Sensing thermal gas flow sensor mems chip end and linear compensation circuit

Abstract

The application relates to a sensing thermal type gas flow sensor MEMS chip end, a heating wire is located at a center symmetrical position of a heat insulation bridge; an adiabatic cavity is arranged at the bottom of the heat insulation bridge, the adiabatic cavity is connected with the heat insulation bridge at two ends in the vertical direction along the arrangement direction of the heating wire; the outside of the adiabatic cavity is a substrate; first and second temperature sensitive resistance type sensors are connected in series to form a half-arm Wheatstone bridge and are located at equidistant positions of two ends of the heating wire and on the heat insulation bridge; first and second BJT bipolar transistors are combined on the substrate on two sides of the adiabatic cavity along the arrangement direction of the central heating wire; and the distances from the heating wires are equal, they respectively include a first BJT transistor and a second BJT transistor and respectively include a third BJT transistor and a fourth BJT transistor. The disclosure uses a mathematical principle to convert a quadratic curve with constant curvature characteristics into a cubic curve with a curvature passing through 0 point characteristics to complete compensation. In the range of the scale, the curve is approximately a straight line.

Description

Technical Field

[0001] This invention relates to the technical fields of MEMS semiconductor devices and CMOS semiconductor devices, and particularly to a MEMS thermal gas flow sensor and its compensation circuit. Background Technology

[0002] Traditional MEMS thermal flow sensors consist of two parts: a gas flow velocity sensor comprised of a central heating wire and a heating compensation circuit, and an output sensor that measures the heating coil of the central heating wire. This structure exhibits good output linearity at low gas flow rates, but at high gas flow rates, the heating capacity of the heating wire is gradually weakened by the rapidly flowing gas. Therefore, traditional MEMS thermal gas flow sensors experience a decrease in sensitivity and linearity when measuring high-velocity gases. Current solutions to this problem often involve back-end compensation, such as using a computer or MCU to recalibrate and calculate the sensor's output voltage value. However, traditional compensation algorithms based on digital computing systems are complex and costly to implement, making them unsuitable for applications with strict requirements on size, power consumption, and cost. Summary of the Invention

[0003] One of the technical problems that this disclosure aims to solve is to improve the linearity of the output voltage.

[0004] To address the aforementioned technical problems, this disclosure provides a MEMS chip for a heat-sensing gas flow sensor, comprising: a substrate, wherein the substrate is a single-crystal silicon wafer with a crystal orientation of 100; and further comprising: a central heating wire 101, a first temperature-sensitive resistive sensor 1021, a second temperature-sensitive resistive sensor 1022, a first BJT bipolar transistor assembly, a second BJT bipolar transistor assembly, and a thermal bridge 106; the central heating wire 101 is located at the central axis of symmetry on the thermal bridge 106; and an insulating cavity 10 is located at the bottom of the thermal bridge 106. 5. The insulating cavity 105 is connected to the thermal insulation bridge 106 at both ends perpendicular to the direction of the central heating wire 101; the exterior of the insulating cavity 105 is a substrate; the first temperature-sensitive resistor sensor and the second temperature-sensitive resistor sensor are connected in series to form a half-arm Wheatstone bridge and are located at equidistant positions at both ends of the central heating wire 101 and on the thermal insulation bridge; the first BJT bipolar transistor assembly and the second BJT bipolar transistor assembly are located on the substrates on both sides of the insulating cavity 105 along the direction of the central heating wire 101; the first BJT bipolar transistor... The first BJT bipolar transistor assembly and the second BJT bipolar transistor assembly are equidistant from the heating wire. The first BJT bipolar transistor assembly includes a first BJT transistor and a second BJT transistor, wherein the collectors and bases of the N basic BJT transistor units of the first BJT transistor are short-circuited and connected in parallel, and the collectors and bases of the M basic BJT transistor units of the second BJT transistor are short-circuited and connected in parallel; the emitters of the N basic BJT transistor units of the first BJT transistor are connected in parallel, and the emitters of the M basic BJT transistor units of the second BJT transistor are connected in parallel. The emitters of the first-order BJT transistors are connected in parallel; the second BJT bipolar transistor combination includes a third BJT transistor and a fourth BJT transistor, wherein the collectors and bases of the N basic BJT transistor units of the third BJT transistor are short-circuited and connected in parallel, and the collectors and bases of the M basic BJT transistor units of the fourth BJT transistor are short-circuited and connected in parallel; the emitters of the N basic BJT transistor units of the third BJT transistor are connected in parallel, and the emitters of the M basic BJT transistor units of the fourth BJT transistor are connected in parallel; N is greater than or equal to 2, and M is greater than or equal to 1.

[0005] In some embodiments, the first BJT bipolar transistor combination is a first PNP BJT transistor combination 1031; the second BJT bipolar transistor combination is a second PNP BJT bipolar transistor combination 1032; the first PNP BJT transistor combination 1031 and the second PNP BJT bipolar transistor combination 1032 have the same structure.

[0006] In some embodiments, the insulation cavity of the insulation cavity 105 is in the shape of an inverted frustum.

[0007] In some embodiments, the system further includes an ambient temperature sensor 104 and a heating wire constant temperature difference control module. The ambient temperature sensor 104 is connected to the heating wire constant temperature difference control module. The center heating wire 101, the first temperature-sensitive resistor sensor 1021, and the second temperature-sensitive resistor sensor 1022 are made of platinum metal, and the thermal bridge 106 is made of silicon dioxide or silicon nitride.

[0008] To address the aforementioned technical problems, this disclosure also provides a linear compensation system for a thermally sensing gas flow sensor, including the aforementioned thermally sensing gas flow sensor MEMS chip, and further comprising: a first loop, a first shunt circuit, a second loop, and a second shunt circuit; the first output terminal of the first loop is connected to the input terminal of a first BJT transistor, and the second output terminal of the first loop is connected to the input terminal of a second BJT transistor; the shunt terminal of the first loop is connected to the input terminal of the first shunt circuit, and the output terminal of the first shunt circuit is connected to the input terminal of a first temperature-sensitive resistive sensor 1021; the first output terminal of the second loop is connected to the input terminal of a third BJT transistor, and the second output terminal of the second loop is connected to the input terminal of a fourth BJT transistor; the shunt terminal of the second loop is connected to the input terminal of the second shunt circuit, and the output terminal of the second shunt circuit is connected to the input terminal of a second temperature-sensitive resistive sensor 1022.

[0009] In some embodiments, a loop starter is further included; the loop starter drives the first loop and the second loop to operate respectively; the first loop includes a first voltage-controlled current generator, a first voltage differencer, and a first load impedance; the first current output terminal of the first voltage-controlled current generator flows through the first load impedance and a first BJT transistor, and the second current output terminal of the first voltage-controlled current generator flows through a second BJT transistor; the sum of the voltages of the first load impedance and the first BJT transistor is connected to the first input terminal of the first voltage differencer, the voltage output terminal of the second BJT transistor is connected to the second input terminal of the first voltage differencer, and the output terminal of the first voltage differencer is connected to the control terminal of the first voltage-controlled current generator; the second loop includes a second voltage-controlled current generator, a second voltage differencer, and a second load impedance; the first current output terminal of the second voltage-controlled current generator flows through a third BJT transistor. The second current output terminal of the second voltage-controlled current generator flows through the second load impedance and the fourth BJT transistor; the sum of the voltages of the third BJT transistor is connected to the first input terminal of the second voltage differencer, the voltage output terminals of the second load impedance and the fourth BJT transistor are connected to the second input terminal of the second voltage differencer, and the output terminal of the second voltage differencer is connected to the control terminal of the second voltage-controlled current generator; the first shunt circuit is a first current amplifier, and the second shunt circuit is a second current amplifier; the output terminal of the first voltage differencer is connected to the input terminal of the first current amplifier, the output terminal of the first current amplifier is connected to the non-series terminal of the first temperature-sensitive resistor sensor 1021, the output terminal of the second voltage differencer is connected to the input terminal of the second current amplifier, and the output terminal of the second current amplifier is connected to the non-series terminal of the second temperature-sensitive resistor sensor 1022.

[0010] To address the aforementioned technical problems, this disclosure also provides a linear compensation system for a thermally sensing gas flow sensor, including the aforementioned thermally sensing gas flow sensor MEMS chip, and further comprising: a first loop, a first replication circuit, a second loop, and a second replication circuit; the first output terminal of the first loop is connected to the input terminal of a first BJT transistor, and the second output terminal of the first loop is connected to the input terminal of a second BJT transistor; the first replication circuit replicates the current of either the first or second BJT transistor; the output terminal of the first replication circuit is connected to the input terminal of a first temperature-sensitive resistive sensor 1021; the first output terminal of the second loop is connected to the input terminal of a third BJT transistor, and the second output terminal of the second loop is connected to the input terminal of a fourth BJT transistor; the second replication circuit replicates the current of either the third or fourth BJT transistor; and the output terminal of the second replication circuit is connected to the input terminal of a second temperature-sensitive resistive sensor 1022.

[0011] In some embodiments, the system further includes a first loop, a second loop, and a loop starter; the loop starter drives the first loop and the second loop to operate respectively; the first loop includes a first voltage-controlled current generator, a first voltage differencer, and a first load impedance; the first current output terminal of the first voltage-controlled current generator flows through the first load impedance and a first BJT transistor, and the second current output terminal of the first voltage-controlled current generator flows through the second BJT transistor; the sum of the voltages of the first load impedance and the first BJT transistor is connected to the first input terminal of the first voltage differencer, the voltage output terminal of the second BJT transistor is connected to the second input terminal of the first voltage differencer, and the output terminal of the first voltage differencer is connected to the control terminal of the first voltage-controlled current generator; the second loop includes a second voltage-controlled current generator, a second voltage differencer, and a second load impedance; the first current output terminal of the second voltage-controlled current generator... The current flows through the third BJT transistor, and the second current output terminal of the second voltage-controlled current generator flows through the second load impedance and the fourth BJT transistor; the voltage output terminal of the third BJT transistor is connected to the first input terminal of the second voltage differencer, the sum of the voltages of the second load impedance and the fourth BJT transistor is connected to the second input terminal of the second voltage differencer, and the output terminal of the second voltage differencer is connected to the control terminal of the second voltage-controlled current generator; the first replication circuit is a first current replication circuit, and the second replication circuit is a second current replication circuit; the first current replication circuit replicates the emitter current of the first BJT transistor, and the second current replication circuit replicates the emitter current of the fourth BJT transistor; the output terminals of the first current replication circuit and the second current replication circuit are respectively connected to the non-series terminals of the first temperature-sensitive resistive sensor 1021 and the second temperature-sensitive resistive sensor 1022.

