CN114138034B - Programmable PWM micro-hotplate temperature control system - Google Patents
Programmable PWM micro-hotplate temperature control system Download PDFInfo
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Abstract
The invention discloses a programmable PWM micro-hotplate temperature control system, which comprises: the digital control module, and the temperature control circuit module, the reading circuit module and the IIC interface module which are connected with the digital control module. The temperature control circuit module is used for comparing the divided voltage on the heating resistor with the divided voltage on the reference resistor to determine whether to heat the heating resistor; the digital control module is mainly used for storing key information of the system and ensuring the programmability of the whole system; the reading circuit module is used for converting the selected resistance value of the temperature measuring resistor into a square wave signal with corresponding frequency and counting; the IIC interface module is used for communicating with an external host. By applying the technical scheme provided by the invention, the heating power consumption can be reduced, the fluctuation range of the heating temperature is reduced, the detection range of the temperature measuring resistor is improved, and the specific selection of the individual sensors in the gas sensor array on the heating temperature, the heating waveform and the heating voltage can be supported.
Description
Technical Field
The invention relates to the field of semiconductor integrated circuits, in particular to a programmable PWM micro-hotplate temperature control system.
Background
Along with the increasing urgency of the production and life for odor recognition, people pay more and more attention to the development of the electronic nose. The gas sensor in the electronic nose is of vital importance, and the properties of the gas sensor are closely related to the temperature. On one hand, the temperature affects the selectivity, response time and recovery time of the gas-sensitive resistor, and on the other hand, a large amount of power consumption is generated in the heating process.
The traditional micro-hotplate heating mode mostly adopts constant voltage heating, but the constant voltage heating generates additional unnecessary power consumption. In order to achieve lower power consumption applications, the heating regime of the micro-hotplate must be changed. Most current temperature control circuits adopt a pulse width modulation technology, and the on-off of a heating switch is controlled according to a temperature comparison result, so that the temperature control effect is realized. For example, document 1 (Li Wenwu, chen Jianan. Temperature control integrated circuit design for heating based on micro-hotplate [ J ]. Mechanical and electronic, 2021,39 (04): 23-27.) a temperature control circuit designed in the document performs temperature comparison at each system clock edge to determine whether to heat or not, and if the heating temperature is less than the target temperature, the heating is continued until it is greater than the target temperature. However, with further demands on the system power consumption, adjustments to the heating time and the measurement time are made and still regulated using PWM techniques during heating, rather than continuing to heat below the target temperature.
In temperature acquisition, some articles utilize ADCs to read heating temperatures. For example: in document 2 (Design interface circuits for a logic film heater for a gas sensor resistor), a 10-bit ADC is used to read the heating temperature. However, if a wide dynamic range is required, a high-precision ADC is required, and the high-precision ADC is complex and expensive to design. The resistance frequency conversion circuit has the advantages of simple design, high dynamic range, good linearity and the like. Many studies have utilized the resistance frequency conversion circuit to read the temperature, but only the high performance of the resistance frequency conversion circuit is focused, and the digital conversion of the square wave frequency output by the resistance frequency conversion circuit is neglected.
How to change the heating voltage and the PWM waveform flexibly according to different heating temperatures to reduce the power consumption of the system and reduce the fluctuation range of the heating temperature and simultaneously observe the heating temperature in real time is a technical problem to be solved urgently by technical staff in the field.
Disclosure of Invention
The invention aims to provide a programmable PWM micro-hotplate temperature control system which can reduce heating power consumption, reduce fluctuation range of heating temperature, improve detection range of a temperature measuring resistor and support specific selection of individual sensors in a gas sensor array on heating temperature, heating waveform and heating voltage.
