阅读说明：本技术 基于mems气体传感器阵列的气体检测系统 (Gas detection system based on MEMS gas sensor array ) 是由 许磊 谷文先 祁伟杰 王晶 于 2020-12-18 设计创作，主要内容包括：本发明公开了一种基于MEMS气体传感器阵列的气体检测系统,包括：MEMS气体传感器阵列、分时复用的多通道电阻频率转换电路、可编程的加热器电路、EEPROM、可修调的片内振荡器、上电自复位电路以及数字控制电路；所述MEMS气体传感器阵列包括多个气体传感器；所述气体传感器包括加热器电阻和气敏材料电阻；其中,所述MEMS气体传感器阵列用于将环境中的气体信息转换为所述气敏材料电阻的变化；所述多通道电阻频率转换电路用于将选中通道的气敏材料的电阻值转化为相应频率的方波信号；所述片内振荡器用于产生稳定的系统所需时钟信号。应用本发明提供的技术方案,可以降低工作电压和电路功耗,并提高气体传感器中气敏材料电阻的检测范围与检测精度。(The invention discloses a gas detection system based on an MEMS gas sensor array, which comprises: the system comprises an MEMS gas sensor array, a time-sharing multiplexing multi-channel resistance frequency conversion circuit, a programmable heater circuit, an EEPROM, a trimmable on-chip oscillator, an electrifying self-resetting circuit and a digital control circuit; the MEMS gas sensor array comprises a plurality of gas sensors; the gas sensor comprises a heater resistor and a gas-sensitive material resistor; wherein the MEMS gas sensor array is used for converting gas information in the environment into the change of the resistance of the gas-sensitive material; the multi-channel resistance frequency conversion circuit is used for converting the resistance value of the gas sensitive material of the selected channel into a square wave signal with corresponding frequency; the on-chip oscillator is used for generating a stable system required clock signal. By applying the technical scheme provided by the invention, the working voltage and the circuit power consumption can be reduced, and the detection range and the detection precision of the gas sensitive material resistor in the gas sensor can be improved.)

1. A gas detection system based on a MEMS gas sensor array, comprising:

the system comprises an MEMS gas sensor array, a time-sharing multiplexing multi-channel resistance frequency conversion circuit, a programmable heater circuit, an EEPROM, a trimmable on-chip oscillator, an electrifying self-resetting circuit and a digital control circuit; the MEMS gas sensor array comprises a plurality of gas sensors; the gas sensor comprises a heater resistor and a gas-sensitive material resistor;

the MEMS gas sensor array, the multi-channel resistance frequency conversion circuit, the heater circuit, the EEPROM, the on-chip oscillator and the power-on self-reset circuit are respectively connected with corresponding pins of the digital control circuit;

wherein the MEMS gas sensor array is used for converting gas information in the environment into the change of the resistance of the gas-sensitive material; the multi-channel resistance frequency conversion circuit is used for converting the resistance value of the gas sensitive material of the selected channel into a square wave signal with corresponding frequency; the heater circuit is used for configuring heating voltage of the heater resistor; the EEPROM is used for storing system configuration parameters and user data; the on-chip oscillator is used for generating a stable system required clock signal; the digital control circuit is used for completing the functions of controlling the working mode of the on-chip circuit, measuring the frequency, storing data and communicating I2C.

2. The gas detection system of claim 1, wherein the multi-channel resistive frequency conversion circuit comprises:

the resistance conversion current circuit is used for driving a reference voltage to two ends of the gas-sensitive material resistor so as to form a detection current related to the gas-sensitive material resistor;

the CMOS current mirror circuit is used for reducing the detection current to form a mirror current;

an integrating circuit for outputting a periodic triangular wave signal based on the mirror current;

and the bistable hysteresis comparator circuit is used for outputting a periodic square wave signal based on the triangular wave signal.

3. The gas detection system of claim 2, wherein the resistance-switching current circuit comprises: the positive phase input end of the first high-gain operational amplifier is used for inputting the reference voltage, the negative phase input end of the first high-gain operational amplifier is used for connecting a first node, and the output end of the first high-gain operational amplifier is connected with the grid electrode of the driving transistor; the drain electrode of the driving transistor is connected with a second node, and the source electrode of the driving transistor is connected with the first node; the second node is connected with the CMOS current mirror circuit;

one end of each gas-sensitive material resistor is grounded, and the other end of each gas-sensitive material resistor is connected with the first node through an independent numerical control switch; the digital control circuit provides a switch control signal for the numerical control switch.

