Electrically heated devices and methods for operating heaters

Abstract

An electrothermal based device comprising a heater (11), a readout circuit (14), a digital controller (16) and a digital sigma-delta modulator (19), wherein a first input (17) of the digital controller is coupled to a first output (18) of the readout circuit (14), a first input (20) of the digital sigma-delta modulator is coupled to an output (21) of the digital controller (16) and an output (22) of the digital sigma-delta modulator is coupled to the heater (11).

Description

[0001] The present disclosure relates to an electrothermal based device, an apparatus including the electrothermal based device, and a method for operating a heater in the electrothermal based device.

[0002] An electrothermal based device (referred to as a device) typically includes a heater and a control circuit that controls the current flowing through the heater. The device is typically implemented as a micro-electromechanical system device (referred to as a MEMS device). The heater may be used to heat a gas sensing material, to emit infrared radiation, or for other purposes.

[0003] An object is to provide an electrothermal based device, an arrangement comprising the electrothermal based device and a method for operating a heater in an electrothermal based device with improved heater control.

[0004] These objects are achieved by the subject matter of the independent claims. Further developments and embodiments are described in the dependent claims.

[0005] In one embodiment, an electrothermal based device includes a heater, a readout circuit, a digital controller, and a digital sigma-delta modulator, wherein a first input of the digital controller is coupled to a first output of the readout circuit, a first input of the digital sigma-delta modulator is coupled to an output of the digital controller and an output of the digital sigma-delta modulator is coupled to the heater.

[0006] Advantageously, the heater is driven by pulses of a digital sigma-delta modulator and therefore receives a precise amount of electrical power to keep the temperature of the heater constant.

[0007] In one embodiment, the electrothermal-based device is implemented as a gas sensor or a gas sensor array. Chemical processes (such as absorption, adsorption, or chemical reactions) depend on the temperature of the reactants. Therefore, accurate control of the temperature of one or more gas sensors is useful for accurate measurement. The one or more gases to be detected can be oxidizing gases, reducing gases, combustible gases, humidity, or other gases. For example, the electrothermal-based device can detect ethanol, toluene, nitrogen dioxide, ozone, methane, hydrogen, carbon monoxide, or can be sensitive to a variety of volatile organic compounds (abbreviated as VOCs).

[0008] In one embodiment, the electrothermal based device is implemented as a resistive gas sensor or a calorimetric gas sensor. The electrothermal based device may include a sensing material thermally coupled to a heater. The sensing material interacts with the gas to be detected. Advantageously, the use of an appropriate sensing material results in high sensitivity and selectivity for gas measurement.

[0009] In one embodiment, the electrothermal based device is a thermal conductivity sensor. The thermal conductivity sensor is designed to measure the thermal conductivity of a sample. Advantageously, since different gases have different thermal conductivities, the gas concentration in the sample can be detected. For example, in the case of a binary mixture of two gases, the thermal conductivity sensor can determine the ratio of the two gases. For example, the ratio of the two gases can be determined in devices in the process industry. The thermal conductivity sensor can be free of sensing material. Advantageously, aging or drift phenomena that may be caused by the sensing material can be avoided.

[0010] In one embodiment, the electrothermal based device is implemented as an infrared emitter (abbreviated as IR emitter). The heater is configured as an infrared radiation emitter. Advantageously, the electrothermal based device emits infrared radiation without the use of compound semiconductors (such as III-V compound semiconductors). Advantageously, the electrothermal based device can include a silicon substrate and can be manufactured by silicon processing. Infrared is abbreviated as IR.

[0011] In one embodiment, the electrothermal based device is implemented as an optical gas sensor or a photoacoustic gas sensor. The heater is implemented as an IR radiation emitter. The electrothermal based device comprises a sensor element or a detector.

[0012] In another refinement, where the electrothermal based device is an optical gas sensor, the detector may be an optical detector such as an IR detector. The heater is coupled to the optical detector via an optical path. Gases in the optical path that absorb IR radiation can be detected by measuring the IR radiation detected by the optical detector. The optical gas sensor detects gas by detecting absorption of infrared wavelengths that are specific to the gas. By optically filtering the IR radiation emitted by the heater, the IR radiation spectrum is limited to the absorption band of the gas to be detected.

[0013] In another refinement, where the electrothermal based device is a photoacoustic gas sensor, the sensor element may be a microphone or a pressure sensor. A sample container or chamber encloses a gas sample, a heater acting as an IR emitter, and a microphone or a pressure sensor. The gas in the gas sample that absorbs IR radiation is heated and can therefore be detected by the microphone or the pressure sensor. Typically, the IR radiation emitted by the heater is modulated or chopped with a frequency that can be detected by the microphone or the pressure sensor. The device includes a filter for selecting a suitable wavelength of IR radiation. The apparatus may include a pump and at least one valve coupled to the sample container or chamber for changing the gas sample.