[0012] In some embodiments, a current reference source is further included, which is used to drive a first voltage differencer and a second voltage differencer.

[0013] To address the aforementioned technical problems, this disclosure also provides a linear compensation system for a thermally sensing gas flow sensor, including the aforementioned thermally sensing gas flow sensor MEMS chip. The heating wire constant temperature difference control module includes: a first voltage divider, a second voltage divider, and a third voltage difference calculator. The first voltage divider includes a first external resistor Ra, one end of which is connected in series with an ambient temperature sensor 104. The second voltage divider includes a second external resistor Rb, one end of which is connected in series with a central heating wire 101. The other ends of the first and second external resistors Ra and Rb are connected. The other ends of the ambient temperature sensor 104 and the central heating wire 101 are grounded. The connection between the first external resistor Ra and the ambient temperature sensor 104 is connected to the first input terminal of the third voltage difference calculator. The connection between the second external resistor Rb and the central heating wire 101 is connected to the second input terminal of the third voltage difference calculator. The output terminal of the third voltage difference calculator is connected to the connection between the first and second external resistors Ra and Rb.

[0014] Through the above technical solution, this disclosure utilizes mathematical principles to convert a quadratic curve with constant curvature into a cubic curve with curvature passing through zero to complete the compensation. At the circuit design level, this system is based on a CMOS integrated analog circuit architecture. It uses a combination of BJT transistors in the MEMS chip and a linear compensation circuit to generate an output current with a linear relationship to the gas flow rate. This current is then input to the thermistor voltage divider circuit in the original sensor, which has a quadratic relationship to the gas flow rate. Finally, a voltage output curve with a cubic relationship to the gas flow rate is output. Because the thermal conductivity of the silicon substrate in this invention is much higher than that of the thermal bridge, the first and second temperature-sensitive resistor sensors are close to the heat-conducting wire, while the first and second BJT bipolar transistor combinations are far from the heat-conducting wire. Within the measurement range, this curve approximates a straight line. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a block diagram of the MEMS chip terminal of the bidirectional sensing thermal gas flow sensor of the present invention and its linear compensation circuit system.

[0017] Figure 2 This is a schematic diagram of the loop starter submodule;

[0018] Figure 3 This is a flowchart of the system's workflow for a given gas flow direction.

[0019] Figure 4 The next system workflow diagram for a different gas flow direction;

[0020] Figure 5 This is one embodiment of the MEMS chip side of the bidirectional sensing thermal gas flow sensor of the present invention;

[0021] Figure 6 This is a cross-sectional view of an embodiment of the bidirectional thermal gas flow sensor MEMS chip of the present invention;

[0022] Figure 7 This is a circuit diagram of a first embodiment of the linear compensation circuit for the bidirectional thermal gas flow sensor of the present invention.

[0023] Figure 8 This is a circuit diagram of a second embodiment of the linear compensation circuit for the bidirectional sensing thermal gas flow sensor of the present invention.

[0024] Figure 9 This is a circuit diagram of Embodiment 3 of the linear compensation circuit for the bidirectional sensing thermal gas flow sensor of the present invention.

[0025] Figure 10 This is a circuit diagram of Embodiment 4 of the linear compensation circuit for the bidirectional sensing thermal gas flow sensor of the present invention.

[0026] Figure 11 This is a circuit diagram of embodiment five of the linear compensation circuit for the bidirectional thermal gas flow sensor of the present invention.

[0027] Figure 12 This is an important theoretical basis for the wind speed / temperature difference fitting curve in this invention;

[0028] Figure 13 Therefore, the system compares the output signal and the compensation signal before compensation based on simulation.

[0029] Figure 14 Therefore, the system's output signal fitting curve before compensation and the compensation signal fitting curve are shown.

[0030] Figure 15 This is a schematic diagram of the curve after system compensation. Detailed Implementation

[0031] The embodiments of this disclosure will be further described in detail below with reference to the accompanying drawings and examples. The detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of this disclosure by way of example, but should not be used to limit the scope of this disclosure. This disclosure can be implemented in many different forms and is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

[0032] This invention includes MEMS chip-side design and linear compensation circuit-side design. Compared to traditional thermal gas flow meters, this invention improves the MEMS chip-side design by adding two sets of two BJT transistors each on a substrate at equidistant positions at both ends of the heating wire, thus incorporating the original temperature difference relationship from the MEMS sensor chip. This temperature relationship is converted into current in the accompanying circuit, and multiplicative compensation based on analog circuitry is performed using the relationship: output voltage = current * resistance. Detailed explanations of the mathematical and analog circuit design are provided below.

[0033] During their research, the inventors discovered that as the inflow gas flow rate increases, the temperature difference between two points equidistant from the ends of the heating wire in a thermal gas flow sensor can be fitted to a quadratic curve with respect to the gas flow rate. The curvature and peak value of this quadratic curve can be altered by external conditions: the closer the two points are to the heating wire, the higher the gas flow rate required to reach the peak value of the quadratic curve; the higher the thermal conductivity at the location of the two points, the lower the curvature of the quadratic curve.

[0034] Therefore, this wind speed / temperature difference curve relationship can be used to transform the region near the peak of a quadratic function into a cubic function. Regarding the principle behind this curve transformation, the inventors mathematically discovered that quadratic curves such as y=a*x²+b*x+c possess slope and curvature properties, as shown in eq.1 and eq.2.

[0035] eq.1

[0036] eq.2

[0037] Multiplying this quadratic curve by the linear curve yields a cubic curve, such as y = dx³ + ex² + fx + g, which has slope and curvature properties, as shown in equations 3 and 4.

[0038] eq.3

[0039] eq.4

[0040] The cubic curve can be derived from the point using the curvature calculation of eq.4. That is, the curvature is 0, which transforms the concavity / convexity. Near this point, the point function of this cubic curve approximates a linear function because the curvature is approximately 0. Compared to the original quadratic function, which has a constant curvature of 2*a, although a lower curvature can be achieved by setting the value of 'a', it is difficult to achieve while maintaining other properties of the function. Therefore, when the curvature is approximately 0, the derivative of the cubic function in eq.3 is approximately j, approaching the characteristics of a linear function. The above mathematical foundation forms the basis of the first mathematical theory. The inventor also discovered in mathematical research that when two quadratic curves are multiplied, if their curvatures and peak values ​​differ significantly, a portion resembling a cubic curve can be produced. A brief explanation follows, assuming there are two quadratic curves.

[0041] eq.5

[0042] Where a1, b1 and a2, b2 are all positive numbers (a1 / a2>=10.247), and a1 and a2 are related to thermal conductivity. In this invention, the thermal conductivity of the silicon substrate is greater than that of the thermal bridge (λ). 硅衬底 / λ 隔热桥 >=10 (as in Examples 1-5, the thermal conductivity of silicon is 0.21 W / m·K, and on the thermal bridge it is 0.0267 W / m·K). And b1 is greater than b2 (b1 / b2>=8), where b1 and b2 are related to the position of the peak value. The first and second temperature-sensitive resistor sensors are located 10-50 μm away from both ends of the heating wire (10-50 μm for a single temperature-sensitive resistor, and 10-50 μm away from the nearest "S"-shaped temperature-sensitive resistor if there are two or more). The first and second BJT bipolar transistor combinations are located 1300-2000 μm away from both ends of the heating wire. Therefore, compared to the first curve containing parameters a1 and b1, the second curve containing parameters a2 and b2 can be considered a linear curve.

[0043] When b1 is much larger than b2, the peak value of the second curve is far from the peak value of the first curve. At this point, the area near x=b1 is the monotonically decreasing interval of the second curve, and the slope and curvature of the second curve are...

[0044] eq.6

[0045] eq.7

[0046] As shown in eq.6 and eq.7, compared to the first curve, the second curve can be considered a linear function under this condition. The above mathematical foundations form the basis of the second mathematical theory.

[0047] The design principle of this integrated analog linear compensation circuit is based on the above mathematical ideas, and the compensation algorithm is implemented using analog circuits. In the formula shown in Eq.5, the parameters a1 and b1 in the high curvature quadratic curve can be realized by the first temperature-sensitive resistor sensor and the second temperature-sensitive resistor sensor proposed above, and the parameters a2 and b2 in the high curvature quadratic curve can be realized by the first BJT bipolar transistor combination and the second BJT bipolar transistor combination proposed above and the compensation circuit in this invention.

[0048] Meanwhile, utilizing the multiplicative calculation characteristic of voltage = current * resistance, and the quadratic relationship between wind speed and temperature difference, a quadratic function is introduced. Different thermal conductivity and peak values ​​are used to convert the quadratic wind speed / temperature difference curve at the temperature sensor of the compensation current source into a linear curve to achieve the compensation effect. Specifically, two points equidistant on both sides of the heating wire and within the substrate have high thermal conductivity and are far from the heating wire, making them less susceptible to temperature difference changes due to increased wind speed. Two points equidistant on both sides of the heating wire and on the thermal bridge have low thermal conductivity and are close to the heating wire, making them less susceptible to temperature difference changes due to increased wind speed. The temperature difference curves at these two locations satisfy the second mathematical theoretical basis. Connecting these two curves to the changes in current and resistance, and ultimately outputting a voltage, satisfies the first mathematical theoretical basis. The following briefly describes the theoretical method of connecting these mathematical theories through analog integrated circuit design. Two sets of thermistors are placed on the thermal bridge at equidistant positions on both sides of the heating wire to form a single-arm Wheatstone bridge. The two ends of this bridge are connected to the current input and ground, respectively, with the center connection point being the output. This output voltage is...

[0049] eq.8

[0050] Where R is the resistance of the temperature-sensitive resistor at the reference temperature, α is the temperature coefficient of resistance, ΔT1 is the temperature difference between one thermistor and the reference temperature after being heated by the heating wire, ΔT2 is the temperature difference between the other thermistor and the reference temperature after being heated by the heating wire, and Iin is the input current. Considering that the operating principle of this heating wire-Wheatstone thermistor bridge system is that one side heats up while the other side cools down, an intermediate value ΔT3 can be taken to simplify the above formula.