The purpose of the invention is realized by the following technical scheme:
a programmable PWM micro-hotplate temperature control system comprising: the digital control module is connected with the temperature control circuit module, the reading circuit module and the IIC interface module; wherein:
the digital control module is communicated with external equipment through the IIC interface module, receives heating voltage input by the external equipment and information related to PWM waveform, and outputs selected heating voltage and generated PWM waveform signals; the digital control module also calculates a square wave period according to the count value of the square wave signal transmitted by the reading circuit module for the external equipment to read through the IIC interface module, and provides the external equipment to read through the IIC interface module according to the comparison result of the count value of the appointed state of the judge signal transmitted by the temperature control circuit and the threshold value, and receives the comparison result of the count value of the appointed state of the square wave period and/or the judge signal and the threshold value by the external equipment, and dynamically adjusts the heating voltage and/or the information related to the PWM waveform;
the temperature control circuit module receives the heating voltage and the PWM waveform signal selected by the digital control module, and the PWM waveform signal is used for controlling the working mode of the temperature control circuit module; working in a comparison mode, and obtaining a judge signal by comparing a reference resistor connected with the comparison circuit with the resistance value of a heating resistor on the micro-hotplate; determining whether the heating mode is started or not at present based on the judge signal and the PWM waveform signal, if so, heating the gas sensor by a heating resistor on a micro-heating plate according to the selected heating circuit, and adjusting the heating time through the PWM waveform signal; the judge signal represents a comparison result signal;
and the reading circuit module converts the resistance transformation of the temperature measuring resistor on the micro-heating plate of the appointed gas sensor connected with the reading circuit module into current transformation within the counting time output by the digital control module, converts the current transformation into a corresponding square wave signal for counting, and transmits the counting value of the square wave signal to the digital control module.
According to the technical scheme provided by the invention, the heating power consumption can be reduced, the fluctuation range of the heating temperature is reduced, and the portability is considered while the self-consistency, the universality and the flexibility are met; meanwhile, the system not only supports the temperature control of the arrayed micro-hotplate type gas sensor, but also is suitable for the temperature control of various gas sensor micro-hotplates with different optimal gas-sensitive response temperatures.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
FIG. 1 is a schematic diagram of a programmable PWM micro-hotplate temperature control system according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a programmable heating voltage provided by an embodiment of the present invention;
FIG. 3 is a waveform diagram of a PWM waveform implementation provided by an embodiment of the present invention;
FIG. 4 is a schematic diagram of a temperature control circuit module according to an embodiment of the present invention;
FIG. 5 is a schematic circuit diagram of a temperature control unit according to an embodiment of the present invention;
fig. 6 is a schematic diagram of a resistance-frequency conversion circuit according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without making any creative effort, shall fall within the protection scope of the present invention.
The terms that may be used herein are first described as follows:
the term "and/or" means that either or both can be achieved, for example, X and/or Y means that both cases include "X" or "Y" as well as three cases including "X and Y".
The terms "comprising," "including," "containing," "having," or other similar terms of meaning should be construed as non-exclusive inclusions. For example: including a feature (e.g., material, component, ingredient, carrier, formulation, material, dimension, part, component, mechanism, device, process, procedure, method, reaction condition, processing condition, parameter, algorithm, signal, data, product, or article of manufacture), is to be construed as including not only the particular feature explicitly listed but also other features not explicitly listed as such which are known in the art.
The following describes a programmable PWM micro-hotplate temperature control system provided by the present invention in detail. Details which are not described in detail in the embodiments of the invention belong to the prior art which is known to a person skilled in the art. Those not specifically mentioned in the examples of the present invention were carried out according to the conventional conditions in the art or conditions suggested by the manufacturer. The instruments used in the examples of the present invention are not indicated by manufacturers, and are all conventional products that can be obtained by commercial purchase.
As shown in fig. 1, a programmable PWM micro-hotplate temperature control system mainly includes: the digital control module is connected with the temperature control circuit module, the reading circuit module and the IIC interface module; wherein:
the digital control module is communicated with external equipment through the IIC interface module, receives heating voltage input by the external equipment and information related to PWM waveform, and outputs selected heating voltage and generated PWM waveform signals; the digital control module also calculates a square wave period according to the count value of the square wave signal transmitted by the reading circuit module for the external equipment to read through the IIC interface module, and provides the external equipment to read through the IIC interface module according to the comparison result of the count value of the appointed state of the judge (comparison result) signal transmitted by the temperature control circuit and the threshold value, and receives the comparison result of the count value of the appointed state of the square wave period and/or the judge signal and the threshold value by the external equipment, and dynamically adjusts the heating voltage and/or the information related to the PWM waveform;
the temperature control circuit module receives the heating voltage and the PWM waveform signal selected by the digital control module, and the PWM waveform signal is used for controlling the working mode of the temperature control circuit module; working in a comparison mode, and obtaining a judge signal by comparing a reference resistor connected with the comparison circuit with the resistance value of a heating resistor on the micro-hotplate; determining whether the heating mode is started or not at present based on the judge signal and the PWM waveform signal, if so, heating a heating resistor on a micro-heating plate of the corresponding gas sensor according to the selected heating circuit, and adjusting the heating time through the PWM waveform signal;
and the reading circuit module converts the resistance transformation of the temperature measuring resistor on the micro-heating plate of the appointed gas sensor connected with the reading circuit module into current transformation within the counting time output by the digital control module, converts the current transformation into a corresponding square wave signal for counting, and transmits the counting value of the square wave signal to the digital control module. It mainly comprises: the resistance-frequency conversion module and the resistance-frequency conversion control module are described in detail later.