[0014] In one embodiment, the electrothermal based device is a micro-electromechanical system device (MEMS device for short). The MEMS device includes a membrane (such as a dielectric membrane). Typically, one or more dielectric layers are supported on a semiconductor substrate. The substrate has an etched portion, and a portion of the dielectric adjacent to the etched portion of the substrate can be considered as a dielectric membrane. The heater can be embedded in the membrane or can be above or below the membrane. Advantageously, by arranging the heater in or on the membrane, low thermal conduction and therefore low power consumption can be maintained.

[0015] In one embodiment, the readout circuit generates a readout signal at a first output of the readout circuit. The readout signal depends on the heater resistance. Advantageously, the readout signal depends on the temperature of the heater and can be used for temperature measurement.

[0016] In one embodiment, the digital controller comprises a second input for receiving a target signal. The digital controller generates a control signal based on the readout signal and the target signal and provides the control signal to the first input of the digital sigma-delta modulator. Advantageously, the resistance value of the heater can be set by the target signal. The target signal can be constant or can be different in different operating phases of the device. The target signal can be a digital signal.

[0017] In one embodiment, a digital sigma-delta modulator generates a modulator output signal. Advantageously, the spectrum of the modulator output signal has low amplitude values ​​in the audible frequency range. The current flowing through the heater or the voltage provided to the heater may be consistent with the modulator output signal or may be set according to the modulator output signal.

[0018] In one embodiment, the digital sigma-delta modulator includes a second input for receiving a pause signal. When the pause signal has a first value, the digital sigma-delta modulator generates a modulator output signal having a constant value (e.g., a zero value). When the pause signal has a second value, the digital sigma-delta modulator generates a modulator output signal whose value depends on a control signal provided to the digital sigma-delta modulator. Advantageously, when the pause signal has a first value, the resistance value of the heater can be measured with high accuracy.

[0019] In one embodiment, the digital sigma-delta modulator includes a sigma-delta modulator circuit and a power buffer. The input of the sigma-delta modulator circuit is connected to a first input of the digital sigma-delta modulator. The power buffer includes an input connected to the output of the sigma-delta modulator circuit and an output connected to the output of the digital sigma-delta modulator for providing a modulator output signal. The power buffer includes a control input connected to the second input of the digital sigma-delta modulator. Advantageously, the logic function and the supply function of the digital sigma-delta modulator are separated into two circuit parts. Advantageously, the sigma-delta modulator circuit generates an internal signal and a circuit signal having a standard value of the logic circuit, and the power buffer generates a modulator output signal, the value of which is suitable for providing to the heater.

[0020] In one embodiment, the readout circuit includes a second output coupled to a second input of the digital sigma-delta modulator. The readout circuit generates a pause signal. When the pause signal has a first value, the readout circuit determines the readout signal. Advantageously, interference between the readout circuit and the digital sigma-delta modulator is avoided.

[0021] In one embodiment, the heater is electrically coupled to a readout circuit. The readout circuit generates a readout signal based on the resistance value of the heater. Advantageously, the device has no temperature sensor.

[0022] In one embodiment, the digital controller is implemented as a proportional-integral-derivative (PID) digital controller or a proportional-integral (PI) digital controller. Advantageously, by selecting appropriate parameters of the PID or PI digital controller, the resistance value of the heater is quickly adjusted to a predetermined value.

[0023] In one embodiment, a device includes the electrothermal based device. The device is implemented as one of the following: a mobile device, an indoor air monitor, an outdoor air monitor, an automotive air monitor, and an industrial air or gas monitor.

[0024] In one embodiment, a method for operating a heater in an electrothermal based device comprises:

[0025] - providing the modulator output signal to the heater in response to a control signal by digital sigma-delta modulation or a signal derived from the modulator output signal,

[0026] - generating a readout signal by a readout circuit, and

[0027] - generating a control signal based on the read signal.

[0028] In one embodiment, the readout signal is generated according to the resistance value of the heater.Thus, the heater is used for heating and for temperature measurement.

[0029] In one embodiment, the modulator output signal is implemented as a digital signal, such as a pulse signal or a bit stream signal. In one embodiment, the readout signal and the control signal are implemented as digital signals. The use of digital signals allows implementation by low power consumption digital circuits.

[0030] For example, the method of operating a heater in an electrothermal based device may be implemented by an electrothermal based device according to one of the embodiments defined above. The method of operating a heater in an electrothermal based device may for example be implemented as a method for gas measurement and / or a method for emitting IR radiation.

[0031] In one embodiment, an electrothermal based device enables closed loop heater control for gas sensing applications.

[0032] In one embodiment, the module comprises a heater.The module can be implemented as a gas sensor module or / and an off-chip module.