[0051] eq.9

[0052] Where ΔT3 is the temperature difference between the two thermistor positions when no gas flows and when gas flows. When the gas flow rate changes, the gas flow rate and this temperature difference ΔT3 form a quadratic curve, such as ΔT3 = a*vg² + b*vg + c. Since the output voltage V and ΔT3 form a linear system, the output voltage curve is also a quadratic curve, corresponding to the first mathematical theoretical foundation. The output voltage / input current curve is also a quadratic curve, and because the thermal bridge is less prone to temperature loss, this quadratic curve has a high curvature.

[0053] eq.10

[0054] Considering that the thermal conductivity of the silicon substrate is much higher than that of the thermal bridge, another low curvature curve can be constructed. A first PNP type BJT bipolar transistor assembly and a second BJT bipolar transistor assembly are fabricated in the substrate using CMOS technology to form another temperature difference-current sensitive circuit. Here, the characteristic of BJT bipolar transistors is utilized: the voltage difference between the base and emitter of two BJT transistors operating at different currents (such as BJT transistors Q1, Q2 or Q3, Q4 in Examples 1-5) is positively correlated with temperature.

[0055] eq.11

[0056] Where I1 and I2 are the base-emitter currents of the two BJT transistors, Is1 and Is2 are the inverting saturation currents of the two BJT transistors, and V T The thermal voltage is the temperature voltage of the two BJT transistors. Since the inverting saturation current depends only on temperature and the two BJT transistors are at the same temperature, and the thermal voltage V... T In the equation =k*T / q, k and q are both constants. Assuming I2:I1 is a constant value N, the following formula can be written:

[0057] eq.12

[0058] Based on this relationship, a resistor R is added to the branch with current I1. Now, if an external circuit is used to ensure that the voltage across the second BJT transistor equals the voltage across the first BJT transistor plus the voltage across the resistor, this temperature / voltage linear relationship can be transformed into a temperature / current linear relationship, as shown in the following formula.

[0059] eq.13

[0060] Where R is a load impedance device carrying current I1, which can be a resistor, MOSFET, capacitor, inductor, etc. Transforming the above equation, we get...

[0061] eq.14

[0062] Similarly, substituting the thermal voltage V T =k*T / q, where I2:I1 is a constant value N, and the following formula can be written:

[0063] eq.15

[0064] If two sets of the above temperature / current circuits are designed and placed side-by-side in the substrate with equidistant points at both ends of the central heating wire, and the currents in opposite directions are connected, a temperature difference / current relationship can be established. Assuming that another temperature / current source generating circuit, I3 and I4, corresponds to the current relationship I2 and I1 respectively, and I3:I4 is a constant value N...

[0065] eq.16

[0066] ΔT is related to wind speed in the form ΔT = a*vg² + b*vg + c, and this temperature / current circuit system is also a linear system. diff The relationship with wind speed is also quadratic. However, because the BJT bipolar transistors are integrated into the substrate and are far from the heating wire, the temperature difference in this system rapidly reaches its peak as wind speed increases and then decreases. By adjusting the R value, the curvature of this curve can be reduced. Therefore, a curve corresponding to the second mathematical theoretical basis can be formed. In summary, the output signal of the junction connecting the first and second temperature-sensitive resistive sensors is a voltage quantity formula.

[0067] eq.17

[0068] In the above formula, a1, a2, b1, and b2 are all positive numbers, and a2 is much larger than a1, and b2 is much larger than b1.

[0069] Based on the above analog circuit theory, such as Figure 1As shown, a MEMS chip for sensing heat-sensitive gas flow includes: a substrate, which is a single-crystal silicon wafer with a crystal orientation of 100; a central heating wire 101; a first temperature-sensitive resistive sensor 1021; a second temperature-sensitive resistive sensor 1022; a first BJT bipolar transistor assembly; a second BJT bipolar transistor assembly; and a thermal bridge 106. The first temperature-sensitive resistive sensor 1021 and the second temperature-sensitive resistive sensor 1022 are two sets of platinum wire thermal resistors with the same resistance and parameters. The central heating wire 101 is located at the central axis of symmetry on the thermal bridge 106. The bottom has an insulating cavity 105, and both ends of the insulating cavity 105 perpendicular to the arrangement direction of the central heating wire 101 are connected to a thermal bridge 106. The insulating cavity 105 is shaped like an inverted frustum and its exterior is a substrate. The first and second temperature-sensitive resistive sensors are connected in series to form a half-arm Wheatstone bridge and are located at equidistant positions at both ends of the central heating wire 101 and on the thermal bridge. The first and second BJT bipolar transistor combinations have the same structure and are located on the substrates on both sides of the insulating cavity 105 along the arrangement direction of the central heating wire 101. The first and second BJT bipolar transistor combinations are equidistant from the heating wire. The bipolar transistor assembly, a first PNP type BJT transistor assembly 1031, includes a first BJT transistor and a second BJT transistor. The first BJT transistor comprises N basic BJT transistor units of identical shape, size, and process technology, with their collectors and bases short-circuited and connected in parallel. The second BJT transistor comprises M basic BJT transistor units of identical shape, size, and process technology, with their collectors and bases short-circuited and connected in parallel. The emitters of the N basic BJT transistor units of the first BJT transistor are connected in parallel, and the emitters of the M basic BJT transistor units of the second BJT transistor are connected in parallel. The second BJT bipolar transistor... The second PNP type BJT bipolar transistor assembly 1032 includes a third BJT transistor and a fourth BJT transistor. The collectors and bases of the M basic BJT transistor units of the third BJT transistor with the same shape, size and process are short-circuited and connected in parallel. The collectors and bases of the N basic BJT transistor units of the fourth BJT transistor with the same shape, size and process are short-circuited and connected in parallel. The emitters of the M basic BJT transistor units of the third BJT transistor are connected in parallel. The emitters of the N basic BJT transistor units of the fourth BJT transistor are connected in parallel. N is greater than or equal to 2, and M is greater than or equal to 1.

[0070] It also includes an ambient temperature sensor 104 and a heating wire constant temperature difference control module. The ambient temperature sensor 104 is used to connect to the heating wire constant temperature difference control module. The center heating wire 101, the first temperature-sensitive resistor sensor 1021 and the second temperature-sensitive resistor sensor 1022 are made of platinum metal, and the thermal bridge 106 is made of silicon dioxide or silicon nitride.

[0071] In some embodiments, a linear compensation system for a thermally sensing gas flow sensor includes a MEMS chip terminal for the thermally sensing gas flow sensor, and further includes: a first loop, a first shunt circuit, a second loop, and a second shunt circuit; a first output terminal of the first loop is connected to the input terminal of a first BJT transistor, and a second output terminal of the first loop is connected to the input terminal of a second BJT transistor; a shunt terminal of the first loop is connected to the input terminal of the first shunt circuit, and the output terminal of the first shunt circuit is connected to the input terminal of a first temperature-sensitive resistive sensor 1021; a first output terminal of the second loop is connected to the input terminal of a third BJT transistor, and a second output terminal of the second loop is connected to the input terminal of a fourth BJT transistor; a shunt terminal of the second loop is connected to the input terminal of the second shunt circuit, and the output terminal of the second shunt circuit is connected to the input terminal of a second temperature-sensitive resistive sensor 1022.

[0072] This design is based on an analog integrated ASIC using CMOS technology, but it can also be based on a circuit board and discrete components when volume and signal quality requirements are not high. This linear compensation module includes a linear compensation module designed based on the mathematical theory mentioned in this invention, and a conventionally designed heating wire constant temperature difference compensation module. Figure 7As shown, a linear compensation system for a thermally sensing gas flow sensor includes a MEMS chip for the thermally sensing gas flow sensor, and further includes a first loop, a second loop, a first loop starter, and a second loop starter. The first and second loop starters respectively activate the first and second loops after the system is powered on. The first loop includes a first voltage-controlled current generator, a first voltage differencer, and a first load impedance. The first current output terminal of the first voltage-controlled current generator flows through the first load impedance and a first BJT transistor, and the second current output terminal of the first voltage-controlled current generator flows through a second BJT transistor. The sum of the voltages of the first load impedance and the first BJT transistor is connected to the first input terminal of the first voltage differencer, the voltage output terminal of the second BJT transistor is connected to the second input terminal of the first voltage differencer, and the output terminal of the first voltage differencer is connected to the control terminal of the first voltage-controlled current generator. The second loop includes a second voltage-controlled current generator... The system includes a second voltage differencer, a second load impedance, a second voltage-controlled current generator, a third BJT transistor, and a second load impedance and a fourth BJT transistor. The voltage output of the third BJT transistor is connected to the first input of the second voltage differencer, and the voltage outputs of the second load impedance and the fourth BJT transistor are connected to the second input of the second voltage differencer. The output of the second voltage differencer is connected to the control terminal of the second voltage-controlled current generator. The system also includes a first current amplifier and a second current amplifier. The output of the first voltage differencer is connected to the input of the first current amplifier, and the output of the first current amplifier is connected to the non-series terminal of the first temperature-sensitive resistor sensor 1021. The output of the second voltage differencer is connected to the input of the second current amplifier, and the output of the second current amplifier is connected to the non-series terminal of the second temperature-sensitive resistor sensor 1022.

[0073] In some embodiments, a linear compensation system for a thermally sensing gas flow sensor includes a MEMS chip for the thermally sensing gas flow sensor, and further includes: a first loop, a first replication circuit, a second loop, and a second replication circuit; a first output terminal of the first loop is connected to the input terminal of a first BJT transistor, and a second output terminal of the first loop is connected to the input terminal of a second BJT transistor; the first replication circuit replicates the current of the first BJT transistor or the second BJT transistor; the output terminal of the first replication circuit is connected to the input terminal of a first temperature-sensitive resistive sensor 1021; a first output terminal of the second loop is connected to the input terminal of a third BJT transistor, and a second output terminal of the second loop is connected to the input terminal of a fourth BJT transistor; the second replication circuit replicates the current of the third BJT transistor or the fourth BJT transistor; and the output terminal of the second replication circuit is connected to the input terminal of a second temperature-sensitive resistive sensor 1022.