In addition, the system further comprises: the power supply management module, the power-on reset module and the clock module; wherein:
and the power supply management module regulates the output voltage of the low dropout linear regulator according to the voltage selected by the decoder to provide the voltage required by the work for each module of the system.
The power-on reset module is connected with the digital control module and is used for realizing initialization before system work;
the clock module is connected with the digital control module and used for providing a system clock signal.
For ease of understanding, the following detailed description is directed to various portions of the system.
1. IIC interface module.
The IIC interface module is connected to the digital control module, and is configured to implement communication between the system and an external device (e.g., a host as shown in fig. 1), specifically, to receive a heating voltage and related configuration information that are written by the external device, and to read a value stored in a related register in the digital control module into the external device.
2. And a power management module.
In the embodiment of the invention, the power management module is respectively connected with the rest modules of the system and an external gas sensor array, each gas sensor in the gas sensor array comprises a gas sensitive material, a detection electrode and a micro-hotplate, the micro-hotplate provides required temperature for the reaction of the gas sensitive material and gas, and the power management module comprises a plurality of LDOs (low dropout regulators) and bandgaps (band gap references) and is used for providing required voltage for the modules connected with the power management module and the gas sensor array.
3. And a power-on reset module.
As shown in fig. 1, the power-on reset module is connected to the digital control module, and is configured to initialize the system before operation.
4. And a clock module.
As shown in fig. 1, a clock module is connected to the digital control module for providing a stable system clock signal.
5. And a digital control module.
In the embodiment of the invention, the digital control module is a core device, can realize the programmability of heating voltage and the programmability of PWM waveform signals by combining the IIC interface module, and is internally provided with a plurality of data registers for storing related data information in order to realize the programmability in a matching way; in addition, the digital control module is also provided with a self-checking module which can perform self-checking according to the current situation so as to determine whether the current heating voltage and/or the PWM waveform signal are proper or not. Mainly as follows:
1. and a data register.
In the embodiment of the present invention, the data register mainly includes:
and the first data register is connected with a judge port output by the temperature control circuit module and used for receiving a comparison result (judge) signal sent by the temperature control circuit module.
And the second data register is connected with a decoder used for realizing voltage selection in the digital control module and used for storing the heating voltage input by the external equipment and received by the IIC interface module.
And the third data register is connected with the reading circuit module and is used for storing the count value of the square wave signal, the period of the corresponding square wave signal can be known according to the count value, and the period value of the square wave signal is in direct proportion to the resistance value of the temperature measuring resistor.
The fourth data register is bidirectionally connected with the IIC interface module and is used for storing configuration information input by the external equipment and received by the IIC interface module and storing an internal data value read by the external equipment through the IIC interface module; wherein the configuration information includes: PWM waveform signal, counting time, system clock pulse counting value in the counting time for calculating square wave period, and signal for measuring temperature of specified gas sensor; the PWM waveform signal includes: a clock frequency division period and a frequency division clock period number occupied by a PWM waveform which is high and low respectively under the clock signal after frequency division; the internal data values include: and comparing the period of the square wave signal and the count value of the designated state of the judge signal with a threshold value, wherein if the count value of the designated state of the judge signal exceeds the threshold value, an error is indicated, and the comparison result of the count value and the threshold value is an error signal.
2. Programmability of the heating voltage.
In the embodiment of the invention, a decoder is arranged in the digital control module, and the digital control module and the IIC interface module jointly realize the programmability of the heating voltage; the decoder receives heating voltage input by external equipment through the IIC interface module, selects voltage by decoding the heating voltage into one-hot code output, and the power management module regulates the output voltage of the LDO according to the selected heating voltage to generate V heater (i.e., the selected heating voltage) and output to the temperature controlled circuit module.