[0033] In one embodiment, the sensitivity of the gas sensor module including the heater is directly related to the temperature of the gas sensor module, so it is advantageous to keep the temperature constant. The electrothermal-based device maintains low power consumption, so the driving method used does not have high power consumption. Depending on the sensor used, a specific temperature distribution can be applied to the sensor; therefore, a fast response time is an advantage. The closed loop architecture of the electrothermal-based device is suitable for this purpose. The gas sensor module senses one or more gases by using a resistive gas sensor.

[0034] In one embodiment, a feedback control for a heater includes a sigma-delta drive for the heater, a resistance readout circuit, and a digital controller configured such that the total power provided by the sigma-delta drive is set by an externally provided set point value and a measured heater resistance. The heater bias is turned off to measure the heater resistance.

[0035] In one embodiment, the feedback control system is implemented such that the heater is part of the gas sensor.

[0036] In one embodiment, the feedback control system is implemented such that the heater is an IR emitter.

[0037] Advantageously, a sigma-delta drive method is used to drive the heater. Furthermore, temperature feedback is provided by using the heater itself; this results in lower thermal power consumption and also allows for fewer bond pads on the device.

[0038] The electrothermal based device performs loop processing: Full digital processing is used with the PID algorithm. A digital sigma-delta modulator driven by a digital character is used as a power driver. Advantageously, the gas sensor adopts the sigma-delta drive method. The control loop for the heater uses the sigma-delta drive method and the heater itself is used as a temperature sensor.

[0039] The type and concept of thermal sensors are advantageous because the resistance of the heater is sensed by applying a current and reading a voltage. The heater acts as a temperature sensor. The resistance of the heater is linked to the temperature of the heater by characterization. Therefore, the device can be without a dedicated temperature sensor, which can be a thermocouple, a resistance temperature detector (abbreviated as RTD), or other sensor. Therefore, the complexity of the sensor module is reduced.

[0040] Power consumption is low and flexibility is high, since the device uses fully digital processing; the analog readout circuitry can remain powered off in most situations; and the PID controller is operated only at fixed intervals while it calculates a new power level. Power efficiency and temperature stability are high: the pulsed output driven by the sigma-delta driver results in low power consumption and the ability to vary the heating power with high resolution. The temperature ripple is much lower than that obtained with, for example, a pulse width modulation driver (PWM driver for short). The emission level is favorable: the sigma-delta driver distributes the emission over a wide spectrum, compared to a PWM driver that concentrates the emission in lines at multiples of the PWM frequency.

[0041] In one embodiment, a circuit or device includes a gas sensor module including a heater and a resistive sensing material, a resistive readout circuit, a digital PID controller, a digital sigma-delta modulator, and a clock generator.

[0042] In one embodiment, the apparatus is configured such that the temperature of the heater is 50°C to 600°C, alternatively 100°C to 550°C, alternatively 200°C to 500°C, or alternatively 300°C to 400°C.

[0043] The relationship between heater resistance and heater temperature is known, so the target temperature can be specified in terms of resistance value. The PID controller compares the target resistance value to the actual heater resistance obtained from the resistance table; it then takes into account the current error and error history to generate the desired power level. The sigma-delta modulator converts the multi-bit power level into a high-frequency bit stream; the power level information is encoded as the pulse density in the bit stream. The sigma-delta modulator is coupled to a clock that can be independent of the system clock. The bit stream is applied directly to the heater; then, depending on the bit value, the power value applied to the heater is zero or maximum (VDD 2 / RHeater); the heating efficiency is very high because the only loss is through the on-resistance of the power driver (i.e. very low). RHeater is the resistance value of the heater and VDD is the value of the supply voltage.

[0044] After the system clock pulse, a pause signal is generated to pause the power supply to the heater for the time required to acquire the heater resistance. To sense the heater resistance, a DC method is used: the resistance of the heater is measured by applying a known current and acquiring the resulting voltage or by applying a known voltage and acquiring the resulting current. The loop is then closed on the input of the PID controller. After the thermal loop has reached equilibrium, the gas sensor itself can be measured; the value of the sensor resistance depends on the temperature and the gas concentration.

[0045] To enhance gas selectivity and improve sensor accuracy, a specific temperature profile is imposed in time by varying the target assigned to the PID controller while performing multiple sensor readings at specific points in the temperature profile.

[0046] A variation or alternative to the described design or operation may be to arrange multiple sensors and heaters in the same module (e.g., a gas sensor module), each module having its own temperature control loop. The heater resistance is measured while power is applied to the heater (i.e., without turning off the power driver). The module is built directly on the integrated circuit using a membrane grown above the silicon but separated by an air gap. The module (including the heater and sensing material) is manufactured on the same chip as the integrated circuit. The heater can be a resistive heater or a metal oxide semiconductor field effect transistor (MOSFET for short). The control loop can be external to the sensor package.

[0047] Electrothermal based devices allow for flexible, precise and efficient temperature control of the modules.