[0074] like Figure 8 As shown, in some embodiments, a current-controlled enhanced linear compensation system for a thermally sensing gas flow sensor includes a MEMS chip for the thermally sensing gas flow sensor, and further includes a first loop, a second loop, a first loop starter, and a second loop starter. The first and second loop starters respectively activate the first and second loops when the system is powered on. The first loop includes a first stacked voltage-controlled current generator, a first voltage differencer, and a first load impedance. The first current output terminal of the first stacked voltage-controlled current generator flows through the first load impedance and a first BJT transistor, and the second current output terminal of the first stacked voltage-controlled current generator flows through a second BJT transistor. The sum of the voltages of the first load impedance and the first BJT transistor is connected to the first input terminal of the first voltage differencer, the voltage output terminal of the second BJT transistor is connected to the second input terminal of the first voltage differencer, and the output terminal of the first voltage differencer is connected to the control terminal of the first stacked voltage-controlled current generator. The second loop includes a second stacked voltage-controlled current generator. The system includes a voltage-controlled current generator, a second voltage differencer, and a second load impedance. The first current output of the second stacked voltage-controlled current generator flows through a third BJT transistor, and the second current output of the second voltage-controlled current generator flows through the second load impedance and a fourth BJT transistor. The voltage output of the third BJT transistor is connected to the first input of the second voltage differencer, and the sum of the voltages of the second load impedance and the fourth BJT transistor is connected to the second input of the second voltage differencer. The output of the second voltage differencer is connected to the control terminal of the second stacked voltage-controlled current generator. The system also includes a first current replication amplification circuit and a second current replication amplification circuit. The first current replication amplification circuit replicates the emitter current of the first BJT transistor, and the second current replication amplification circuit replicates the emitter current of the fourth BJT transistor. The outputs of the first and second current replication amplification circuits are respectively connected to the non-series terminals of a first temperature-sensitive resistive sensor 1021 and a second temperature-sensitive resistive sensor 1022.

[0075] like Figure 9As shown, in some embodiments, a discrete linear compensation system for a thermally sensing gas flow sensor includes a MEMS chip for the thermally sensing gas flow sensor, and further includes a first loop, a first replication circuit, a second loop, and a second replication circuit. The first loop includes a first voltage-controlled current generator, a first discrete voltage differencer, and a first load impedance. The first output terminal of the first voltage-controlled current generator is connected to the first load and a first BJT transistor, and the second output terminal of the first voltage-controlled current generator is connected to the input terminal of a second BJT transistor. The sum of the voltages of the first load impedance and the first BJT transistor is output to the first input terminal of the first discrete voltage differencer, the voltage output terminal of the second BJT transistor is connected to the second input terminal of the first discrete voltage differencer, and the output terminal of the first discrete voltage differencer is connected to the control terminal of the first voltage-controlled current generator. The first current replication circuit replicates the first BJT transistor. The emitter current of the BJT transistor; the output of the first replication circuit is connected to the input of the first temperature-sensitive resistive sensor 1021; the second loop includes a second voltage-controlled current generator, a second discrete voltage differencer, and a second load impedance; the first output of the second voltage-controlled current generator is connected to the third BJT transistor, and the second output of the second voltage-controlled current generator is connected to the second impedance and the fourth BJT transistor; the output voltage of the third BJT transistor is connected to the first input of the second discrete voltage differencer, the sum of the voltages of the second load impedance and the fourth BJT transistor is connected to the second input of the second discrete voltage differencer, and the output of the second discrete voltage differencer is connected to the control terminal of the second voltage-controlled current generator; the second current replication circuit replicates the emitter current of the fourth BJT transistor; the output of the second replication circuit is connected to the input of the second temperature-sensitive resistive sensor 1022.

[0076] like Figure 10As shown, in some embodiments, a discrete inverting current linear compensation system for a thermally sensing gas flow sensor includes a MEMS chip terminal for the thermally sensing gas flow sensor. A first loop includes: a first inverting voltage-controlled current generator, a first load impedance, and a first voltage differencer; a second loop includes: a second inverting voltage-controlled current generator, a second load impedance, and a second voltage differencer; and this circuit further includes: a first startup module and a second startup module; when the system is powered on, the first startup module starts the first loop and then automatically disconnects, and the second startup module starts the second loop and then automatically disconnects; the first output terminal of the first inverting voltage-controlled current generator flows through the first load impedance and the emitter of the first BJT transistor; the second output terminal of the first inverting voltage-controlled current generator flows through the emitter of the second BJT transistor; the current at the first output terminal of the second inverting voltage-controlled current generator flows through the emitter of the third BJT transistor; the second inverting voltage-controlled current generator... The current at the second output terminal flows through the second load impedance and the emitter of the fourth BJT transistor; the first input terminal of the first voltage differencer is connected to the first load impedance and the output voltage of the first BJT transistor, and the second input terminal is connected to the output voltage of the second BJT transistor; the output terminal of the first voltage differencer is connected to the control terminal of the first inverting voltage controlled current generator; the first input terminal of the second voltage differencer is connected to the output voltage of the third BJT transistor, and the second input terminal is connected to the second impedance and the output voltage of the fourth BJT transistor; the output terminal of the second voltage differencer is connected to the control terminal of the second inverting voltage controlled current generator; the first current replication circuit replicates the emitter current of the first BJT transistor, and the second current replication circuit replicates the emitter current of the fourth BJT transistor; the output terminals of the first current replication circuit and the second current replication circuit are respectively connected to the non-series terminals of the first temperature-sensitive resistive sensor 1021 and the second temperature-sensitive resistive sensor 1022.

[0077] like Figure 11As shown, in some embodiments, a simplified discrete linear compensation system for a thermally sensing gas flow sensor includes a MEMS chip terminal for the thermally sensing gas flow sensor. The first loop includes: a first current bias resistor, a second current bias resistor, a first load impedance, and a first voltage differencer; the second loop includes: a third current bias resistor, a fourth current bias resistor, a second load impedance, and a second voltage differencer; and this circuit further includes: a first startup module and a second startup module; when the system is powered on, the first startup module starts the first loop and then automatically disconnects, and the second startup module starts the second loop and then automatically disconnects; the output of the first current bias resistor flows through the first load impedance and the emitter of the first BJT transistor; the output of the second current bias resistor flows through the emitter of the second BJT transistor; the output current of the third bias resistor flows through the emitter of the third BJT transistor; and the output current of the fourth bias resistor flows through the fourth BJT transistor. The emitter of the transistor; the first input terminal of the first voltage differencer is connected to the first load impedance and the output voltage of the first BJT transistor, and the second input terminal is connected to the output voltage of the second BJT transistor; the output terminal of the first voltage differencer is connected to the non-series terminals of the first current bias resistor and the second bias resistor; the first input terminal of the second voltage differencer is connected to the output voltage of the third BJT transistor, and the second input terminal is connected to the second impedance and the output voltage of the fourth BJT transistor; the output terminal of the second voltage differencer is connected to the non-series terminals of the third current bias resistor and the fourth current bias resistor; the output terminal of the first voltage differencer is connected to the first current amplification module; the output terminal of the second voltage differencer is connected to the second current amplification module; the output terminals of the first current amplification module and the second current amplification module are respectively connected to the non-series terminals of the first temperature-sensitive resistive sensor 1021 and the second temperature-sensitive resistive sensor 1022.

[0078] In some embodiments, the heating wire constant temperature difference control module includes: a first voltage divider, a second voltage divider, and a third voltage differencer; the first voltage divider includes a first external resistor Ra, one end of which is connected in series with an ambient temperature sensor 104; the second voltage divider includes a second external resistor Rb, one end of which is connected in series with a central heating wire 101; the other ends of the first external resistor Ra and the second external resistor Rb are connected together; the other ends of the ambient temperature sensor 104 and the central heating wire 101 are grounded; the connection between the first external resistor Ra and the ambient temperature sensor 104 is connected to the first input terminal of the third voltage differencer; the connection between the second external resistor Rb and the central heating wire 101 is connected to the second input terminal of the third voltage differencer; and the output terminal of the third voltage differencer is connected to the connection between the first external resistor Ra and the second external resistor Rb.

[0079] This invention requires the MEMS chip and ASIC linear compensation circuits to work together. The system needs the output linearity compensation circuit and the heating wire constant temperature difference compensation module mentioned above to operate in conjunction. Upon system power-up, a self-starting current reference source activates to provide stable operating current for other modules, such as... Figure 2 As shown, the first and second loops will not operate immediately due to their self-stabilizing characteristics. At this time, the starters of the first and second loops activate their corresponding first and second loops by detecting the voltage and inverting voltage internal modules, and then automatically shut down. The first and second loops respectively generate two stable proportional currents, which are input to the first PNP BJT bipolar transistor combination and the second PNP BJT bipolar transistor combination. The two loops operate on the same principle. Taking the first loop and the first PNP BJT bipolar transistor combination as an example, the submodule of the first voltage-controlled current generator in the first loop generates two currents I1:I2=1:N. I1 flows into the first BJT transistor in the first PNP BJT transistor combination, and I2 flows into the second BJT transistor in the first PNP BJT transistor group. At this time, currents I1 and I2 generate two voltages V1 and V2, which are input to the first voltage differencer and output as a voltage difference. This voltage difference is then input to the first voltage-controlled current generator, thus forming a self-stabilizing loop. The significance of designing this circuit is: 1. To reduce the impact of power supply voltage and circuit self-heating, generating a stable proportional current to improve the temperature sensing accuracy of the transistor group. 2. To adjust the voltage of each load BJT transistor to the required value. This linear compensation circuit connects the first and second PNP type BJT bipolar transistor combinations on the MEMS chip side, generating a temperature-positive current as shown in eq. 16, and finally outputting it through current replication and amplification. The linear compensation circuit of this invention also contains a constant temperature difference control current based on a common heating wire structure, which functions to reduce the impact of room temperature changes on the sensor output. Its sub-modules are: ambient temperature sensor, second voltage divider, and third voltage differencer. The working principle is that the ambient temperature sensor and the ambient temperature sensor 104 on the MEMS chip side form the first branch, and the second voltage divider and the center heating wire on the MEMS chip side form the second branch. The first branch, the second branch, and the third voltage differencer form the third loop. The first branch output voltage, V1, is related to the resistance of the ambient temperature sensor 104. The second branch output voltage, V2, is related to the resistance of the heating wire. These two branch output voltages are fed to the third voltage differencer and output V3. When the circuit starts, V1 and V2 are not equal. The third voltage differencer continuously increases the voltage and re-inputs it to the first and second branches. During this time, the heating wire continues to heat up, thus increasing its resistance. When V1 = V2, the third voltage differencer stops working, and the heating wire temperature reaches a stable value. When the ambient temperature changes or the heating wire temperature changes, this loop balance is broken, and the third voltage differencer starts working and drives the circuit to another equilibrium point.