4. The gas detection system of claim 2, wherein the CMOS current mirror circuit comprises: a PMOS current mirror and an NMOS current mirror;

the PMOS current mirror includes: first to sixth transistors; the grid electrodes of the first transistor, the second transistor and the fifth transistor are connected, the source electrodes of the first transistor, the second transistor and the fifth transistor are respectively connected with a power supply end through independent numerical control switches, the drain electrode of the first transistor is connected with the grid electrode of the first transistor and the source electrode of the third transistor, the drain electrode of the second transistor is connected with the source electrode of the fourth transistor, and the drain electrode of the fifth transistor is connected with the source electrode of the sixth transistor; the grid electrodes of the third transistor, the fourth transistor and the sixth transistor are connected, the drain electrode of the third transistor is connected with a second node, the second node is connected with the resistance conversion current circuit, the drain electrode of the fourth transistor is connected with a third node, and the drain electrode of the sixth transistor is connected with a fourth node;

the NMOS current mirror includes: seventh to tenth transistors; the grid electrodes of the seventh transistor and the eighth transistor are connected, the drain electrode of the seventh transistor is connected with the third node, the drain electrode of the eighth transistor is connected with the fourth node, the source electrode of the seventh transistor is connected with the grid electrode and the drain electrode of the ninth transistor, and the source electrode of the eighth transistor is connected with the drain electrode of the tenth transistor; the sources of the ninth transistor and the tenth transistor are respectively grounded through a single numerical control switch.

5. The gas detection system of claim 4, wherein the integration circuit comprises:

the source electrode of the fifth transistor is connected with the numerical control switch;

the source electrode of the tenth transistor is connected with the numerical control switch;

and one polar plate of the storage capacitor is grounded, and the other polar plate of the storage capacitor is connected with the fourth node.

6. The gas detection system of claim 2, wherein the bistable hysteresis comparator circuit comprises: the second high-gain operational amplifier, the third high-gain operational amplifier, the first resistor and the second resistor;

the positive phase input end of the second high-gain operational amplifier is connected with the reference voltage, and the negative phase input end of the second high-gain operational amplifier is connected with the output end of the second high-gain operational amplifier;

the negative phase input end of the third high-gain operational amplifier is connected with a fourth node, and the positive phase input end of the third high-gain operational amplifier is connected with the output end of the third high-gain operational amplifier through the first resistor and is connected with the output end of the second high-gain operational amplifier through the second resistor;

wherein the fourth node is connected with the CMOS current mirror circuit; and the output end of the third high-gain operational amplifier is connected with a plurality of inverters which are connected in series.

7. The gas detection system of claim 1, wherein the digital control circuit has an EEPROM control module connected to the EEPROM by a low dropout linear regulator.

8. The gas detection system of claim 1, wherein the digital control circuit has a trimming circuit control module that drives the on-chip oscillator through a trimming circuit, the on-chip oscillator providing a clock signal to the digital control circuit.

9. The gas detection system of claim 1, wherein the digital control circuit has an RTF measurement circuit connected to the multi-channel resistance frequency conversion circuit, the RTF measurement circuit being configured to provide a switching control signal to the multi-channel resistance frequency conversion circuit and to measure the frequency of the square wave signal via the digital circuit.

10. The gas detection system of claim 1, wherein the digital control circuit has a heater control module coupled to the heater circuit, the heater control module configured to configure a value received from an external controller to an input of the heater circuit.

Technical Field

The invention relates to the field of semiconductor integrated circuits, in particular to a gas detection system based on an MEMS gas sensor array.

Background

The odor identification technology has very wide application requirements in the fields of intelligent terminals, environment monitoring and the like. Currently, mass spectrometers, gas chromatographs and fourier transform infrared spectrometers are used for gas detection, but these systems are bulky, expensive and complex. In recent years, there has been a growing concern about environmental quality and safety, and the demand for portable, low-cost, and low-power consumption gas sensing systems has increased year by year.

The gas detection system consists of a gas sensor or a gas sensor array and an interface circuit. Currently, a readout circuit based on a resistance frequency conversion (RTF) circuit is widely used because of its simple design, high dynamic range and good linearity compared to an ADC. But many studies are focused on achieving high dynamic range and linearity, rather than designing the circuit from a system perspective. These resistive frequency translation circuits ignore the digital translation of the frequency. Therefore, these circuits can be used in a resistance frequency conversion laboratory instrument or a gas detection system, but there is no gas detection system for such an integrated digital output MEMS gas sensor array.

Disclosure of Invention

In view of this, the invention provides a gas detection system based on an MEMS gas sensor array, which can reduce working voltage and circuit power consumption, improve sensor selectivity, reduce sensor cross sensitivity, and improve detection range and detection accuracy of gas sensitive material resistance in a gas sensor, thereby facilitating sensor data acquisition and processing.

In order to achieve the above purpose, the invention provides the following technical scheme:

a gas detection system, comprising:

the system comprises an MEMS gas sensor array, a time-sharing multiplexing multi-channel resistance frequency conversion circuit, a programmable heater circuit, an EEPROM, a trimmable on-chip oscillator, an electrifying self-resetting circuit and a digital control circuit; the MEMS gas sensor array comprises a plurality of gas sensors, wherein each gas sensor comprises a heater resistor and a gas sensitive material resistor;

the MEMS gas sensor array, the multi-channel resistance frequency conversion circuit, the heater circuit, the EEPROM, the on-chip oscillator and the power-on self-reset circuit are respectively connected with corresponding pins of the digital control circuit;

wherein the MEMS gas sensor array is used for converting gas information in the environment into the change of the resistance of the gas-sensitive material; the multi-channel resistance frequency conversion circuit is used for converting the resistance value of the gas sensitive material of the selected channel into a square wave signal with corresponding frequency; the heater circuit is used for configuring heating voltage of the heater resistor; the EEPROM is used for storing system configuration parameters and user data; the on-chip oscillator is used for generating a stable system required clock signal; the digital control circuit is used for completing the functions of controlling the working mode of the on-chip circuit, measuring the frequency, storing data and communicating I2C.