[0048] The following description of the embodiment drawings may further illustrate and explain aspects of an electrothermal-based device, an apparatus including an electrothermal-based device, and a method for operating a heater in an electrothermal-based device. Devices and circuit parts having the same structure and the same effect are represented by equivalent reference numerals, respectively. As long as the functional aspects of the devices or circuit parts in different figures correspond to each other, their description will not be repeated for each of the subsequent figures.

[0049] Figure 1A and 1B An example of an electrothermal based device is shown;

[0050] Figures 2A to 2C An example of a module for an electrothermal based device is shown;

[0051] Figure 3A and 3B An example of the characteristics of an electrothermal based device is shown;

[0052] Figure 4A and 4B An example of the characteristics of another electrothermal based device is shown;

[0053] Figures 5A to 5D Other examples of electrothermal based devices are shown; and

[0054] Fig. 6A and 6B An example of an apparatus having an electrothermal based device is shown.

[0055] Figure 1A An example of an electrothermal-based device 10 (referred to as a device for short) is shown. The device 10 includes a heater 11. The heater 11 is implemented as a resistive heater. The heater 11 has a first terminal 12 and a second terminal 13. The material of the heater 11 may be a metal (such as platinum, gold, nickel, copper, molybdenum, aluminum, tungsten, or titanium), a mixture of metals, a semiconductor (such as polycrystalline silicon or single crystal silicon), or a silicide.

[0056] In addition, the device 10 includes a readout circuit 14. The readout circuit 14 is coupled to the heater 11. For example, an input 15 of the readout circuit 14 is connected to the first terminal 12 of the heater 11. The input 15 of the readout circuit 14 can be directly and permanently connected to the first terminal 12 of the heater 11. Additionally, the device 10 includes a digital controller 16. The digital controller 16 includes a first input 17 coupled to a first output 18 of the readout circuit 14. The first input 17 of the digital controller 16 is a digital input. The first output 18 of the readout circuit 14 is a digital output. The first input 17 of the digital controller 16 can be directly and permanently connected to the first output 18 of the readout circuit 14. The digital controller 16 has a second input 28. The second input 28 of the digital controller 16 is a digital input. The digital controller 16 is implemented as a proportional-integral-derivative digital controller (abbreviated as PID controller). Alternatively, the digital controller 16 is implemented as a proportional-integral digital controller (abbreviated as PI controller).

[0057] Additionally, the device 10 includes a digital sigma-delta modulator 19 (modulator for short). A first input 20 of the modulator 19 is coupled to an output 21 of the digital controller 16. The first input 20 of the modulator 19 is a digital input. The output 21 of the digital controller 16 is a digital output. The first input 20 of the modulator 19 may be directly and permanently connected to the output 21 of the digital controller 16. The output 22 of the modulator 19 is coupled to the heater 11. For example, the output 22 of the modulator 19 is connected to the first terminal 12 of the heater 11. The output 22 of the modulator 19 may be directly and permanently connected to the first terminal 12 of the heater 11. The digital sigma-delta modulator 19 can also be referred to as a digital delta-sigma modulator.

[0058] Furthermore, the device 10 comprises a system clock 23. An output of the system clock 23 is coupled to a clock input 24 of the digital controller 16. Another output of the system clock 23 is coupled to a clock input 25 of the readout circuit 14.

[0059] The readout circuit 14 is implemented as a resistance meter. The readout circuit 14 includes an analog-to-digital converter 30 (AD converter for short). The output of the AD converter 30 is connected to a first output 18 of the readout circuit 14. In addition, the readout circuit 14 includes a sample-and-hold circuit 31, the output of which is connected to the input of the AD converter 30. The readout circuit 14 includes an analog front-end circuit 32, which is coupled to the input 15 of the readout circuit 14 on its input side. The input of the analog front-end circuit 32 is directly and permanently connected to the first terminal 12 of the heater 11. The output of the analog front-end 32 is coupled to the AD converter 30 via the sample-and-hold circuit 31. The readout circuit 14 includes a second output 26 coupled to a second input 27 of the modulator 19. The readout circuit 14 is implemented as a resistance meter for measuring the resistance of the heater 11.

[0060] The device 10 comprises a module 40. The module 40 comprises a heater 11. The module 40 may be implemented as a gas sensor module. The module 40 may comprise a sensor element 41. The sensor element 41 may be implemented as a sensitive resistor, for example.

[0061] The readout circuit 14 generates a readout signal SR at a first output 18 of the readout circuit 14. The readout signal SR is provided to a first input 17 of a digital controller 16. The digital controller 16 receives a target signal ST at a second input 28. The digital controller 16 generates a control signal SC at an output 21 of the digital controller 16. The control signal SC is provided to a first input 20 of a modulator 19. The control signal SC depends on the target signal ST and the readout signal SR. The control signal SC is generated by using a PI or PID algorithm. For example, the control signal SC may depend on the difference between the target signal ST and the readout signal SR.