3. The programmability of the PWM waveform signal is realized.
In the embodiment of the present invention, a PWM waveform generating module is disposed in the digital control module, and after power-on reset (realized by the power-on reset module), the IIC interface module receives a clock frequency division period of each temperature control circuit unit (the temperature control circuit unit is a unit structure of the temperature control circuit module, which will be described later), and a frequency division clock period number occupied when the PWM waveform is high and low respectively under the frequency-divided clock signal, and generates a corresponding PWM waveform signal, and transmits the PWM waveform signal to the temperature control circuit module and the first data register.
As shown in fig. 3, from top to bottom, the original clock, the divided clock, and the PWM waveform are plotted according to the number of divided clock cycles that the PWM waveform occupies when the divided clock signal is high and low, respectively. In actual use, the PWM waveform can be dynamically programmed as needed. On the premise of ensuring small temperature fluctuation amplitude, the PWM waveform duty ratio is improved as much as possible to reduce power consumption. The PWM waveform is high and the temperature control circuit measures (i.e., operates in a compare mode). By adopting the programmable PWM waveform implementation mode, the use of a register can be effectively saved, so that the chip area is reduced.
4. And a self-checking module.
The input end of the self-checking module is connected with the reading circuit module, the output end of the self-checking module is connected with the IIC interface module, a comparison result signal (Judge signal) from the temperature control circuit module is received, the historical working state of the Judge signal is recorded, and the historical working state of the Judge signal represents the comparison result of the partial pressure on the heating resistor and the partial pressure on the reference resistor; at the falling edge of each PWM signal, if the divided voltage on the heating resistor (Rmhp) is smaller than the divided voltage on the reference resistor (Rref), namely the heating temperature is smaller than the target temperature, at the moment, the judge signal is in a low level, the counting value is added with 1, and if the divided voltage on the heating resistor (Rmhp) is larger than the divided voltage on the reference resistor (Rref), namely the heating temperature is larger than the target temperature, the counting value is cleared with 0. The counting value is compared with a threshold value, if the counting value is larger than the threshold value (the size of the threshold value can be set according to actual conditions or experience), an error is indicated, and if the counting value is smaller than the threshold value, normal operation is indicated. And storing the comparison result into a fourth data storage register for the external equipment to read through the IIC interface module.
After reading the error signal through the IIC interface module, the external equipment can analyze the reason for generating the error signal, so that the heating voltage and/or the information related to the PWM waveform are/is dynamically adjusted.
6. And a temperature control circuit module.
In an embodiment of the present invention, the temperature control circuit module includes: a plurality of temperature control circuit units arranged in an array form, wherein each temperature control circuit unit is respectively connected with a reference resistor R ref And a heating resistor R on the micro-hotplate mhp 。
As shown in fig. 4, it is a main structure of the temperature control circuit module; as shown in fig. 5, is the main structure of a single temperature control circuit unit.
Each temperature control circuit unit is also bidirectionally connected to the digital control module, and as shown in fig. 5, the temperature control circuit unit has two input terminals for PWM waveform signals, receives the PWM waveform signals from the digital control module, and has a voltage input terminal for receiving the heating voltage selected by the digital control module, and an output terminal for outputting a judge signal to the digital control module. The main principle is as follows:
the temperature control circuit unit has two working modes, namely a heating mode and a comparison mode; the comparison mode is performed when the PWM waveform signal is at a high level.
During the comparison mode, the NMOS transistor is turned on, and two identical constant current sources simultaneously supply constant currents to the heating resistor and the reference resistor. Comparing the voltage on a heating resistor on the micro-heating plate corresponding to the gas sensor with the voltage on a reference resistor by using a comparator to generate a judge signal; the Judge signal and the PWM waveform signal are subjected to OR operation and then acted on a grid electrode of the PMOS.
If the voltage on the heating resistor is greater than the voltage on the reference resistor, the heating temperature is indicated to exceed the target temperature, and the Judge signal and the PWM waveform signal are subjected to OR operation to obtain a signal acting on the PMOS grid electrode, namely a high-level signal, and heating is not carried out.