Preferably, in the gas detection system described above, the multichannel resistance frequency conversion circuit includes:

the resistance conversion current circuit is used for driving a reference voltage to two ends of the gas-sensitive material resistor so as to form a detection current related to the gas-sensitive material resistor;

the CMOS current mirror circuit is used for reducing the detection current to form a mirror current;

an integrating circuit for outputting a periodic triangular wave signal based on the mirror current;

and the bistable hysteresis comparator circuit is used for outputting a periodic square wave signal based on the triangular wave signal.

Preferably, in the gas detection system described above, the resistance-switching current circuit includes: the positive phase input end of the first high-gain operational amplifier is used for inputting the reference voltage, the negative phase input end of the first high-gain operational amplifier is used for connecting a first node, and the output end of the first high-gain operational amplifier is connected with the grid electrode of the driving transistor; the drain electrode of the driving transistor is connected with a second node, and the source electrode of the driving transistor is connected with the first node; the second node is connected with the CMOS current mirror circuit;

one end of each gas-sensitive material resistor is grounded, and the other end of each gas-sensitive material resistor is connected with the first node through an independent numerical control switch; the digital control circuit provides a switch control signal for the numerical control switch.

Preferably, in the gas detection system described above, the CMOS current mirror circuit includes: a PMOS current mirror and an NMOS current mirror;

the PMOS current mirror includes: first to sixth transistors; the grid electrodes of the first transistor, the second transistor and the fifth transistor are connected, the source electrodes of the first transistor, the second transistor and the fifth transistor are respectively connected with a power supply end through independent numerical control switches, the drain electrode of the first transistor is connected with the grid electrode of the first transistor and the source electrode of the third transistor, the drain electrode of the second transistor is connected with the source electrode of the fourth transistor, and the drain electrode of the fifth transistor is connected with the source electrode of the sixth transistor; the grid electrodes of the third transistor, the fourth transistor and the sixth transistor are connected, the drain electrode of the third transistor is connected with a second node, the second node is connected with the resistance conversion current circuit, the drain electrode of the fourth transistor is connected with a third node, and the drain electrode of the sixth transistor is connected with a fourth node;

the NMOS current mirror includes: seventh to tenth transistors; the grid electrodes of the seventh transistor and the eighth transistor are connected, the drain electrode of the seventh transistor is connected with the third node, the drain electrode of the eighth transistor is connected with the fourth node, the source electrode of the seventh transistor is connected with the grid electrode and the drain electrode of the ninth transistor, and the source electrode of the eighth transistor is connected with the drain electrode of the tenth transistor; the sources of the ninth transistor and the tenth transistor are respectively grounded through a single numerical control switch.

Preferably, in the above gas detection system, the integration circuit includes:

the source electrode of the fifth transistor is connected with the numerical control switch;

the source electrode of the tenth transistor is connected with the numerical control switch;

and one polar plate of the storage capacitor is grounded, and the other polar plate of the storage capacitor is connected with the fourth node.

Preferably, in the gas detection system, the bistable hysteresis comparator circuit includes: the second high-gain operational amplifier, the third high-gain operational amplifier, the first resistor and the second resistor;

the positive phase input end of the second high-gain operational amplifier is connected with the reference voltage, and the negative phase input end of the second high-gain operational amplifier is connected with the output end of the second high-gain operational amplifier;

the negative phase input end of the third high-gain operational amplifier is connected with a fourth node, and the positive phase input end of the third high-gain operational amplifier is connected with the output end of the third high-gain operational amplifier through the first resistor and is connected with the output end of the second high-gain operational amplifier through the second resistor;

wherein the fourth node is connected with the CMOS current mirror circuit; and the output end of the third high-gain operational amplifier is connected with a plurality of inverters which are connected in series.

Preferably, in the above gas detection system, the digital control circuit has an EEPROM control module, and the EEPROM control module is connected to the EEPROM through a low dropout linear regulator.

Preferably, in the above gas detection system, the digital control circuit has a trimming circuit control module, the trimming circuit control module drives the on-chip oscillator through the trimming circuit, and the on-chip oscillator provides a clock signal for the digital control circuit.

Preferably, in the above gas detection system, the digital control circuit has an RTF measurement circuit connected to the multi-channel resistance frequency conversion circuit, and the RTF measurement circuit is configured to provide a switch control signal to the multi-channel resistance frequency conversion circuit and measure the frequency of the square wave signal through the digital circuit.

Preferably, in the above gas detection system, the digital control circuit has a heater control module, the heater control module is connected to the heater circuit, and the heater control module is configured to configure a value received from an external controller to an input terminal of the heater circuit.