[0062] The modulator 19 generates a modulator output signal SM at an output 22 of the modulator 19. The modulator output signal SM is applied to the heater 11. The modulator output signal SM is implemented as a current or a voltage. According to the parameters of the heater 11, a readout signal SR is generated by the readout circuit 14. The readout signal SR may depend on the resistance value of the heater 11. Since the resistance value 11 of the heater 11 depends on the temperature of the heater 11, the readout signal SR depends on the temperature of the heater 11. Therefore, the readout signal SR can be implemented as a temperature measurement signal. The closed loop includes the heater 11, the readout circuit 14, the digital controller 16 and the modulator 19. By using this loop, the resistance value of the heater 11 can be set according to the target signal ST.

[0063] The modulator 19 receives a pause signal SP at a second input 27 of the modulator 19. When the pause signal SP has a first value, the modulator 19 generates a modulator output signal SM having a constant value (e.g., 0V or 0A). In addition, when the pause signal SP has a second value, the modulator 19 will generate a modulator output signal SM according to the control signal SC. The modulator output signal SM can have the form of a bit stream. The modulator output signal SM can obtain only two voltage values, namely a voltage value of 0V and a first voltage value, or only two current values, such as a current value of 0A or a first current value I1. The first voltage value can, for example, be equal to the value of the power supply voltage VDD. The first current value I1 can be approximately equal to VDD / RHeater, where RHeater is the resistance value of the heater 11.

[0064] The system clock 23 generates a clock signal SO1 which is applied to a clock input 25 of the readout circuit 14. In addition, the system clock 23 generates another clock signal SO2 which is provided to a clock input 24 of the digital controller 16. The first clock signal SO1 and the second clock signal SO2 may be equal.

[0065] Advantageously, the device 10 provides for precise control of the temperature of the heater 11 .

[0066] In an alternative embodiment not shown, the module 40 is devoid of the sensor element 41. The heater 11 may be implemented as an infrared radiation emitter (IR emitter for short).

[0067] Figure 1B Another example of device 10 is shown, which is Figure 1A . The modulator 19 includes a power buffer 50. The power buffer 50 forms the output of the sigma-delta modulator 19. The output of the power buffer 50 is connected to the output 22 of the modulator 19. The output of the power buffer 50 can be directly and permanently connected to the first terminal 12 of the heater 11. The second terminal 13 of the heater 11 is connected to the reference potential terminal 59. The circuits of the device 10 (such as the readout circuit 14, the digital controller 16 and the modulator 19) can also be connected to the reference potential terminal 59 by connections not shown.

[0068] Furthermore, the modulator 19 comprises a sigma-delta modulator circuit 51 which is connected on its input side to a first input 20 of the modulator 19. An output of the sigma-delta modulator circuit 51 is connected to an input of a power buffer 50. A second input 27 of the modulator 19 is connected to a control input 53 of the power buffer 50. Thus, a second output 26 of the readout circuit 14 is connected to a control input 53 of the power buffer 50.

[0069] The sigma-delta modulator circuit 51 generates a circuit signal SCI in dependence on the control signal SC. The circuit signal SCI is provided to the input of the power buffer 50. The circuit signal SCI is generated independently of the value of the pause signal SP. The power buffer 50 provides a modulator output signal SM. In the case where the pause signal SP has a first value, the power buffer 50 generates a modulator output signal SM having a constant value. The constant value may be, for example, 0V or 0A. When the pause signal SP has a first value, the modulator output signal SM is independent of the circuit signal SCI. Only in the case where the pause signal SP has a second value, the power buffer 50 generates the modulator output signal SM in dependence on the circuit signal SCI.

[0070] The readout circuit 14 includes a logic circuit 55 connected to the clock input 25 of the readout circuit 14 on its input side and to the second output 26 of the readout circuit 14 on its output side. In addition, the logic circuit 55 can be connected to at least one of the AD converter 30, the sample and hold circuit 31, and the analog front end circuit 32. The logic circuit 55 generates a pause signal SP. The analog front end circuit 32 is implemented so that it can measure the resistance value of the heater 11. The first terminal 12 of the heater 11 is connected to the input of the analog front end circuit 32. For example, the analog front end circuit 32 may include a current source 33, the output of which is coupled to the input of the analog front end circuit 32. The output of the current source 33 may be connected to the first terminal 12 of the heater 11. The analog front end circuit 32 may include an amplifier 34, the input of which is coupled to the input of the analog front end circuit 32. The output of the amplifier 34 is coupled to the output of the analog front end circuit 32.

[0071] The analog front end circuit 32 is configured to supply current to the heater 11 and measure the voltage value at the first terminal 12 of the heater 11. The voltage or a signal derived from the voltage is supplied to the AD converter 30 via the sample and hold circuit 31. The current source 33 applies current to the heater 11. The current flows from the current source 33 to the reference potential terminal 59 via the heater 11. The voltage at the first terminal 12 is amplified by the amplifier 34. The amplified voltage generated by the amplifier 34 is applied to the AD converter 30 via the sample and hold circuit 31.