If the voltage on the heating resistor is smaller than the voltage on the reference resistor, the heating temperature is smaller than the target temperature, and the Judge signal and the PWM waveform signal are subjected to OR operation, wherein the two conditions are as follows: in the first case, when the PWM waveform signal is at a high level at the present time, the signal acting on the PMOS gate obtained by the or operation is at a high level, and no heating is performed; in the first case, when the PWM waveform signal is at a low level at the present time, the signal acting on the gate of the PMOS transistor obtained by the or operation is at a low level, the PMOS transistor is turned on, and the selected heating voltage is applied to the heating resistor for heating.
In the heating period, the PWM waveform signal is modulated to a low level to continue heating, and the PWM waveform signal is modulated to a high level to stop heating.
Specifically, the above principle will be described below with reference to the circuit shown in fig. 5. As shown in FIG. 5, the two same constant current sources are connected by NMOS and V heater Connected byAnd a PMOS. In the comparison mode, the two NMOS tubes are both switched on, and the PMOS tube is switched off. The two NMOS tubes are conducted, so that two same constant current sources can simultaneously provide constant current for the heating resistor and the reference resistor. And comparing the voltage on the heating resistor with the voltage on the reference resistor by using a comparator. If the resistance R is heated mhp The upper voltage is greater than the reference resistance R ref And the upper voltage indicates that the heating temperature exceeds the target temperature, the input signal of the D end of the trigger is 1, and the D end signal of the trigger is synchronized to the Q end at the falling edge of the PWM waveform. The Q end signal of the trigger is the judge signal. The judge signal and the PWM signal are subjected to OR operation, and the output is the signal acting on the PMOS grid. The signal acting on the gate of the PMOS controls whether the PMOS is on at this time, i.e. whether it is heating up at this time. If the signal acting on the grid electrode of the PMOS is in a low level, the PMOS is turned on to heat, and if the signal acting on the grid electrode of the PMOS is in a high level, the PMOS is turned off to stop heating; as is clear from the above description, the signal acting on the PMOS gate is not only related to the judge signal but also related to the level of the PWM signal at that time. In the above process, if the judge signal is 1, the and PWM or operation is inevitably 1, and no heating is performed. If the voltage on the Rmhp is smaller than the voltage on the Rref, namely the heating temperature is smaller than the target temperature, the judge signal is 0 at the moment and is regulated by the PWM signal, if the PWM signal is high, the voltage is 1 after OR operation at the moment, heating is not carried out, and if the PWM signal is low, the voltage is 0 after OR operation at the moment, heating is carried out.
As will be understood by those skilled in the art, the resistance of the heating resistor is positively correlated with the heating temperature, and the resistance of the reference resistor is always the resistance of the heating resistor when heated to the target temperature, because both current sources are constant current sources, the comparison of the voltages across the heating resistor and the reference resistor is the comparison of their own resistors. The result of the comparison of the two resistances is the relationship between the reaction heating temperature and the target temperature.
7. And reading the circuit module.
In an embodiment of the present invention, the read circuit module includes: the resistance-frequency conversion module and the resistance-frequency conversion control module.
1. And a resistance-frequency conversion module.
And the resistance-frequency conversion module is used for reading the resistance value of the temperature measuring resistor Rt on the micro-hot plate of the specified gas sensor connected with the resistance-frequency conversion module according to the temperature measuring signal of the specified gas sensor written by the external equipment through the IIC interface module within the counting time, and converting the resistance value into a corresponding square wave signal. The counting time is written from an external device through an IIC interface, and the time for counting the square wave signals converted by the temperature measuring resistor is mainly set.
As shown in fig. 6, the resistance-frequency conversion module includes: the circuit comprises an operational amplifier, an MOS power tube, a current mirror circuit (a PMOS current mirror and an NMOS current mirror), an integrating capacitor C1, a hysteresis comparator and a shaping circuit.
The operational amplifier and the MOS power tube form a voltage-current conversion circuit, one end of the operational amplifier is a reference voltage, the other end of the operational amplifier is connected with the temperature measuring resistor, and a corresponding current value is output through the MOS power tube. Reference voltage V ref The voltage clamping is carried out by using the negative feedback circuit of the operational amplifier, so that the voltage applied to the temperature measuring resistor is constant, and the change of the temperature measuring resistor can be converted into the change of the current.
