals, while only acting as a follower for common-mode input signals, thus improving the ratio of the amplitude of the differential-mode signal to the common-mode signal sent to the subsequent stage (i.e., the common-mode rejection ratio, CMRR). Therefore, in the differential amplifier circuit with operational amplifier A3 as the core component, while maintaining the same CMRR requirement, the precision matching requirements for resistors R3 and R4, and Rf and R5 can be significantly reduced, resulting in a better common-mode rejection capability for the instrumentation amplifier circuit compared to a simple differential amplifier circuit. Under the conditions of R1 = R2, R3 = R4, and Rf = R5, the gain of the circuit in this example is: G = (1 + 2R1 / Rg)Rf / R3. As can be seen from the formula, the circuit gain can be adjusted by changing the value of Rg. Figure 6 As shown.

[0068] The ADC circuit can use SAR ADC, ΣΔ ADC, dual-slope ADC, or other ADC structures suitable for low speed and low power consumption. The quantization bit depth of the ADC should be selected based on the system's accuracy requirements.

[0069] Since the application does not have high requirements for OSC frequency, the oscillation circuit can adopt a ring oscillator or relaxation oscillator structure, and generate the clock signal required by each module through a frequency divider circuit.

[0070] NVM (Non-Volatile Memory) is used to store the chip's adjustment coefficients and the configuration values ​​of each module. It can be EEPROM, MTP, OTP, fuse, or FLASH, and the choice can be made according to the specific process.

[0071] The digital interface circuit uses common data interfaces such as I2C, SPI, UART or 1-wire to realize communication between the chip and the external controller, and to realize the configuration of internal circuit modules and NVM data update.