It can be known from the above description that in the gas detection system based on the MEMS gas sensor array provided in the technical solution of the present invention, the time-division multiplexing multi-channel resistance frequency conversion circuit is used to replace the conventional analog-to-digital converter detection circuit, so that the influence of the voltage variation at both ends of the gas sensitive material resistance on the sensor accuracy is eliminated, the design of the analog-to-digital conversion circuit is simplified, the tunable on-chip oscillator is used to generate a stable system clock signal, the dependence on the external clock is avoided, and the I2C interface is used to communicate with a computer or other micro control devices, thereby facilitating the acquisition, processing and use of data. On the whole, working voltage and circuit power consumption are reduced, selectivity of the sensor is improved, cross sensitivity of the sensor is reduced, detection range and detection precision of gas sensitive material resistance in the gas sensor are improved, and data acquisition and processing of the sensor are facilitated.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced below, it is obvious that the drawings in the following description are only embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

The structure, proportion, size and the like shown in the drawings are only used for matching with the content disclosed in the specification, so that the person skilled in the art can understand and read the description, and the description is not used for limiting the limit condition of the implementation of the invention, so the method has no technical essence, and any structural modification, proportion relation change or size adjustment still falls within the scope of the technical content disclosed by the invention without affecting the effect and the achievable purpose of the invention.

Fig. 1 is a schematic structural diagram of a gas detection system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a multi-channel resistance frequency conversion circuit according to an embodiment of the present invention;

fig. 3 is a schematic diagram of a CMOS current mirror circuit according to an embodiment of the present invention;

fig. 4 is a schematic diagram of a circuit of an on-chip oscillator capable of trimming according to an embodiment of the present invention.

Detailed Description

Embodiments of the present application will now be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the application are shown, and in which it is to be understood that the embodiments described are merely illustrative of some, but not all, of the embodiments of the application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

In order to make the aforementioned objects, features and advantages of the present application more comprehensible, the present application is described in further detail with reference to the accompanying drawings and the detailed description.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a gas detection system based on a MEMS gas sensor array according to an embodiment of the present invention. As shown in fig. 1, the gas detection system includes:

a MEMS gas sensor array 11, a time-division multiplexing multi-channel resistance frequency conversion circuit 12, a programmable heater circuit 14, an EEPROM15, a trimmable on-chip oscillator 18, a power-on self-reset circuit 19 and a digital control circuit 13; the MEMS gas sensor array 11 comprises a plurality of gas sensors; the gas sensor comprises a heater resistor and a gas-sensitive material resistor;

the MEMS gas sensor array 11, the multi-channel resistance frequency conversion circuit 12, the heater circuit 14, the EEPROM15, the on-chip oscillator 18 and the power-on self-reset circuit 19 are respectively connected with corresponding pins of the digital control circuit 13;

the MEMS gas sensor array 11 is used for converting gas information in the environment into the change of the resistance of the gas-sensitive material; the multi-channel resistance frequency conversion circuit 12 is configured to convert the resistance value of the gas sensitive material of the selected channel into a square wave signal with a corresponding frequency, for example, the digital control circuit 13 may control the channel for switching the sampling, and convert the resistance value of the gas sensitive material into a square wave signal with a corresponding frequency; the heater circuit 14 is configured to configure a heating voltage of the heater resistor, wherein the heater resistor is used to heat the gas sensitive material resistor to provide a suitable working temperature for the gas sensitive material resistor; the EEPROM15 is used for saving system configuration parameters and user data; the on-chip oscillator 18 is used for generating a clock signal Clk1 required for stabilizing the system; the digital control circuit 13 is used for performing the functions of controlling the working mode of the on-chip circuit, measuring the frequency, storing data and communicating I2C. I2C is used to communicate directly with the microcontroller or indirectly with the computer from the slave interface module 34.

The programmable heater circuit 14 is composed of a plurality of adjustable linear voltage regulators, and can be controlled by the digital control circuit 13 to realize switching and switching of suitable working voltages of a plurality of preset sensors as required, the stepping precision reaches 0.1V, and different working voltages are used for driving the MEMS gas sensor array 11, thereby being beneficial to improving the selectivity of the gas sensor. The EEPROM15 is a memory for storing the configuration of the gas detection system and user data, so that power failure data is not lost, and the detection system can be conveniently restored to a working state before power failure. The power-on self-reset circuit 19 automatically generates a reset signal after the gas detection system is powered on, and the reset signal is used for the global reset of the digital control circuit 13 so as to ensure that the digital control circuit 13 is in a determined working state after being powered on.

In the embodiment of the present invention, the MEMS gas sensor array 11 may load the same or different gas-sensitive materials on the array by using an MEMS process, convert information of different gases or gases with different concentrations into an electrical signal according to an oxidation-reduction principle, configure a plurality of gas-sensitive material resistors in the MEMS gas sensor array 11 into different operating modes, and process response signals thereof, which may reduce cross sensitivity of the sensors.

Referring to fig. 2, fig. 2 is a schematic diagram of a multi-channel resistance frequency conversion circuit according to an embodiment of the present invention. As shown in fig. 2, the multi-channel resistance frequency conversion circuit 12 includes: a resistance-switching current circuit 21 for converting the reference voltage V_RSENDriven to the gas sensitive material resistance R_sensorSo as to form a resistance R with said gas sensitive material_sensorAssociated detection current, i.e. gas-sensitive material resistance R_sensorIs biased at the gas sensitive material resistor R_sensorThe voltage at the two ends is kept constant, so that the influence of the change of the driving voltage on the accuracy of the sensor is reduced; a CMOS current mirror circuit 22 for reducing the detection current to form a mirror current; an integration circuit 23 for outputting a current based on the mirror currentPeriodic triangular wave signals; and the bistable hysteresis comparator circuit 24 is used for outputting a periodic square wave signal based on the triangular wave signal.