The current value is reduced by the current mirror circuit according to a set proportion (for example, 10.
And then, a triangular wave with specific frequency is formed by charging and discharging through the integrating capacitor C1, and the triangular wave is converted into a square wave signal by the hysteresis comparator and is output through the shaping circuit. The period of the square wave signal output by the resistance-frequency conversion circuit is in direct proportion to the resistance value of the temperature measuring resistor.
2. And a resistance-frequency conversion control module.
The resistance-frequency conversion control module is used for transmitting the counting time from the digital control module to the resistance-frequency conversion module, counting the square wave signals and converting the analog signals output by the resistance-frequency conversion module into digital signals.
The count value obtained by the resistance-frequency conversion control module is stored in a third data register of the digital control moduleThe digital control module calculates the period T of the square wave signal according to the count value rtf And stored in a fourth data register.
The calculation mode of the square wave signal period is as follows:
wherein, T rtf Is the period of the square wave signal, T ref Is the period of the system clock, N ref Is the system clock pulse count value N in the count time rtf Is a count value of the square wave signal at the count time.
Because of the square wave signal period T rtf The resistance value of the temperature measuring resistor is in direct proportion, so that the resistance value of the temperature measuring resistor can be calculated after the square wave signal period is obtained.
The resistance value of the temperature measuring resistor is proportional to T rtf ：
R t ∝T rtf
In addition, the heating resistor heats the environment, so that the temperature of the surrounding environment rises, the temperature measuring resistor measures the temperature in the environment at the moment, the temperature can also be regarded as the heating temperature, and after the square wave period is read by external equipment and is converted into the resistance value of the temperature measuring resistor, the resistance value can be compared with the reference resistor corresponding to the target temperature, and the information and/or the heating voltage related to the PWM waveform can be dynamically adjusted.
Compared with the prior art, the technical scheme of the embodiment of the invention has the following beneficial effects:
1) The programmable PWM micro-hotplate temperature control system provided by the invention is self-consistent and can work without any external experimental instrument. The system can be a system on chip and integrated on a chip, the chip can be manufactured based on the SMIC180nm standard CMOS process, and the area of the chip is less than 2mm 2 The gas sensor is integrated with the gas sensor, and the requirement of people on portability is met.
2) The invention can flexibly configure the duty ratio and the period of the heating voltage through the IIC interface circuit, and external equipment can read the square wave period converted by the temperature measuring resistor of the micro-hotplate in real time through the IIC interface, and after the square wave period is processed into a resistance value through the external equipment, the resistance value is compared with the reference resistor corresponding to the temperature measuring resistor and the target temperature, so that the heating voltage is selected and the waveform of the heating voltage is dynamically adjusted, thereby greatly reducing the power consumption and the fluctuation amplitude of the heating temperature.
3) The micro-hotplate temperature control system provided by the invention provides programmable heating voltage for the heating resistor, can be externally connected with different reference resistors, and can meet the temperature control requirements of various gas sensor micro-hotplates with different optimal gas-sensitive response temperatures. In addition, the response curves of the same gas sensor to the same concentration of gas at different temperatures are different, and the system also provides a way for characteristic expansion of odor recognition.
4) The micro-hotplate temperature control system provided by the invention can be used for all micro-hotplate type gas sensors and is not limited to MEMS MOS gas sensors. And because no external instrument is needed, the temperature control system can be directly connected with other systems for use, and has strong universality.
5) The system can support the specific selection of heating temperature, heating waveform and heating voltage for individual sensors in the gas sensor array. Along with the increasing urgency of production and life on the requirement of odor identification, the gas sensor array is more and more emphasized, so that higher requirements are provided for accurate and personalized temperature control of the arrayed gas sensor micro-hotplate.