[0072] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for coordinated pressure and temperature measurement using a piezoresistive MEMS pressure sensor, characterized in that, Includes the following steps: S1. Switch the resistance connection mode of the MEMS meter head of the piezoresistive MEMS pressure sensor by a MOS switch to acquire pressure and temperature signals in a time-division manner. The piezoresistive MEMS pressure sensor includes a piezoresistive MEMS meter, a MOS switch, a temperature measurement bridge, an instrumentation amplifier, a non-volatile memory, an analog-to-digital converter, a clock oscillator, a timing control circuit, an interface circuit, and control logic and compensation algorithm circuits. The piezoresistive MEMS meter is used to sense pressure and temperature. The temperature measurement bridge is a Wheatstone bridge composed of a conditioning circuit and the piezoresistive MEMS meter, used to measure temperature values. The MOS switch is used to switch circuit connections to achieve time-division sampling of temperature and pressure. The instrumentation amplifier is used to condition the voltage difference of the Wheatstone bridge so that its variation across the entire measurement range is close to the full scale of the ADC. The analog-to-digital converter samples and quantizes the amplified voltage to generate digital code values ​​corresponding to different temperatures and pressures. The clock oscillator is used to generate the clock signal required for chip operation; the non-volatile memory is used to store the chip's adjustment coefficients and the configuration values ​​of each module; the interface circuit is used to realize communication between the chip and the external controller, and to realize the configuration of internal circuit modules and NVM data updates; the control logic and compensation algorithm circuit uses the temperature and pressure information collected by the analog-to-digital converter and the compensation algorithm in the NVM to perform real-time compensation for temperature and pressure, realize the coordinated measurement and compensation of pressure and temperature curves, and compensate for errors caused by offset and process deviation; in pressure measurement mode, the piezoresistive MEMS meter is composed of four piezoresistive resistors R1, R2, R3, and R4 forming a quadrilateral Wheatstone bridge, the common node of resistors R1 and R4 is connected to the power supply VDD, the common node of R2 and R3 is grounded, and nodes V1 and V2 are used as output terminals, with an output voltage of V12; The input terminal of the instrumentation amplifier is connected to the output terminals of the pressure and temperature measurement bridges formed by the MEMS meter via a time-division multiplexing MOS switch. The output terminal of the instrumentation amplifier is connected to an analog-to-digital converter (ADC), and the output terminal of the ADC is connected to a control logic and compensation algorithm circuit. The control logic and compensation algorithm circuit is connected to a non-volatile memory and an interface circuit, respectively. The timing control circuit is connected to the MOS switch to control its on / off switching. The MOS switch includes six switches S0, S1, S2, S3, S4, and S5. The conditioning circuit includes fixed resistors R5, R6, and R7. One end of S0 is connected to node V3 and the other end is grounded. One end of S1 is connected to node V4 and the other end is grounded. Connect node V3, connect one end of S2 to node V7 and the other end to node V4, connect one end of S3 to node V5 and the other end to node V6, connect one end of S4 to node V2 and the other end to node V6, connect one end of S5 to node V1 and the other end to node V7. Nodes V7 and V6 are respectively connected to the positive and negative input terminals of the instrumentation amplifier. The control input terminals of switches S0, S1, S2, S3, S4, and S5 are all connected to the timing control circuit. The connection relationship of the fixed resistors is as follows: the upper end of R5 is connected to node V4 and the lower end is grounded; the upper end of R6 is connected to node V5 and the lower end is grounded; the upper end of R7 is connected to the power supply VDD and the lower end is connected to node V5. In temperature measurement mode, the four piezoresistive MEMS meter components R1, R2, R3, and R4 form an equivalent resistance Req. The resistance value of Req is determined by the series and parallel combination of the piezoresistive resistors, ensuring that the symmetrical resistance changes of Req cancel each other out when the pressure changes. ; The equivalent resistor Req, together with R5, R6, and R7 in the conditioning chip of the instrumentation amplifier, forms a quadrilateral Wheatstone bridge. The common node of resistor Req and R7 is connected to the power supply VDD, the common node of R5 and R6 is grounded, and nodes V3 and V5 serve as output terminals with an output voltage of V35. In the temperature measurement process: Resistor Req acts as a thermistor in one arm of a Wheatstone bridge, while the other three arms are fixed resistors R5, R6, and R7. When the temperature changes, the resistance of Req changes accordingly, disrupting the bridge balance. According to Kirchhoff's laws and Ohm's law, when the bridge is balanced, the output voltage V35 = 0, i.e., R5:Req = R7:R6. When pressure causes a change in the resistance of the strain gauge, the bridge loses its balance, and the output voltage V35 is no longer zero. The relationship between the output voltage V12, the power supply voltage VDD, and the resistances is: V35 = VDD × (Req ÷ (Req + R5) – R6 ÷ (R6 + R7)). Under the influence of temperature, changes in Req will cause changes in the result of this formula, i.e., the output voltage V35 will change with the resistance change caused by temperature. When the output voltage of the bridge is measured, the corresponding temperature value can be obtained according to the calibration relationship. S2. Eliminate the influence of pressure on temperature measurement by using the equivalent resistance Req; S3. Based on the pre-stored temperature-pressure characteristic curve, the temperature drift error is compensated in real time through a digital compensation algorithm.

2. The pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor according to claim 1, characterized in that, The working process during pressure measurement: The varistor is located in one of the arms of a Wheatstone bridge. All four arms are composed of varistors. When pressure is applied to the varistor, the resistances R1 and R3 of two opposite varistors increase, while the resistances R2 and R4 of two opposite varistors decrease. According to Kirchhoff's laws and Ohm's law, when the bridge is balanced, the output voltage V12 = 0, i.e., R2:R1 = R4:R3. When pressure causes a change in the resistance of the strain gauges, the bridge becomes unbalanced, and the output voltage V12 is no longer zero. The relationship between the output voltage V12, the power supply voltage VDD, and the resistances is: V12 = VDD × (R1 ÷ (R1 + R2)) R3÷(R3+R4); Under pressure, changes in R1, R2, R3, and R4 will cause the result of this formula to change, that is, the output voltage V12 will change with the change in resistance caused by pressure. When the output voltage of the bridge is measured, the corresponding pressure value can be obtained according to the calibration relationship.

3. The pressure-temperature co-measurement method of the piezoresistive MEMS pressure sensor according to claim 1, characterized in that, The digital compensation algorithm uses the temperature information collected by the ADC and the compensation algorithm in the NVM to compensate for the pressure measurement results in real time, thereby eliminating errors caused by temperature curvature, misalignment, and process deviations.

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