The resistance conversion current circuit 21, the CMOS current mirror circuit 22, the integrating circuit 23, and the bistable hysteresis comparator circuit 24 are connected in sequence. The resistance-switching current circuit 21 uses the first high-gain OPA1 to couple the reference voltage V_RSENDriven to gas sensitive material resistance R_sensorThe digital control circuit 13 is used for controlling the on-off of the switches S1-S4, only one corresponding switch is turned on after decoding each time, the other switches are turned off, and the gas sensitive material resistor R is connected with the gas sensitive material resistor R_sensorThe voltage at two ends is the driving voltage set by the multi-channel heater circuit, the voltage is kept constant, and the generated current and the gas sensitive material resistance R are in accordance with ohm's law_sensorIn an inversely proportional relationship, the current flows to the CMOS current mirror circuit 22, forming a mirror current, which is mirrored to the oscillation circuit.

It should be noted that, in fig. 2, the control switches S1-S4 are controlled by the Channel _ sel signal output by the digital control circuit 13 in fig. 1, only one switch is closed each time, the sensors in the MEMS gas sensor array 11 are connected into the circuit after the switches are closed, and each sensor in the MEMS gas sensor array 11 is equivalent to a resistor, such as the gas sensitive material resistor R in fig. 2_sensorAs shown.

As shown in fig. 2, the resistance-switching current circuit 21 includes: a first high-gain operational amplifier OPA1 with high gain when the gain is greater than 60db, and a non-inverting input terminal thereof for inputting the reference voltage V_RSENA negative phase input end of the driving transistor M0 is connected with the first node 01, and an output end of the driving transistor M0 is connected with the grid electrode of the driving transistor M0; the drain electrode of the driving transistor M0 is connected with a second node 02, and the source electrode is connected with the first node 01; the second node 02 is connected with the CMOS current mirror circuit 22; wherein all of the gas sensitive material resistances R_sensorOne end of each of the first node 01 and the second node is grounded, and the other end of each of the first node 01 and the second node is connected with the first node through a single numerical control switch; the digital control circuit 13 provides a switch control signal for the numerical control switch, and the digital control circuit 13 can control a channel for switching sampling so as to make the gas sensitive materialMaterial resistance R_sensorThe resistance value of (a) is converted into a square wave signal of the corresponding frequency.

It should be noted that, only four resistors are shown in the figure and connected to one digitally controlled switch, and the number of resistors and the number of corresponding digitally controlled switches are set based on requirements and are not limited to 4.

In an embodiment of the present invention, the CMOS current mirror circuit includes: PMOS current mirrors and NMOS current mirrors. As shown in fig. 3, fig. 3 is a schematic diagram of a CMOS current mirror circuit according to an embodiment of the present invention.

Wherein the PMOS current mirror comprises: first to sixth transistors M1 to M6, the first to sixth transistors M1 to M6 being all PMOS; the gates of the first transistor M1, the second transistor M2 and the fifth transistor M5 are connected, the sources of the three are respectively connected to a power supply terminal through a separate numerical control switch, for example, the source of the first transistor M1 is connected to the power supply terminal through a numerical control switch S5, the source of the second transistor M2 is connected to the power supply terminal through a numerical control switch S6, the source of the fifth transistor M5 is connected to the power supply terminal through a numerical control switch S7, the drain of the first transistor M1 is connected to the gate thereof and the source of the third transistor M3, the drain of the second transistor M2 is connected to the source of the fourth transistor M4, and the drain of the fifth transistor M5 is connected to the source of the sixth transistor M6; the gates of the third transistor M3, the fourth transistor M4 and the sixth transistor M6 are connected, the drain of the third transistor M3 is connected to the second node 02, the second node 02 is connected to the resistance-switching current circuit, the drain of the fourth transistor M4 is connected to the third node 03, and the drain of the sixth transistor M6 is connected to the fourth node 04;

wherein the NMOS current mirror comprises: seventh to tenth transistors M7 to M10, the seventh to tenth transistors M7 to M10 being all NMOS; the gates of the seventh transistor M7 and the eighth transistor M8 are connected, the drain of the seventh transistor M7 is connected to the third node 03, the drain of the eighth transistor M8 is connected to the fourth node 04, the source of the seventh transistor M7 is connected to the gate and the drain of the ninth transistor M9, and the source of the eighth transistor M8 is connected to the drain of the tenth transistor M10; the sources of the ninth transistor M9 and the tenth transistor M10 are grounded through separate digitally controlled switches, for example, the source of the ninth transistor M9 is grounded through the digitally controlled switch S8, and the source of the tenth transistor M10 is grounded through the digitally controlled switch S9.

In fig. 3, n: 1 represents the ratio of I1 to I2, and 1:1 represents the ratio of I2 to I3.