[0072] Alternatively, the analog front end circuit 32 is configured to supply a voltage and measure a current flowing to the heater 11. The current or a signal derived from the current is supplied to the AD converter 30 via the sample-and-hold circuit 31.

[0073] When the pause signal SP has a first value, the analog front end circuit 32 operates, and when the pause signal SP has a second value, the analog front end circuit does not operate. When the pause signal SP has a first value, the current source 33 provides current to the heater 11. Alternatively, when the pause signal SP has a second value, the current source 33 can be turned off and can not provide current. The current source 33 can be controlled, for example, by the pause signal SP. In an example, the current source 33 and the power buffer 50 operate asynchronously. The current value provided by the current source 33 can be lower than the current value provided by the modulator 19.

[0074] The sensor element 41 is connected to a sensor evaluation circuit 56 of the device 10. Furthermore, the device 10 comprises a control circuit 57 which is connected on its output side to the second input 28 of the digital controller 16. The sensor evaluation circuit 56 is coupled to the control circuit 57. The control circuit 57 can be implemented as a microprocessor, a microcontroller or a state machine.

[0075] The control circuit 57 generates a target signal ST. The control circuit 57 thus sets the resistance value and thus also the temperature of the heater 11. The control circuit 57 has an interface to provide data to other circuits outside the device 10 and to receive data from other circuits outside the device 10. The sensor evaluation circuit 56 generates a sensor signal SE as a function of the parameters of the sensor element 41. The sensor signal SE is provided to the control circuit 57.

[0076] Device 10 may include integrated circuit 58. Readout circuit 14, digital controller 16 and modulator 19 are integrated on a first surface of integrated circuit 58. At least one of sensor evaluation circuit 56, system clock 23 and control circuit 57 may optionally be integrated on a first surface of integrated circuit 58.

[0077] Thus, device 10 is implemented by using at least two semiconductor bodies: one semiconductor body includes integrated circuit 58, and another semiconductor body includes module 40. Device 10 may be implemented by using exactly two semiconductor bodies. Thus, module 40 may be referred to as an off-chip module.

[0078] Advantageously, closed loop control can be achieved by using a readout circuit 14 for temperature determination, a heater 11 and a digital controller 16. The loop can work with analog or digital values ​​or a combination of both. The advantage of a digital or semi-digital implementation is that the loop can be flexibly tuned even at run time and even when environmental conditions vary greatly; the digital controller 16 can take the form of a PI or PID type. Since all elements do not work continuously, power consumption is reduced.

[0079] As for the heating method, both linear and pulse drive can be used. Pulse drive takes advantage of the longer thermal inertia of the heater 11 plus the sensor 41, so that the required power is achieved as the average value of the pulses applied to the heater 11. Since the power is applied directly to the heater 11 in each pulse, the efficiency is very high, except for the low voltage drop caused by the MOS switch (which can be part of the power buffer 50).

[0080] The heater 11 itself can also be used as a temperature sensor. However, when using the pulse drive mode, temperature measurements can only be made when the heater 11 is not biased. The flow of the high current I through the heater 11 can be interrupted by using a pause signal SP.

[0081] A power buffer 50 included in the sigma-delta modulator 19 converts the logic level of the bit stream to a level that may be different from the digital cell power supply. To keep things simple, the level of the modulator output signal SM provided by the power buffer 50 is typically the power supply voltage VDD. Components such as the power buffer 50 are sized to handle the current I=VDD / RHeater, where RHeater is the resistance value of the heater 11. Whenever a resistance measurement is performed, the power buffer 50 is disabled (entered into a high impedance mode) by the pause signal SP. Conversely, the resistance measurement circuitry 14 is in high impedance when not measuring: when the pause signal SP has the second value, the input 15 of the readout circuit 14 is in a high impedance state. Advantageously, interference is reduced.

[0082] In an alternative embodiment not shown, the device 10 comprises a temperature sensor connected to the readout circuit 14. Feedback to the control loop is based on measuring the temperature of the heater 11 by using a temperature sensor or one or more temperature sensors in the vicinity of the heater 11. This results in the need for additional bond pads and additionally also causes additional thermal power consumption in the heater 11.

[0083] Figure 2A An example of a module 40 is shown, which is Figure 1A and 1B Another improvement of the module shown in FIG. Module 40 is manufactured as a gas sensor module. Figure 2A, a cross section of a module 40 is shown. The module 40 includes a heating plate structure 60 that can be manufactured as a micro-heating plate structure. The module 40 includes a substrate 61 and a membrane 62 supported on the substrate 61. The substrate 61 can be a silicon body or a silicon-on-insulator body. The membrane 62 can be implemented as a dielectric membrane. The membrane 62 includes a heater 11. The heater 11 can have a zigzag or zigzag shape, or have a ring or spiral shape. The zigzag, zigzag, ring or spiral shape of the heater 11 can be seen from an angle on one side of the module 40, such as from a top or bottom view. The heater 11 can be circular or rectangular. The material of the heater 11 can include materials such as aluminum, copper, titanium, molybdenum, tungsten, titanium nitride, nickel, platinum, gold, polycrystalline silicon or single crystal silicon. The heater 11 can be implemented as a CMOS interconnect metal, and the membrane 62 can be implemented by using a CMOS dielectric layer. Therefore, the module 40 can be manufactured by complementary metal oxide semiconductor technology (referred to as CMOS technology).