It is obvious to those skilled in the art that, for convenience and simplicity of description, the above division of each functional module is only used for illustration, and in practical applications, the above function distribution may be completed by different functional modules according to needs, that is, the internal structure of the system is divided into different functional modules to complete all or part of the above described functions.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (9)
1. A programmable PWM micro-hotplate temperature control system, comprising: the digital control module is connected with the temperature control circuit module, the reading circuit module and the IIC interface module; wherein:
the digital control module is communicated with external equipment through the IIC interface module, receives heating voltage input by the external equipment and information related to PWM waveform, and outputs selected heating voltage and generated PWM waveform signals; the digital control module also calculates a square wave period according to the count value of the square wave signal transmitted by the reading circuit module for the external equipment to read through the IIC interface module, and provides the external equipment to read through the IIC interface module according to the comparison result of the count value of the appointed state of the judge signal transmitted by the temperature control circuit and the threshold value, and receives the comparison result of the count value of the appointed state of the square wave period and/or the judge signal and the threshold value by the external equipment, and dynamically adjusts the heating voltage and/or the information related to the PWM waveform;
the temperature control circuit module receives the heating voltage and the PWM waveform signal selected by the digital control module, and the PWM waveform signal is used for controlling the working mode of the temperature control circuit module; working in a comparison mode, and obtaining a judge signal by comparing a reference resistor connected with the comparison circuit with the resistance value of a heating resistor on the micro-hotplate; determining whether the heating mode is started or not at present based on the judge signal and the PWM waveform signal, if so, heating the gas sensor by a heating resistor on a micro-heating plate according to the selected heating circuit, and adjusting the heating time through the PWM waveform signal; the judge signal represents a comparison result signal;
the reading circuit module converts the resistance transformation of the temperature measuring resistor on the micro-hotplate of the designated gas sensor connected with the reading circuit module into current transformation within the counting time output by the digital control module, converts the current transformation into a corresponding square wave signal for counting, and transmits the counting value of the square wave signal to the digital control module;
the read circuit module includes: the resistance-frequency conversion module and the resistance-frequency conversion control module; wherein:
the resistance-frequency conversion module is used for reading the resistance value of the temperature measuring resistor on the micro-hotplate of the specified gas sensor connected with the resistance-frequency conversion module according to a signal which is written by external equipment through the IIC interface module and is used for measuring the temperature of the specified gas sensor within the counting time, and converting the signal into a corresponding square wave signal;
the resistance-frequency conversion control module is used for transmitting the counting time from the digital control module to the resistance-frequency conversion module and counting the square wave signals;
the digital control module calculates the period of the square wave signal according to the counting value, the period of the square wave signal is in direct proportion to the resistance value of the temperature measuring resistor, and the calculation formula of the period of the square wave signal is as follows:
wherein, T rtf Is the period of the square wave signal, T ref Is the period of the system clock, N tef Is the system clock pulse count value N in the count time rtf Is a count value of the square wave signal at the count time.
2. The programmable PWM micro-hotplate temperature control system according to claim 1, wherein the digital control module in combination with the IIC interface module realizes programmability of PWM waveform signals, comprising: and the digital control module is internally provided with a PWM waveform generation module, receives the clock frequency division period through the IIC interface module after power-on reset, and generates corresponding PWM waveform signals according to the frequency division clock period number occupied by the PWM waveform when the PWM waveform is high and low respectively under the clock signals after frequency division, and transmits the PWM waveform signals to the temperature control circuit module.
3. The programmable PWM micro-hotplate temperature control system according to claim 1 or 2, wherein the temperature control circuit module comprises: the temperature control circuit units are distributed in an array form, and each temperature control circuit unit is respectively connected with a reference resistor and a heating resistor on a micro-heating plate of the gas sensor;
each temperature control circuit unit receives a corresponding PWM waveform signal, when the PWM waveform signal is at a high level, the corresponding temperature control circuit unit works in a comparison mode, and during the comparison mode, a comparator is used for comparing the voltage on a heating resistor on a micro-heating plate of the specified gas sensor with the voltage on a reference resistor to generate a judge signal; performing OR operation on the judge signal and the PWM waveform signal;
if the voltage on the heating resistor is greater than the voltage on the reference resistor, the heating temperature is indicated to exceed the target temperature, or operation is carried out on the judge signal and the PWM waveform signal, the obtained signal is high level, and heating is not carried out;
if the voltage on the heating resistor is smaller than the voltage on the reference resistor, the heating temperature is smaller than the target temperature, and the Judge signal and the PWM waveform signal are subjected to OR operation, wherein the two conditions are as follows: in the first case, if the PWM waveform signal at the current time is at a high level, the signal obtained by or operation is at a high level, and no heating is performed; in the second case, if the PWM waveform signal at the present time is at a low level, the signal obtained by or operation is at a low level, and the selected heating voltage is applied to the heating resistor for heating;
in the heating period, the PWM waveform signal is modulated to a low level to continue heating, and the PWM waveform signal is modulated to a high level to stop heating.