In the embodiment of the present invention, the CMOS current mirror circuit 22 is a cascode current mirror, the first transistor M1 and the second transistor M2 form a current mirror, so that the drain voltage of the transistor M1 is the same as the drain voltage of the transistor M2, and the current mirror structure formed by the transistors M3 and M4 precisely replicates current, so that the CMOS current mirror circuit suppresses the channel length modulation effect by using the cascode structure, which is beneficial to reducing mismatch when replicating a current source, and the gas sensitive material resistor R is adjusted by adjusting the ratio of the first transistor M1, the second transistor M2, the third transistor M3 and the fourth transistor M4 in the PMOS current mirror_sensorThe generated current is reduced by n times, and the reduced current is provided for a charging path of a rear-stage integrating circuit through a fifth transistor M5 and a sixth transistor M6, so that the power consumption of the circuit is reduced. The seventh transistor M7, the eighth transistor M8, the ninth transistor M9 and the tenth transistor M10 in the NMOS current mirror form a cascode current mirror in the same form, receive the current output by the fourth transistor M4, and provide a discharge path of the same current for the integrating circuit.

The CMOS current mirror circuit 22 scales down the current generated by the pre-stage resistance conversion current circuit 21 to realize lower power consumption, and the CMOS current mirror circuit 22 makes the gas sensitive material resistance R_sensorThe converted current is mirrored to a later stage circuit for charging the integrating circuit 23.

In an embodiment of the present invention, the integrating circuit 23 includes: a numerical control switch S7 is connected with the source electrode of the fifth transistor M5; a digitally controlled switch S9 connected to the source of the tenth transistor M10; and one polar plate of the storage capacitor C is grounded, and the other polar plate is connected with the fourth node 04.

Wherein the integrating circuit 23 comprises two operating states: first, the CMOS current mirror circuit 22 charges the integrating circuit 23 to generate a rising linear ramp signal; second, qiResistance R of sensitive material_sensorThe converted current discharges the integrating circuit 23, generating a falling linear ramp signal, and finally generating a periodic triangular wave signal.

In the embodiment of the present invention, a transmission gate is used as a control switch of the integrating circuit 23 to reduce the on-resistance and enhance the linearity of the circuit. The control signal of the switch is generated by an inverter group in the bistable hysteresis comparator circuit 24, a numerical control switch S7 is placed in a charging circuit, when a numerical control switch S7 is closed, the numerical control switch S9 is switched off, the current generated by a preceding stage current mirror is copied one by one, the copied current is used for charging a storage capacitor C, the voltage on the storage capacitor C is the initial voltage plus the integral of the current intensity to the time, and therefore a slope signal which rises linearly is generated; when the numerical control switch S9 is closed and the numerical control switch S7 is opened, the storage capacitor C is discharged through the charge pump circuit, the voltage on the storage capacitor C is the initial voltage minus the integral of the current intensity over time, and the voltage on the storage capacitor C is a ramp signal that linearly decreases. The rising ramp signal and the falling ramp signal form a periodic triangular wave signal. The periodic triangular wave voltage signal is transmitted to the post-stage bistable hysteresis comparator circuit 24.

In the embodiment of the present invention, the bistable hysteresis comparator circuit 24 includes: the second high-gain operational amplifier OPA2, the third high-gain operational amplifier OPA3, the first resistor R1 and the second resistor R2; the non-inverting input terminal of the second high-gain operational amplifier OPA2 is connected to the reference voltage V_REFThe negative phase input end of the power supply is connected with the output end of the power supply; the negative phase input end of the third high-gain operational amplifier OPA3 is connected with the fourth node 04, the positive phase input end thereof is connected with the output end thereof through the first resistor R1, and the output end of the second high-gain operational amplifier OPA2 is connected through the second resistor R2; wherein the fourth node 04 is connected to the CMOS current mirror circuit 22; the output end of the third high-gain OPA3 is connected with a plurality of inverters connected in series.

Wherein the bistable hysteresis comparator circuit 24 comprises two threshold voltages V_T+、V_T-As shown in the formula (1) (2):

vc is a triangular wave signal, V, generated by the integrating circuit 23_OH、V_OLThe maximum output voltage and the minimum output voltage of the third high-gain OPA3, respectively, ultimately produce an output square wave with a duty cycle of 50%,to output the inverse of a square wave.

In the embodiment of the invention, two threshold voltages V can be adjusted_T+And V_T-Comparing with the triangular wave signal generated by the integrating circuit 23, outputting a square wave signal with corresponding frequency, and using the square wave signal as a control signal of the circuit, wherein the duty ratio of the square wave signal is 50% and remains unchanged, and finally realizing the resistance R of the gas sensitive material_sensorTo increase the stability of the bistable hysteretic comparator circuit 24, the reference voltage of the comparator is input by a voltage follower consisting of an operational amplifier.