[0084] The module 40 includes a cavity 63. The membrane 62 spans the cavity 63. The heater 11 is positioned adjacent to the cavity 63. The cavity 63 in the substrate 61 can be formed by etching the substrate 61 in its entirety using an etching technique. The etching technique can be deep reactive ion etching (DRIE) or anisotropic or crystal wet etching, for example, by using an etchant such as potassium hydroxide (KOH) or tetramethylammonium hydroxide (TMAH). Thus, the module 40 is manufactured as a MEMS device.

[0085] The membrane 62 includes a first dielectric layer 66 and a second dielectric layer 67. The first dielectric layer 66 is arranged on the substrate 61. The second dielectric layer 67 is arranged on the first dielectric layer 66. The heater 11 is positioned between the first dielectric layer 66 and the second dielectric layer 67. The membrane 62 may include a passivation layer 68 arranged on the second dielectric layer 67. The heater 11 may be connected to the first terminal 12 and the second terminal 13 via connecting lines 64, 65. The connecting lines 64, 65 may be referred to as heater traces or metallization lines. The first terminal 12 and the second terminal 13 of the heater 11 may be connected to bonding pads of the integrated circuit 58 by wire bonding, for example, as Figure 5A and 5B As shown. The first terminal 12 and the second terminal 13 can be implemented as bonding pads or bonding areas (not shown). Openings (not shown) in the passivation layer 68 and in the second dielectric layer 67 can allow the connection lines 64, 65 to be contacted to the two bonding pads. The first and second dielectric layers and the passivation layers 66 to 68 can contain silicon dioxide, silicon nitride, silicon carbide, tantalum pentoxide or other dielectric layers or combinations of dielectric layers.

[0086] Module 40 includes a sensing material 69 arranged on membrane 62, for example, on passivation layer 68. Sensing material 69 may also be referred to as a sensitive material or a gas-sensitive material. Sensing material 69 interacts with the gas to be measured by module 40. Module 40 includes sensing electrodes 70, 71. Sensing electrodes 70, 71 may be implemented as interdigitated electrodes. Sensing electrodes 70, 71 may be platinum or gold. Sensing electrodes 70, 71 may include an additional adhesion layer or diffusion barrier layer. Therefore, sensing electrodes 70, 71 form interdigitated capacitors. Sensing material 69 is arranged on sensing electrodes 70, 71. Sensing material 69 covers sensing electrodes 70, 71. Sensing electrodes 70, 71 are implemented to measure impedance values ​​(such as resistance values ​​or dielectric constants of sensing material 69). Sensing material 69 may include a metal oxide material selected from a group including: tin oxide, tungsten oxide, zinc oxide, chromium oxide, chromium titanium oxide, gallium oxide, indium oxide, molybdenum oxide, or a combination of the metal oxides. The metal oxide may be mixed with other catalysts or dopants such as platinum or palladium. The sensing material 69 can also be a polymer, or a nanomaterial such as silicon nanowires, carbon nanotubes, graphene, or a metal oxide nanowire such as zinc oxide nanowire. The resistance value of such a metal oxide will vary depending on the gas such as a reducing gas (e.g., CO, H2, H2S, C x H y and C x H y OH) or oxidizing gases (such as O2 and NO x ))'s concentration to change its value.

[0087] The sensing electrodes 70, 71 are connected to the first terminal and the second terminal of the sensor element 41 by connecting lines not shown. The sensor evaluation circuit 56 is configured to measure the resistance value of the sensing material 69 by using the sensing electrodes 70, 71. Therefore, the module 40 is implemented as a resistive gas sensor or a chemical resistor. The module 40 is implemented as a metal oxide gas sensor, which can also be called a metal oxide semiconductor gas sensor.

[0088] The sensing material 69 can be heated to a high temperature, for example 200 to 500°C. This high temperature increases the sensitivity to the target gas, increases the response time (higher temperature means faster reaction time), and also reduces the material resistance (which can be in the order of GΩ at room temperature and is therefore difficult to measure). The temperature setting can be affected by various factors, such as ambient temperature changes, air flow over the sensor surface, or equipment changes (such as the size and thickness of the membrane). Since the temperature affects the resistance of the sensing material, it is important to keep the temperature constant. Otherwise, it is not known whether the change in resistance is due to temperature changes or due to changes in the concentration of the gas. In addition, if the temperature change is too large, the sensitivity will be affected, and the sensor may no longer be sensitive to the target gas.