[0080] Based on the above modules, the central heating wire at the MEMS chip end, the first temperature-sensitive resistive sensor 1021 on the thermal bridge, the second temperature-sensitive resistive sensor 1021, the first BJT bipolar transistor combination, and the second BJT bipolar transistor combination can sense the gas flow rate and compensate for nonlinearity at the ideal voltage and current operating point. The system output voltage is shown in eq.17. Figure 3 and Figure 4 As shown, the MEMS chip design of this sensor uses the extension line of the heating wire as the axis of symmetry, with symmetrical geometric features at both ends. The temperature difference / current module in the linear compensation circuit also features the same design. Therefore, it can meet the requirements for bidirectional gas flow measurement.

[0081] This invention proposes a method for computational compensation using analog circuits. A specially designed analog circuit connects quantities related to a gas flow sensor, such as temperature difference, heat exchange, resistance, and current, directly implementing the compensation algorithm at the analog circuit level to compensate for the linearity of the output voltage. Compared to traditional compensation algorithms based on digital computing systems, this method significantly simplifies the circuitry and can be applied to mobile devices and other applications with high requirements for size, power consumption, and accuracy.

[0082] Example 1

[0083] This embodiment includes a MEMS chip terminal, such as... Figure 5 and Figure 6 As shown, the accompanying compensation circuit is designed as an ASIC integrated circuit based on CMOS technology. The system diagram for this embodiment is shown below. Figure 7 .

[0084] The sensor output linearity compensation circuit is based on a novel design proposed in this invention. This output linearity compensation system includes a first reference current source, a first loop, a second loop, a first startup module, a second startup module, a first current amplifier, and a second current amplifier. The first loop includes a first voltage-controlled current generator, a first voltage differencer, and a first load impedance. The second loop includes a second voltage-controlled current generator, a second voltage differencer, and a second load impedance. In this embodiment, the components of the first reference current source are: P-type MOSFETs M9, M10, and M13; N-type MOSFETs M11 and M12; and resistor R3. The components of the first voltage-controlled current generator are: P-type MOSFETs M1 and M2. The components of the second voltage-controlled current generator are: P-type MOSFETs M5 and M6. The first voltage difference finder includes the following components: P-type MOSFETs M14 and M15, and N-type MOSFETs M18, M19, and M22; the second voltage difference finder includes the following components: P-type MOSFETs M17 and M16, and N-type MOSFETs M20, M21, and M23; the first load impedance is N-type MOSFET M7; the second load impedance is N-type MOSFET M8; the first startup module includes the following components: P-type MOSFETs M24 and M27, and N-type MOSFETs M28, M25, and M26; the second startup module includes the following components: P-type MOSFETs M29 and M32, and N-type MOSFETs M30, M31, and M33; the first current amplifier is P-type MOSFET M3; the second current amplifier is P-type MOSFET M6; the reference current source can generate a current independent of the power supply voltage to achieve constant current through a loop structure that replicates the two current mirror circuits. The first and second loops operate on the same principle, as do the first and second startup modules, the first and second load impedances, and the first and second current amplifiers. An example is the system consisting of the first loop, the first startup module, the first load impedance, and the first current amplifier. When the system is powered on, P-type MOSFET M27 and N-type MOSFET M26 form an output detection circuit; when the current in the first current mirror is close to 0A, the output is also approximately 0V. P-type MOSFET M24 and N-type MOSFET M25 form a first voltage inverter; when its input is approximately 0V, the output is approximately 5V. The N-type MOSFET M28 serves as the first start-up driver. When the output of the first voltage inverter is approximately 5V, the driver M28 generates a high current and outputs it to the loop mentioned above, which contains P-type MOSFETs M1 and M2, to start its operation. After the first voltage-controlled current generator starts, the voltage input to M28 from the first starter is approximately 0V, at which point the starter disconnects.When the first voltage-controlled current generator operates, the ratio of the current I1 from the first BJT transistor Q1 to the output current I2 from the second BJT transistor Q2 is 1:8. I1 flows through the first load impedance NMOS transistor M7 and the first BJT transistor Q1 to generate voltage V1, and I2 flows through the second BJT transistor Q2 to generate voltage V2. V1 and V2 are input to the first voltage differencer and generate a voltage difference V5. Voltage V5 is re-inputted to the gates of P-type MOSFETs M1 and M2 and regenerates a pair of proportional currents I1 and I2. When V1 = V2, since V1 - V2 = 0, this loop reaches a steady state, and the following relationship exists at this time.

[0085]

[0086] In the above formula, V T R is the PN junction thermal voltage, I1 and I2 are the currents of the first BJT transistor Q1 and the second BJT transistor Q2, respectively, Is1 and Is2 are the inverting saturation currents of the two BJT transistors, and R is the inverting saturation current of the two BJT transistors. M7 This is the equivalent impedance of the first load impedance M7.

[0087] Transforming the above equation, we get

[0088]

[0089] Among them, V T This represents the thermal current of the BJT transistor.

[0090] Based on the above formula, taking the MEMS chip-side embodiment of this invention as an example, the emitter areas of the two BJT transistors are in a 1:8 ratio, therefore I1:I2 = 1:8. Furthermore, BJT transistors Q1 and Q2 are at the same temperature, V... T =kT / q, we can get

[0091]

[0092] Where k and q are constants, and R M7 T is the equivalent resistance of the MOSFET impedance. 1,2 Let Q1 and Q2 be the temperatures at the BJT transistors. The circuit generates a temperature-dependent current I1. In a circuit composed of BJT transistors Q3 and Q4, based on the same principle and with I3:I4 = 8:1, the current flowing through the fourth BJT transistor Q4 is...

[0093]

[0094] Where k and q are constants, and R M8 T is the equivalent resistance of the MOSFET impedance. 3,4The values ​​represent the temperatures at BJT transistors Q3 and Q4. I1 and I4 are replicated by current amplifiers PMOS transistors M3 and M4 with the same current and output to the first and second temperature-sensitive resistive sensors 1022 and 1021 on the MEMS chip.

[0095] This ASIC also integrates a heating wire constant temperature difference compensation circuit, including a third differential voltage amplifier, a first common-source voltage amplifier, a first common-drain voltage amplifier, a phase compensation capacitor C1, an external resistor Ra, and an external resistor Rb. P-type MOSFETs M34 and M35, N-type MOSFETs M36, M37, and M38 constitute the third differential voltage amplifier. P-type MOSFET M39 and N-type MOSFET M40 constitute the first common-source voltage amplifier. N-type MOSFETs M44 and M42 constitute the first common-drain voltage amplifier. When the circuit starts operating, the third differential voltage amplifier outputs a relatively low initial voltage, with different voltage division ratios between branch Ra and the ambient temperature sensing resistor 104, and between branch Rb and the heating wire 101. The voltage outputs from these two paths are fed to a third differential voltage amplifier for voltage difference calculation. This voltage difference is then amplified by a first common-source voltage amplifier to sufficiently drive the circuit. The output of the first common-source voltage amplifier is then passed through a first common-drain amplifier to improve its load-carrying capacity. Finally, the output of the common-drain voltage amplifier is input again into a resistive circuit consisting of resistors Ra and Rb, an ambient temperature sensor, and a heating wire. Because the central heating wire is located on a thermally insulating bridge, this loop ultimately achieves a balanced output voltage state between the two branches, thus achieving constant temperature. This constant temperature difference module can reduce output drift caused by changes in room temperature.

[0096] The current difference between the current I1 of BJT transistor Q1 and the current I4 of BJT transistor Q4 mentioned above is:

[0097]

[0098] T 1,2 T represents the temperatures at points Q1 and Q2 of the BJT tube. 3,4 The temperatures at points Q3 and Q4 of the BJT tube are due to R. M7 =R M8 With the same settings and the same two equivalent resistances, the above equation can be combined into:

[0099]

[0100] These two currents flow into one end of the first and second temperature-sensitive resistive sensors 1022 and 1021 on the MEMS chip, respectively. Using the superposition theorem, they can be considered as current I. diffThe current flows from one end into a Wheatstone bridge formed by the first and second temperature-sensitive resistive sensors 1022 and 1021. The output voltage of this bridge is...

[0101]

[0102] ΔT1 is the temperature difference between one thermistor and the reference temperature after being heated by the heating wire, and ΔT2 is the temperature difference between the other thermistor and the reference temperature after being heated by the heating wire. Assuming R is the resistance value when the temperature is between ΔT1 and ΔT2, the above formula can be simplified to...

[0103]

[0104] Output voltage is

[0105]

[0106] Example 2

[0107] This embodiment includes a MEMS chip terminal, such as... Figure 5 and Figure 6 As shown, the accompanying compensation circuit is designed as an ASIC integrated circuit based on CMOS technology. The system diagram for this embodiment is shown below. Figure 8 .