When the voltage of the triangular wave signal Vc output by the integrating circuit 23 is greater than the positive threshold voltage V_T+When the voltage is high, the bistable hysteresis comparator circuit 24 outputs a high level; the states of the numerical control switches S7 and S9 are switched, the integrating circuit 23 starts to output a slope signal with linear descending, and when the voltage of the triangular wave signal Vc is less than the reverse threshold voltage V_T-At this time, the bistable hysteresis comparator 24 outputs a low level, and the states of the digitally controlled switches S7 and S9 are switched again. Therefore, the bistable hysteresis comparator circuit 24 converts the triangular wave signal Vc into a square wave signal with a corresponding frequency, and the corresponding frequency calculation formula is shown in formula (3):

the frequency of the square wave signal and the gas sensitive material resistance R_sensorThe resistance value of the gas sensitive material to be measured is in inverse proportion, and the resistance R of the gas sensitive material to be measured_sensorThe larger the resistance of (3), the lower the output frequency, and conversely, the higher the output frequency.

In the scheme of the invention, the gas sensitive material resistor R is used_sensorThe converted current charges and discharges the integrating circuit 23, a square wave signal with a corresponding frequency is output through the bistable comparison circuit 24, the working frequency of the square wave signal is sampled through the digital control circuit 13, and finally the square wave signal is directly communicated with the microcontroller through an I2C interface or is indirectly communicated with a computer, so that data can be conveniently acquired, processed and used.

In the embodiment of the invention, the adjustable on-chip oscillator circuit is a clock generation circuit in the chip, so that the dependence on an external clock is avoided, a stable clock signal is generated to drive the digital circuit module to work, and the application cost is reduced.

As shown in fig. 4, fig. 4 is a schematic diagram of an on-chip oscillator circuit capable of trimming according to an embodiment of the present invention, the on-chip oscillator circuit includes two identical high-speed comparators Comp1 and Comp2, two identical constant charging/discharging capacitors C1 and C2, and a combinational logic circuit, and is capable of outputting two paths of orthogonal clock signals. At the moment of power-on, Clk1 is 0, Clk2 is 1, V3 is V6 is V7 is 0, V5 is V8 is V12 is 1, when V1 is Vr, V3 is V7 is 1, V5 is 0, at this time, the signal of V8 is transmitted to V10, V12 is V8 is 0, V6 is 1, the above steps are repeated to complete the period of oscillation, the delay time of each subassembly in the circuit is ignored, and ideally, the frequency f of the generated clock is neglected_oscAs shown in equation (4):

as shown in fig. 4, the transistors M11, M14, M16, and M18 are all PMOS, and the transistors M12, M13, M15, M17, M19, and M20 are all NMOS. The sources of M11, M14, M16, M18 are all connected to the supply voltage VDD, wherein the source of M14 is connected to the source of M16 and to the supply voltage VDD via the current source Ic, the drain of M11 is connected to the drain of M12 and to the input of the second inverter 42, the gate of M11 is connected to the input of the first inverter 41 and to the output of the first and gate 45, the output of the first inverter 41 is connected to the gate of M13, the drain of M13 is connected to the gate of M12 and to the output of the high speed comparator Comp1, the source of M12 is connected to the source of M13, the drain of M14 is connected to the drain of M15 and to the non-inverting input of the high speed comparator Comp1, one plate of the capacitor C1 is connected to the source of M15 and to ground, the other plate is connected to the non-inverting input of the high speed comparator Comp1, one plate of the capacitor C2 is connected to the source of M2 and to the output of the trigger RS 3646, the drain of the M16 is connected to the drain of the M17 and the non-inverting input terminal of the high-speed comparator Comp2, the gate of the M16 is connected to the gate of the M17 and the other output terminal of the RS flip-flop 46, the source of the M15 is grounded to the source of the M17, the gate of the M18 is connected to the input terminal of the third inverter 43 and the output terminal of the second and gate 47, the drain of the M18 is connected to the input terminal of the fourth inverter 44 and the drain of the M19, the gate of the M19 is connected to the output terminal of the high-speed comparator Comp2 and the drain of the M20, the gate of the M20 is connected to the output terminal of the third inverter 43, the source of the M19 is connected to the source of the M20 and grounded, one input terminal of the RS flip-flop 46 is connected to one input terminal of the first and gate 45 and the output terminal of the fourth inverter 44, the other input terminal of the RS flip-flop 46 is connected to one input, the other input of the second and-gate 47 is connected to the output of a second buffer 49.

As shown in fig. 1, the digital control circuit 13 includes: RTF measurement circuit 31, heater control module 35, EEPROM control module 36, trimming circuit control module 37, I2C slave interface module 34, watchdog module 33, and sensor array control module 32. The digital control circuit 13 is a module that coordinates the operation of the gas detection system and communicates with an external controller.

The EEPROM control module 36 is connected with the EEPROM15 through the low dropout linear regulator 16. The EEPROM control module 36 is a module that receives a control instruction from an off-chip host to write a value in a corresponding register into the EEPROM and automatically reads all data in the EEPROM to the register in the detection chip when the power is turned on. The read-write operating voltages of the on-chip integrated EEPROMs during operation are different and have corresponding timing sequences, so the EEPROM control module 36 also needs to generate signals for switching the programming voltages, which meet the timing sequence requirements.