4. The programmable PWM micro-hotplate temperature control system according to claim 1, wherein the resistance-frequency conversion module comprises: the circuit comprises an operational amplifier, an MOS power tube, a current mirror circuit, an integrating capacitor, a hysteresis comparator and a shaping circuit;
the operational amplifier and the MOS power tube form a voltage-current conversion circuit, one end of the operational amplifier is a reference voltage, the other end of the operational amplifier is connected with a temperature measuring resistor, and a corresponding current value is output through the MOS power tube; and after the current value is reduced by the current mirror circuit according to a set proportion, a triangular waveform is formed by the integrating capacitor, and the triangular waveform is converted into a square wave signal by the hysteresis comparator and is output by the shaping circuit.
5. The programmable PWM micro-hotplate temperature control system according to claim 1, wherein a decoder is arranged inside the digital control module, and programmability of a heating voltage is realized together with the IIC interface module; the decoder receives heating voltage input by external equipment through the IIC interface module, and selects the voltage by decoding the heating voltage into one-hot codes to be output.
6. A programmable PWM micro-hotplate temperature control system according to claim 1 or 5, characterized in that the system further comprises: the power supply management module adjusts the output voltage of the low dropout linear regulator according to the heating voltage selected by the decoder in the digital control module and provides the voltage required by the work for each module of the system;
the power management module is also connected with an external gas sensor array to provide the external gas sensor array with voltage required by work.
7. The programmable PWM micro-hotplate temperature control system according to claim 1, wherein the digital control module is provided with a plurality of data registers; wherein:
the first data register is connected with a judge port output by the temperature control circuit module and used for receiving a judge signal sent by the temperature control circuit module;
the second data register is connected with a decoder used for realizing voltage selection in the digital control module and used for storing the heating voltage input by the external equipment received by the IIC interface module;
the third data register is connected with the reading circuit module and used for storing the count value of the square wave signal;
the fourth data register is bidirectionally connected with the IIC interface module and is used for storing configuration information input by the external equipment and received by the IIC interface module and storing an internal data value read by the external equipment through the IIC interface module; wherein:
the configuration information includes: PWM waveform signal, counting time, system clock pulse counting value in the counting time for calculating square wave period, and signal for measuring temperature of specified gas sensor; the PWM waveform signal includes: a clock frequency division period, and a frequency division clock period number occupied by a PWM waveform when the PWM waveform is high and low respectively under the clock signal after frequency division; the internal data values include: and comparing the period of the square wave signal and the count value of the appointed state of the judge signal with a threshold value, wherein if the count value of the appointed state of the judge signal exceeds the threshold value, an error is indicated, and the comparison result of the count value and the threshold value is an error signal.
8. The programmable PWM micro-hotplate temperature control system according to claim 1, wherein the digital control module is provided with a self-checking module, the self-checking module receives a judge signal from the temperature control circuit module and records a historical working state of the judge signal, and the historical working state of the judge signal indicates whether the digital control module works in a heating mode or not; if the divided voltage on the heating resistor is smaller than the divided voltage on the reference resistor at the falling edge of each PWM waveform signal, the heating temperature is smaller than the target temperature, namely the judge signal is at low level, the count value is increased by 1, and if the divided voltage on the heating resistor is larger than the divided voltage on the reference resistor, the heating temperature is larger than the target temperature, the count value is clear by 0; comparing the count value with a threshold value, if the count value is greater than the threshold value, indicating that an error occurs, and if the count value is less than the threshold value, indicating that the work is normal; and storing the comparison result of the count value and the threshold value into a corresponding data storage register for the external equipment to read through the IIC interface module.
9. The programmable PWM micro-hotplate temperature control system according to claim 1, wherein the power-on reset module and the clock module; wherein:
the power-on reset module is connected with the digital control module and is used for realizing initialization before system work;
the clock module is connected with the digital control module and used for providing a system clock signal.
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| CN105652919B (en) * | 2014-11-21 | 2018-02-02 | 深圳市科曼医疗设备有限公司 | Temperature control system |
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| CN209982742U (en) * | 2019-01-31 | 2020-01-21 | 宁波大学 | Temperature control heating system based on three-wire system thermal resistor |
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