[0108] The sensor output linearity compensation circuit is based on a novel design proposed in this invention. This output linearity compensation system includes a second reference current source, a third loop, a fourth loop, a third startup module, a fourth startup module, a third current amplifier, and a fourth current amplifier.The third loop includes: a first stacked voltage-controlled current generator, a fourth voltage differencer, and a third load impedance; the fourth loop includes: a second stacked voltage-controlled current generator, a fifth voltage differencer, and a fourth load impedance; wherein the second reference current source includes components: P-type MOSFETs M15, M16, M17, M18, and N-type MOSFETs M19, M21, M20, M22, M23, M24, and resistor R3; the first stacked voltage-controlled current generator includes components: P-type MOSFETs M3, M4, M7, M8; the second stacked voltage-controlled current generator includes components: P-type MOSFETs M5, M6, M9, M10; the fourth voltage differencer includes components: P-type MOSFETs M25, M26, and N-type MOSFETs M29, M30, M33; the fifth voltage differencer includes components... The third starting module includes P-type MOSFETs M27 and M28, and N-type MOSFETs M31, M32, and M34; the fourth starting module includes P-type MOSFET M36, and N-type MOSFETs M35, M39, and M40; the fifth starting module includes P-type MOSFET M38, and N-type MOSFETs M42, M43, and M44; the sixth current amplifier includes P-type MOSFETs M11 and M12; the seventh current amplifier includes P-type MOSFETs M13 and M14; the third and fourth loops operate on the same principle, and the third starting module is... The fourth startup module operates on the same principle, as do the third and fourth current amplifiers. The following explanation uses a system consisting of the third loop, the third startup module, and the third current amplifier as an example. P-type MOSFETs M15, M16, M17, and M18 form a second-stage current mirror, and N-type MOSFETs M19, M21, M20, and M22 form another second-stage current mirror. These two mirrors replicate each other's current to form a self-sustaining current loop. N-type MOSFETs M23 and M24 act as starters for this loop, generating an initial voltage to start the two current mirrors when the system is connected to power. Resistor R3 is... NMOS transistor M22 provides a bias voltage to ensure that the output of this constant current source is not zero; the function of the fourth and fifth voltage differencers is to output the voltage difference between the two paths, V3=V1-V2 and V6=V4-V5; P-type MOSFETs M25 and M26 are connected to the second reference current source to form a pair of constant current sources to ensure that the connected components are in working condition. The two currents flow into N-type MOSFETs M29 and M30, which are controlled by the input voltages V1 and V2. Due to the voltage effect of V1 and V2, the two generate currents and merge into N-type MOSFET M33, which converts the current into voltage V3, which is the voltage difference between V1 and V2; N-type MOSFETs M1 and M2 are controlled by bias voltage source 2 and work as resistors in the linear region; when the system is powered on, the third startup module starts the third loop and then shuts down automatically.This starter transitions the third loop from its self-stabilized output state to the operating state by detecting the loop output and outputting the voltage. The gate of NMOS transistor M35 is connected to the gate of the PMOS transistor in the current mirror. After the system is powered on, the current mirror does not start due to its self-holding function, and the gate voltage of this PMOS transistor is close to the power supply voltage. This voltage acts on the gate of NMOS transistor M35. Since the start-up voltages of NMOS and PMOS are opposite, NMOS transistor M35 is started and generates current flowing through PMOS transistor M36, which is a self-biased MOSFET load. When the current generated by NMOS transistor M35 flows through it, a voltage is generated at the output terminal. This output voltage acts on NMOS transistors M39 and M40, generating two currents. These two currents flow into the first and second PNP BJT transistors Q1 and Q2, enabling the loop to start and achieve self-sustaining operation. When the loop generates an output, PMOS transistors M7, M8, M3, and M4 turn on, and their gate voltages automatically decrease. This voltage simultaneously acts on the gate of NMOS transistor M35, which turns off due to the decrease in gate voltage. The startup circuit stops outputting startup current to the loop, and the startup process is complete. The ratio of current I1 in PMOS transistors M7 and M3 to current I2 in PMOS transistors M8 and M4 is 1:8. Current I1 flows through the third load impedance M1 and the first BJT transistor Q1 to generate voltage V1, and current I2 flows through the second BJT transistor Q2 to generate voltage V2. At this time, voltages V1 and V2 are different, and the voltages V1 and V2 act on the fourth voltage differencer; its output difference V3 acts on the gates of PMOS transistors M3, M4, M7, and M8 to control the magnitude of their generated currents. Finally, when V1 = V2, V1 - V2 = 0, and the loop reaches equilibrium. At this time, two conditions are satisfied: V1 = V2 and I1:I2 = 1:8. Therefore, the following equation can be derived.

[0109]

[0110] Where I S1 I S2 V represents the reverse saturation current of the two BJT transistors. T R is the thermal voltage of the PN junction of the two BJT transistors. M1 Let I be the equivalent resistance of the MOSFET as the load impedance. When both BJT transistors operate at the same temperature, and I... S1 I S2 It is temperature-dependent. Therefore, the above equation can be transformed into:

[0111]

[0112] The two BJT tubes are at the same temperature, V T =k*T / q, we can get

[0113]

[0114] The above equation shows that the current generated in this loop is positively correlated with temperature. Based on the same principle, in the fourth loop, the ratio of I3:I4 between the third BJT transistor Q3 and the fourth BJT transistor Q4 is 8:1. Therefore, the current flowing through BJT transistor Q4 is...

[0115]

[0116] I1 and I4 are replicated by P-type MOSFETs M11, M12 and M13, M14 respectively and output to the first and second temperature-sensitive resistive sensors 1022 and 1021.

[0117] The heating wire constant temperature difference compensation module includes a sixth voltage difference calculator, a first common-source voltage amplifier, a first common-drain voltage amplifier, a phase compensation capacitor C1, a first external resistor Ra, and a second external resistor Rb. P-type MOSFETs M37 and M41, and N-type MOSFETs M46, M47, and M48 constitute the sixth voltage difference calculator. P-type MOSFET M45 and N-type MOSFET M49 constitute the second common-source voltage amplifier. N-type MOSFETs M52 and M51 constitute the second common-drain voltage amplifier. Capacitor C1 is a phase compensation capacitor, which prevents output instability caused by excessive input voltage changes. When the circuit starts running, the sixth voltage difference calculator outputs an initial voltage V9, which is then output through the second common-source voltage amplifier and the second common-drain voltage amplifier to the branch consisting of Ra and the ambient temperature sensing resistor 104, and the branch consisting of Rb and the heating wire 101. Because the input voltages are the same but the resistance ratios are different, these two branches have different output voltages V7 and V8. V7 and V8 are input to the sixth differential voltage amplifier for voltage difference calculation to update V9, and then input again to the two resistive branches through the second common-source voltage amplifier and the second common-drain voltage amplifier. During this process, the central heating wire 101 self-heats and changes its own resistance due to heat. Finally, when V7 = V8, this loop reaches equilibrium, and the heating wire reaches a constant temperature.

[0118] Under the control of this constant temperature difference controller, the temperature difference between the central heating wire 101 and the ambient temperature remains constant at the same wind speed. Simultaneously, the temperature difference at the locations of the first and second PNP BJT bipolar transistor combinations 1031 and 1032 can also be approximated as constant at the same wind speed. Under this environment, the temperature difference between the first and second PNP BJT bipolar transistor combinations 1032 and 1031...

[0119] The generated current difference is

[0120]

[0121] I 1031 and I 1032The current flows into one end of the first and second temperature-sensitive resistive sensors 1021 and 1022, respectively. Using the current superposition theorem, this can be considered as the current Idiff flowing into the Wheatstone bridge formed by the first and second temperature-sensitive resistive sensors 1021 and 1022 from one end. The output voltage of this bridge is...

[0122]

[0123] If we take the midpoint of the two temperature differences, the above equation can be approximately simplified to:

[0124]

[0125] Output voltage is

[0126]

[0127] Example 3

[0128] This embodiment includes a MEMS chip terminal, such as... Figure 5 and Figure 6 As shown, the accompanying compensation circuit is designed as an ASIC integrated circuit based on CMOS technology. The system diagram for this embodiment is shown below. Figure 9 .like Figure 9As shown, the output linearity compensation module includes a fifth loop, a sixth loop, a fifth startup module, a sixth startup module, a fifth current amplifier, and a sixth current amplifier. The fifth loop includes: a first operational amplifier U1, a fifth voltage-controlled current generator, and a first PCB resistor 1; the sixth loop includes: a second operational amplifier U2, a sixth voltage-controlled current generator, and a second PCB resistor 2; the discrete operational amplifiers U1 and U2 each contain a reference current source, a differential voltage amplifier, a common-source voltage amplifier, and a common-drain voltage amplifier. P-type MOSFETs M1 and M2 serve as the fifth voltage-controlled current generator, and P-type MOSFETs M5 and M6 serve as the sixth voltage-controlled current generator. P-type MOSFETs M11 and M7, N-type MOSFETs M9 and M13, and resistor R1 constitute the fifth startup module. P-type MOSFETs M8 and M12, N-type MOSFETs M10 and M14, and resistor R2 constitute the sixth startup module. The fifth and sixth loops operate on the same principle, as do the fifth and sixth startup modules. The following example uses the fifth loop, fifth startup module, and fifth current amplifier. When the system is powered on, there is no current in the fifth loop, and due to the loop's self-holding effect, this loop will not start automatically. In the fifth startup module, the P-type MOSFET M11 replicates the current flowing through Q1. Since the current is approximately zero, the voltage across resistor R1 is also approximately 0V. This voltage flows into the inverter formed by PMOS transistors M7 and M9, and the output is approximately the system power supply voltage. This inverter output voltage is sent to NMOS transistor M13, which generates a voltage and applies it to the gates of PMOS transistors M1 and M2, thus starting the fifth loop. Subsequently, a high voltage is also output across resistor R1. This voltage is converted to near 0V by the inverter and ultimately acts on NMOS transistor M13 to shut down the startup circuit output.

[0129] PMOS transistors M1 and M2 maintain a current ratio of 1:8 between the first BJT transistor Q1 (I1) and the second BJT transistor Q2 (I2). I1 flows through resistor 1 on the first PCB and BJT transistor Q1, generating voltage V1. I2 flows through BJT transistor Q2, generating voltage V2. V1 and V2 flow through the first operational amplifier U1, generating a voltage difference V3, which is then applied to the gates of PMOS transistors M1 and M2, thus updating the currents I1 and I2. When V1 = V2, V1 - V2 = 0, and the loop reaches a steady state. At this point, based on the relationship V1 = V2 and I1:I2 = 8, the following equation can be written:

[0130]

[0131] Where I S1 I S2 V represents the inverting saturation current of the two BJT transistors, the first and second. T R is the PN junction thermal voltage of Q1 and Q2.PCB1 This refers to the resistance value on the PCB. Because the first and second BJT transistors Q1 and Q2 operate at the same temperature, and I... S1 I S2 It is temperature-dependent. Therefore, the above equation can be transformed into:

[0132]

[0133] Based on the above formula, in this example, I1:I2=1:8, V T =k*T / q, we can get

[0134]

[0135] The above equation shows that the current generated in this loop is positively correlated with temperature. Based on the same principle, the currents flowing through BJT transistors Q3 and Q4 in the second loop are I3:I4 = 8:1, and the current flowing through the fourth BJT transistor Q4 is...

[0136]

[0137] I1 and I4 are replicated by the current-replicating amplifier transistors PMOS transistors M3 and M4, respectively, and output to the first and second temperature-sensitive resistive sensors 1021 and 1022.

[0138] This system also includes a constant temperature difference compensation module. Operational amplifier U3 outputs an initial voltage V9, which acts on the first branch containing the first external resistor Ra and the ambient temperature sensing resistor 104, and the second branch containing the external resistor Rb and the sensor's central heating wire 101. Due to the different resistance ratios, the first and second branches output unequal voltages V7 and V8 under the same input voltage V9. The sensor's central heating wire is located on a thermal bridge, and its resistance changes due to heat as it heats up, thus changing the output voltage V8 of the second branch. V7 and V8 are input to operational amplifier U3 again, generating a new output voltage V9. When V7 = V8, since V7 - V8 = 0, the system reaches a stable state. When the ambient temperature changes, the output voltage of the first branch changes, and this loop again adjusts to achieve the state of V7 = V8, thereby achieving the purpose of a constant temperature difference between the ambient temperature and the heating wire temperature.