The trimming circuit control module 37 drives the on-chip oscillator 18 through the trimming circuit 17, and the on-chip oscillator 18 provides a clock signal Clk1 for the digital control circuit 13. The trimming circuit control module 37 may be used to adjust the frequency of the output signal of the in-oscillator 18 to output the stable clock signal Clk1 required by the system, which may reduce the effect of process corner and temperature on the system clock frequency. The trimming circuit control module 37 changes the working mode of the analog trimming circuit 17 by configuring a register in the chip, and performs the positive process corner trimming, the negative process corner trimming and the temperature trimming. The trimming circuit 17 mainly serves as a current source of the on-chip oscillator 18, and changes the output current Ic of the current source to realize the trimming of the temperature drift and the process corner.

The RTF measurement circuit 31 is connected to the multi-channel resistance frequency conversion circuit 12, and the RTF measurement circuit 31 is configured to provide a switch control signal for the multi-channel resistance frequency conversion circuit 12, and measure the frequency of the square wave signal through the digital control circuit 13. The RTF measurement circuit 31 may count and sample the square wave signals output by the time-division multiplexing multi-channel resistance frequency conversion circuit 12, the sampled channels may be switched one by using an external microcontroller or a computer to send instructions, the sampling period may also be selected by sending instructions from the external controller, the count value is stored in an internal register, and the off-chip microcontroller may output the count value after communicating with the I2C slave interface module 34.

In order to ensure the balance of the speed and the precision of measurement, the detection chip is designed with a plurality of configurable measurement times, and the measurement time is from millisecond level to second level. The frequency f of the square wave is obtained by formula conversion_cntAs shown in equation (5):

cnt in the formula (5) is the count value of the measuring module on the rising edge of the square wave signal in the measuring time, T_measureIs the measurement time for the RTF measurement circuit 31.

Wherein the heater control module 35 is connected to the heater circuit 14, and the heater control module 35 is configured to configure a value received from an external controller to an input of the heater circuit 14. Heater control module 35 may communicate with I2C slave interface module 34 via an external controller to configure the switches and output voltage values of the multiple channel linear regulators.

The I2C slave interface module 34 is a communication interface module, and can be used for communication between an off-chip controller and a gas detection system, and the I2C bus has advantages of multiple masters and the like, and is widely applied to embedded devices. In order to improve the expansibility of the detection chip, the chip adopts an I2C interface as a communication interface, an I2C slave interface module 34 mainly realizes data receiving and sending, and a host and a plurality of detection chips can be mounted on a bus, so that the host can use two IO ports, namely SCL and SDA, to complete the control and acquisition of the plurality of chips.

The watchdog module 33 completes the detection of the state of the gas detection system in a timing manner, and generates a reset signal if the gas detection system is maintained in a certain state for more than a preset time. In order to prevent the chip from entering a state where it cannot normally operate during operation, when the state machine implemented in the digital circuit remains unchanged in a certain state for a predetermined time, the watchdog module 33 generates a reset signal of the highest priority for the whole digital circuit, i.e., resets the whole digital part. After the reset signal is removed, the digital control circuit 13 will be self-started and restored to a normal working state.

Wherein the sensor array control module 32 completes scheduling between the various modules via instructions received by I2C from the slave interface module 34.

According to the scheme of the invention, the integrating circuit 23 is charged and discharged by using the current converted by the gas sensitive material resistor, the bistable comparison circuit 24 outputs a square wave signal with corresponding frequency, the digital control circuit 13 samples the working frequency of the square wave signal, and finally the working frequency is directly communicated with the microcontroller through an I2C interface or is indirectly communicated with a computer, so that the data acquisition, processing and use are facilitated.

The multichannel resistance frequency conversion circuit 12 eliminates the influence of voltage changes at two ends of the gas-sensitive material resistor on the accuracy of the sensor, reduces the current intensity in the CMOS current mirror, enlarges the detection range of the gas-sensitive material resistor, and reduces the working voltage and the circuit power consumption; the adjustable on-chip oscillator 18 in the system provides a stable and reliable clock signal Clk1 for the system, and finally the configuration of the gas detection system and the reading of the sampling value are completed through an I2C communication interface, and the sampling value is read to a microcontroller or a computer, so that the response of the MEMS gas sensor array 11 is conveniently detected, and the detection is realized by an integrated circuit process and is easy to integrate.

According to the description, the gas detection system provided by the technical scheme of the invention can measure the resistances of a plurality of gas sensors or gas sensor arrays in a time-sharing manner, keep the voltages at two ends of the gas-sensitive material resistor stable, reduce the influence of voltage change on the precision of the gas-sensitive material resistor, and improve the reproduction precision of the current mirror; the resistance value of the gas-sensitive material is converted into a frequency signal, so that the complexity of analog-to-digital conversion is reduced; the current intensity is reduced in proportion through the current mirror, low-voltage power supply can be realized, the power consumption is reduced, and the detection range and the detection precision of the gas sensitive material resistor are enlarged; the gas detection system directly outputs the converted frequency value, and can directly communicate with an external microcontroller or a computer, so that the acquisition is facilitated.

The embodiments in the present description are described in a progressive manner, or in a parallel manner, or in a combination of a progressive manner and a parallel manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments can be referred to each other.

It should be noted that in the description of the present invention, it is to be understood that the terms "upper", "lower", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only used for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. When a component is referred to as being "connected" to another component, it can be directly connected to the other component or intervening components may also be present.

It is further noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in an article or device that comprises the element.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.