[0139] Under this constant temperature difference environment, the two sets of first and fourth BJT transistors generate a current difference of...

[0140]

[0141] I 1031 and I 1032The current flows into one end of the first and second temperature-sensitive resistive sensors 1021 and 1022, respectively. Using the current superposition theorem, this can be considered as the current Idiff flowing into the Wheatstone bridge formed by the first and second temperature-sensitive resistive sensors 1021 and 1022 from one end. The output voltage of this bridge is...

[0142]

[0143] If we take the midpoint of the two temperature differences, the above equation can be approximately simplified to:

[0144]

[0145] Output voltage is

[0146]

[0147] Example 4

[0148] The inventors propose another PCB-based embodiment. Unlike embodiment three, this design is based on an N-type MOSFET. This embodiment includes a MEMS chip terminal, such as... Figure 5 and Figure 6 As shown, the accompanying compensation circuit is designed based on discrete components and a PCB. A system diagram for this embodiment can be found here. Figure 10 .like Figure 10The PCB-side sensor output linearity compensation circuit includes: a seventh loop, an eighth loop, a seventh start-up module, an eighth start-up module, a seventh current amplifier, and an eighth current amplifier; the seventh loop includes: a first inverting voltage-controlled current generator, a tenth voltage differencer, and a seventh load impedance; the eighth loop includes: a second inverting voltage-controlled current generator, an eleventh voltage differencer, and an eighth load impedance; the first inverting voltage-controlled current generator includes N-type MOSFETs: M1 and M2; the second inverting voltage-controlled current generator includes N-type MOSFETs: M3 and M4; the first operational amplifier U1 serves as the tenth voltage differencer; the second operational amplifier U2 serves as the eleventh voltage differencer; the seventh... The load is resistor 1 on the PCB; the eighth load is resistor 2 on the PCB; the seventh startup module includes components: N-type MOSFET M7 and resistor R11; the eighth startup module includes components: N-type MOSFET M8 and resistor R12; the seventh current amplifier is N-type MOSFET M5; the eighth current amplifier is N-type MOSFET M6; the seventh and eighth loops operate on the same principle, as do the seventh and eighth startup modules and the seventh and eighth current amplifiers. The following explanation uses a system consisting of the seventh loop, the seventh startup module, and the seventh current amplifier as an example. When the system is powered on, the inverting voltage-controlled current generator in the loop structure has no current output. Therefore, the gate voltage of PMOS transistor M1 is approximately 0V, and PMOS transistor M7 is in open-circuit mode with a current close to 0A. At this time, the voltage difference across resistor R11 reaches its maximum, and current flows from resistor R11 into NMOS transistor M7, causing NMOS transistor M7 to start working and generate a gate-drain voltage. This voltage acts on the gates of PMOS transistors M1 and M2, causing them to generate current, which is maintained by operational amplifier U1. Simultaneously, the loop formed by PMOS transistors M1 and M2 and operational amplifier U1 begins to self-sustain and operate. The gate voltage of PMOS transistor M1 gradually increases and acts on resistor R11. The voltage difference across resistor R11 gradually decreases, resulting in a decrease in current and the shutdown of NMOS transistor M7. At this point, the startup module shuts down, and the first inverting voltage-controlled current generator begins to operate. The current I1 flowing through PMOS transistor M1 and the current I2 flowing through PMOS transistor M2 are maintained at a ratio of 1:8 under the first inverting voltage-controlled current generator. Simultaneously, I1 flows through resistor 1 on the first PCB and the first BJT transistor to generate voltage V1, and I2 flows through the second BJT transistor to generate voltage V2. V1 and V2 flow into operational amplifier U1, whose output is a voltage difference V3, which again acts on the gates of PMOS transistors M1 and M2, generating new I1 and I2. When V1 = V2, V1 - V2 = 0, bringing the loop to equilibrium. When V1 = V2, V1 - V2 = 0, this loop reaches a stable state. At this time, based on the relationship V1 = V2 and I1:I2 = 8, the following equation can be written.

[0149]

[0150] Where I S1 I S2 V represents the anti-phase saturation currents of two Q1 and Q2. T Let IS1 and IS2 be the PN junction thermal voltages of the two BJT transistors Q1 and Q2. Since the first and second BJT transistors Q1 and Q2 operate at the same temperature, and IS1 and IS2 are temperature-dependent, the above equation can be transformed into:

[0151]

[0152] Based on the above formula, and in this embodiment, I1:I2=1:8, V T =k*T / q, we can get

[0153]

[0154] The above equation shows that the current generated in this loop is positively correlated with temperature. Based on the same principle, and given that the ratio of currents I3 to I4 in Q3 and Q4 is 8:1, the current in I4 is...

[0155]

[0156] I1 and I4 are respectively output as current to the first and second temperature-sensitive resistive sensors.

[0157] This compensation module also includes a constant temperature difference compensation module for the heating wire based on a common design structure. This module maintains a constant temperature difference between the room temperature and the heating wire temperature to ensure that the output voltage of the measured wind speed is unaffected by the ambient temperature. After the circuit starts, operational amplifier U3 outputs an initial voltage V7, which acts on the first branch containing the first external resistor Ra and the ambient temperature sensor 104, and the second branch containing the first external resistor Rb and the sensor's central heating wire 101. Due to the different resistance ratios, the first and second branches output unequal voltages V5 and V6 under the same input voltage V7. The sensor's central heating wire, located on the thermal bridge, self-heats and changes its resistance due to heat, thus changing the output voltage V6 of the second branch. V5 and V6 are then input to operational amplifier U3 again, generating a new output voltage V7. When V5 = V6, since V5 - V6 = 0, the system reaches a stable state. When the ambient temperature changes, the output voltage of the first branch changes, and this loop adjusts itself to reach the state of V5=V6 again. This principle is used to achieve the purpose of a constant temperature difference between the ambient temperature and the heating wire temperature.

[0158] Under this constant temperature difference environment, the current difference generated by BJT transistor Q1 and BJT transistor Q4 is:

[0159]

[0160] I 1031 and I1032 The current flows into one end of the first and second temperature-sensitive resistive sensors on the MEMS chip, respectively. Using the current superposition theorem, this can be considered as the current Idiff flowing into a Wheatstone bridge formed by the first and second temperature-sensitive resistive sensors. The output voltage of this bridge is...

[0161]

[0162] If we take the midpoint of the two temperature differences, the above equation can be approximately simplified to:

[0163]

[0164] Output voltage is

[0165]

[0166] Example 5

[0167] The inventors propose another PCB-based embodiment. Unlike embodiments three and four, the compensation circuit in this design is built using bias resistors. This embodiment includes a MEMS chip such as... Figure 5 and Figure 6 As shown, the accompanying compensation circuit is designed based on discrete components and a PCB. A system diagram for this embodiment can be found here. Figure 11 This is a simplified current-free mirror implementation based on PCB and discrete components.

[0168] This output linearity compensation module includes: a ninth loop, a tenth loop, a ninth loop starter, a tenth loop starter, a ninth current amplifier, and a tenth current amplifier; the ninth loop includes: a bias resistor R2, a bias resistor R3, and a ninth load impedance R1, and the ninth loop starter includes a startup capacitor C1; the tenth loop includes components: a bias resistor R5, a bias resistor R6, and a tenth load impedance R4, and the tenth loop starter includes a startup capacitor C2; where R2 and R3 form a ninth voltage-controlled current generator, and R5 and R6 form a tenth voltage-controlled current generator. The first operational amplifier U1 is a thirteenth voltage difference module, and the second operational amplifier U2 is a fourteenth voltage difference module. R7, R9, and the NPN BJT transistor Q5 form a ninth current amplification module, and R8, R10, and the NPN BJT transistor Q6 form a tenth current amplification module. The current output terminal of the bias resistor R2 flows through the resistor R1 on the PCB and the first BJT transistor; the current output terminal of the bias resistor R3 flows through the second BJT transistor; the current output terminal of the bias resistor R5 flows through the resistor R4 on the PCB and the fourth BJT transistor; the current output terminal of the bias resistor R6 flows through the third BJT transistor; the voltage output terminals of the ninth load impedance and the first BJT transistor are connected to the first input terminal of the thirteenth voltage difference amplifier, the voltage output terminal of the second BJT transistor is connected to the second input terminal of the thirteenth voltage difference amplifier, and the output terminal of the thirteenth voltage difference amplifier is connected to the non-series connection end of the bias resistors R2 and R3; the output terminal of the thirteenth difference amplifier is connected to the input terminal of the ninth current amplification module, and the output terminal of the ninth current amplification module is connected to the non-series connection end of the first temperature-sensitive resistor type sensor 1021; the principles of the ninth loop and the tenth loop are the same, and the principles of the ninth current amplifier and the tenth current amplifier are the same. The ninth loop and the ninth current amplification module are used as examples for illustration. When the system is powered on, the loop will not start due to the self-holding characteristic. At this time, the capacitor C1 conducts due to the sudden change in the applied voltage. At this time, a voltage is applied to the first branch of R2, R1, Q1 and the second branch of R3, Q2, and two currents I1 and I2 are generated. When the first branch and the second branch start, the voltage change rate across C1 decreases, and C1 stops conducting. Due to the resistor voltage division principle, voltages V1 and V2 are generated in the first branch and the second branch and input to the operational amplifier U1. The output of the operational amplifier U1 is the difference voltage between V1 and V2, and it is re-input to the first branch and the second branch to generate a new round of voltage output. Since I1 < I2 and VQ1 + R1 * I1 > VQ2, there is an equilibrium point where V1 = V2, and at this time V1 - V2 = 0, and the loop stops balancing.

[0169] For Examples 1 to 5, the above formula contains the terms ΔT3*ΔT4 and ΔT4. Because the actual measurement revealed a quadratic relationship between wind speed and the temperature difference ΔT at points equidistant from both ends of the sensor's heating wire, the wind speed and the sensor's output voltage exhibit a maximum fourth-order relationship. In the design, the first PNP-type BJT transistor combination 1031 and the second PNP-type BJT bipolar transistor combination 1032 on the MEMS chip side are placed in the substrate and are farther from the central heating wire 101 than the first temperature-sensitive resistor sensor 1021 and the second temperature-sensitive resistor sensor 1022. Here, the curvature of the temperature difference ΔT4 curve is low and the peak value is close to 0. Therefore, the curve of the output voltage V within the tested wind speed range of 0~1m / s can be considered a cubic function. Therefore, this system containing both a MEMS chip and an ASIC compensation chip can achieve the compensation principle described in the invention.

Claims

1. A MEMS chip for sensing thermal gas flow rate, comprising: The substrate, wherein the substrate is a single-crystal silicon crystal orientation (100) wafer, is characterized in that it further comprises: a central heating wire (101), a first temperature-sensitive resistive sensor (1021), a second temperature-sensitive resistive sensor (1022), a first BJT bipolar transistor assembly, a second BJT bipolar transistor assembly, and a thermal bridge (106); the central heating wire (101) is located at the central axis of symmetry on the thermal bridge (106); a thermal insulation cavity (105) is provided at the bottom of the thermal bridge (106), the thermal insulation cavity (105) being heated along the center... The two ends of the heating filament (101) perpendicular to the arrangement direction are connected to the thermal bridge (106); the outside of the insulation cavity (105) is a substrate; the first temperature-sensitive resistor sensor and the second temperature-sensitive resistor sensor are connected in series to form a half-arm Wheatstone bridge and are located at equidistant positions at both ends of the central heating filament (101) and on the thermal bridge; the first BJT bipolar transistor combination and the second BJT bipolar transistor combination are located on the substrates on both sides of the insulation cavity (105) along the arrangement direction of the central heating filament (101); the first BJT bipolar transistor... The transistor assembly and the second BJT bipolar transistor assembly are equidistant from the heating wire. The first BJT bipolar transistor assembly includes a first BJT transistor and a second BJT transistor, wherein the collectors and bases of the N basic BJT transistor units of the first BJT transistor are short-circuited and connected in parallel, and the collectors and bases of the M basic BJT transistor units of the second BJT transistor are short-circuited and connected in parallel; the emitters of the N basic BJT transistor units of the first BJT transistor are connected in parallel, and the emitters of the M basic BJT transistor units of the second BJT transistor are connected in parallel. The emitters are connected in parallel; the second BJT bipolar transistor combination includes a third BJT transistor and a fourth BJT transistor, wherein the collectors and bases of the N basic BJT transistor units of the third BJT transistor are short-circuited and connected in parallel, and the collectors and bases of the M basic BJT transistor units of the fourth BJT transistor are short-circuited and connected in parallel; the emitters of the N basic BJT transistor units of the third BJT transistor are connected in parallel, and the emitters of the M basic BJT transistor units of the fourth BJT transistor are connected in parallel; N is greater than or equal to 2, and M is greater than or equal to 1.

2. The MEMS chip terminal for the thermally sensing gas flow sensor according to claim 1, characterized in that: The first BJT bipolar transistor combination is a first PNP type BJT transistor combination (1031); the second BJT bipolar transistor combination is a second PNP type BJT bipolar transistor combination (1032); the first PNP type BJT transistor combination (1031) and the second PNP type BJT bipolar transistor combination (1032) have the same structure.

3. The MEMS chip terminal for the thermally sensing gas flow sensor according to claim 2, characterized in that: The insulation cavity of the insulation cavity (105) is in the shape of an inverted frustum.

4. The MEMS chip terminal for the thermal gas flow sensor according to claim 3, characterized in that: It also includes an ambient temperature sensor (104) and a heating wire constant temperature difference control module. The ambient temperature sensor (104) is used to connect to the heating wire constant temperature difference control module. The center heating wire (101), the first temperature-sensitive resistor sensor (1021) and the second temperature-sensitive resistor sensor (1022) are made of platinum metal, and the thermal bridge (106) is made of silicon dioxide or silicon nitride.

5. A linear compensation system for a thermally sensing gas flow sensor, characterized in that: The MEMS chip for a thermally sensing gas flow sensor, as described in any one of claims 1 to 4, further includes: a first loop, a first shunt circuit, a second loop, and a second shunt circuit; the first output terminal of the first loop is connected to the input terminal of a first BJT transistor, and the second output terminal of the first loop is connected to the input terminal of a second BJT transistor; the shunt terminal of the first loop is connected to the input terminal of the first shunt circuit, and the output terminal of the first shunt circuit is connected to the input terminal of a first temperature-sensitive resistive sensor (1021); the first output terminal of the second loop is connected to the input terminal of a third BJT transistor, and the second output terminal of the second loop is connected to the input terminal of a fourth BJT transistor; the shunt terminal of the second loop is connected to the input terminal of the second shunt circuit, and the output terminal of the second shunt circuit is connected to the input terminal of a second temperature-sensitive resistive sensor (1022).

6. The linear compensation system for a thermally sensing gas flow sensor according to claim 5, characterized in that: It also includes a loop starter; the loop starter drives the first loop and the second loop to operate respectively; the first loop includes a first voltage-controlled current generator, a first voltage differencer and a first load impedance, the first current output terminal of the first voltage-controlled current generator flows through the first load impedance and the first BJT transistor, and the second current output terminal of the first voltage-controlled current generator flows through the second BJT transistor. The sum of the voltage of the first load impedance and the voltage of the first BJT transistor is connected to the first input terminal of the first voltage differencer. The voltage output terminal of the second BJT transistor is connected to the second input terminal of the first voltage differencer. The output terminal of the first voltage differencer is connected to the control terminal of the first voltage-controlled current generator. The second loop includes the second voltage-controlled current generator, the second voltage differencer, and the second load impedance. The first current output terminal of the second voltage-controlled current generator flows through the third BJT transistor. The second current output terminal of the second voltage-controlled current generator flows through the second load impedance and the fourth BJT transistor. The voltage output terminal of the third BJT transistor is connected to the first input terminal of the second voltage differencer. The sum of the second load impedance and the voltage of the fourth BJT transistor is connected to the second input terminal of the second voltage differencer. The output terminal of the second voltage differencer is connected to the control terminal of the second voltage control current generator. The first shunt circuit is a first current amplifier, and the second shunt circuit is a second current amplifier; the output terminal of the first voltage differencer is connected to the input terminal of the first current amplifier, the output terminal of the first current amplifier is connected to the non-series terminal of the first temperature-sensitive resistor sensor (1021), the output terminal of the second voltage differencer is connected to the input terminal of the second current amplifier, and the output terminal of the second current amplifier is connected to the non-series terminal of the second temperature-sensitive resistor sensor (1022).

7. A linear compensation system for a thermally sensing gas flow sensor, characterized in that: The MEMS chip for a thermally sensing gas flow sensor, as described in any one of claims 1 to 4, further includes: a first loop, a first replication circuit, a second loop, and a second replication circuit; the first output terminal of the first loop is connected to the input terminal of a first BJT transistor, and the second output terminal of the first loop is connected to the input terminal of a second BJT transistor; the first replication circuit replicates the current of either the first or second BJT transistor; the output terminal of the first replication circuit is connected to the input terminal of a first temperature-sensitive resistive sensor (1021); the first output terminal of the second loop is connected to the input terminal of a third BJT transistor, and the second output terminal of the second loop is connected to the input terminal of a fourth BJT transistor; the second replication circuit replicates either the third or fourth BJT transistor. The current; the output of the second replication circuit is connected to the input of the second temperature-sensitive resistive sensor (1022).

8. The linear compensation system for a thermally sensing gas flow sensor according to claim 7, characterized in that: It also includes a first loop, a second loop, and a loop starter; the loop starter drives the first loop and the second loop to operate respectively; the first loop includes a first voltage-controlled current generator, a first voltage differencer, and a first load impedance; the first current output terminal of the first voltage-controlled current generator flows through the first load impedance and the first BJT transistor, and the second current output terminal of the first voltage-controlled current generator flows through the second BJT transistor. The sum of the voltage of the first load impedance and the voltage of the first BJT transistor is connected to the first input terminal of the first voltage differencer. The voltage output terminal of the second BJT transistor is connected to the second input terminal of the first voltage differencer. The output terminal of the first voltage differencer is connected to the control terminal of the first voltage-controlled current generator. The second loop includes the second voltage-controlled current generator, the second voltage differencer, and the second load impedance. The first current output terminal of the second voltage-controlled current generator flows through the third BJT transistor. The second current output terminal of the second voltage-controlled current generator flows through the second load impedance and the fourth BJT transistor. The voltage output terminal of the third BJT transistor is connected to the first input terminal of the second voltage differencer; the sum of the voltage of the second load impedance and the voltage of the fourth BJT transistor is connected to the second input terminal of the second voltage differencer; the output terminal of the second voltage differencer is connected to the control terminal of the second voltage-controlled current generator; the first replication circuit is a first current replication circuit, and the second replication circuit is a second current replication circuit. The first current replication circuit replicates the emitter current of the first BJT transistor, and the second current replication circuit replicates the emitter current of the fourth BJT transistor; the output terminals of the first current replication circuit and the second current replication circuit are respectively connected to the non-series terminals of the first temperature-sensitive resistive sensor (1021) and the second temperature-sensitive resistive sensor (1022).

9. The linear compensation system for a thermally sensing gas flow sensor according to claim 7 or 8, characterized in that: It also includes a current reference source, which is used to drive a first voltage differencer and a second voltage differencer.

10. A linear compensation system for a thermally sensing gas flow sensor, characterized in that: The MEMS chip terminal for the thermally sensing gas flow sensor as described in claim 4 includes a heating wire constant temperature difference control module comprising: a first voltage divider, a second voltage divider, and a third voltage differencer; the first voltage divider includes a first external resistor (Ra), one end of which is connected in series with an ambient temperature sensor (104); the second voltage divider includes a second external resistor (Rb), one end of which is connected in series with a central heating wire (101); the other ends of the first external resistor (Ra) and the second external resistor (Rb) are connected; the other ends of the ambient temperature sensor (104) and the central heating wire (101) are grounded; the connection between the first external resistor (Ra) and the ambient temperature sensor (104) is connected to the first input terminal of the third voltage differencer; the connection between the second external resistor (Rb) and the central heating wire (101) is connected to the second input terminal of the third voltage differencer; and the output terminal of the third voltage differencer is connected to the connection between the first external resistor (Ra) and the second external resistor (Rb).

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