[0089] Advantageously, the circuit comprising the modulator 19 , the heater 11 , the readout circuit 14 and the digital controller 16 allows for precise regulation of the temperature of the heater 11 and of the sensor element 41 .

[0090] The device 10 implements a gas sensing device that employs one or more heated sensors. In order to be sensitive to the gas, they must be heated to a high temperature (200-500° C.) by using a so-called heating plate 60 that is separate from the integrated circuit 58. The integrated circuit 58 can be manufactured as an application-specific integrated circuit (ASIC for short). The overall structure of the device 10 is shown in FIG. Figure 1A , 1B , 5A and 5B, and the structure of the heating plate 60 is shown in Figure 2A Shown in.

[0091] In an alternative embodiment not shown, the module 40 is implemented as a calorimetric gas sensor. Such a calorimetric gas sensor can also be called a catalytic gas sensor or a varistor. In this case, the sensing electrodes 70, 71 are omitted. The heater 11 raises the temperature of the sensing material 69. Therefore, the gas that must be detected burns at the sensing material 69. The sensing material 69 can be a catalytic material or catalyst (such as palladium or platinum). The catalytic material can be fixed in or on a carrier (such as an alumina ceramic). The sensing material 69 has the function of increasing the combustion rate of the gas at the hot surface of the heating plate structure 60. The calorimetric gas sensor is sensitive to combustible gases, for example.

[0092] In this case, the sensing material 69 catalyzes the combustion of the target gas (if present), which increases the temperature of the membrane 62. The temperature of the heater 11 depends on the electric power supplied to the heater 11 and on the electric power generated by the combustion gas at the sensing material 69. In the constant temperature mode, the temperature of the heater 11 is kept constant by adjusting the electric power supplied to the heater 11. The electric power decreases as the concentration of the combustible gas increases. The electric power supplied to the heater 11 has a maximum value when the concentration of the combustible gas is zero. The sensor evaluation circuit 56 can measure the electric power supplied to the heater 11, for example, by counting pulses of the modulator output signal SM or the circuit signal SCI during a predetermined measurement time. The sensor evaluation circuit 56 can be connected to the output 22 of the modulator 19.

[0093] Alternatively, the sensor signal SE is equal to or proportional to the control signal SC. The power supplied to the heater 11 is proportional to the sigma-delta control signal SC and the supply voltage of the output buffer 50.

[0094] In an alternative embodiment not shown, module 40 includes another sensor element. The other sensor element may include a sensing material different from the sensing material 69 of sensor element 41. Thus, device 10 implements an array of gas sensors. Heater 11 or another heater can heat the other sensor element. For example, the other sensor element can be sensitive to humidity, and sensor element 41 can be sensitive to another gas. This can, for example, allow correction of humidity cross-sensitivity of sensor element 41.

[0095] Alternatively, both the other sensor element and the sensor element 41 may be sensitive to gases - each sensitive to different gases. As another example, both sensor elements 41 may be sensitive to a range of gases, but with different sensitivities to each gas. Furthermore, the sensor array may include any number of sensors, and is not limited to two. The gas sensor array may be all on a single chip (e.g., Figure 5B The array may be entirely on a single membrane with a common heater or separate heaters. Alternatively, the array may have gas sensor elements 41 (such as Figure 5B ). The array may also include separate types of sensors, such as resistive gas sensors, calorimetric gas sensors, and thermal conductivity gas sensors, and / or any combination of these, with zero, one, or more sensors of each type.

[0096] Figure 2B An example of a module 40 is shown, which is Figure 1A , 1B2A. Module 40 does not have sensor element 41. Module 40 does not have sensing material 69 and sensing electrodes 70, 71. Therefore, device 10 is implemented as an infrared transmitter. Module 40 operates as an IR transmitter.

[0097] The module 40 may additionally have one or more layers to improve the emissivity and / or spectral distribution of the heater 11. The additional one or more layers can be on or below the membrane 62. The additional one or more layers may include or consist of a high emissivity material, such as a black metal (e.g., black gold or black platinum), a porous metal, a high emissivity polymer, black carbon, carbon nanotubes, or graphene, or a combination of these. Alternatively, the additional one or more layers may include or consist of a plasma layer above or below the membrane 62 or embedded in the membrane 62. The plasma layer includes a metal or dielectric material patterned into a periodic pattern (such as a periodic hexagonal pattern of dots or holes).

[0098] Advantageously, the stability of the heater 11 is increased by encapsulating between the first dielectric layer 66 and the second dielectric layer 67. The IR emitter can also be array-type. Therefore, the module 40 includes more than one heater 11. The more than one heater 11 is arranged in an array.

[0099] Alternatively, the device 10 (such as Figure 2B Module 40 is implemented as a thermal conductivity sensor. Module 40 operates as a thermal conductivity sensor. The electrical energy supplied to heater 11 is partially converted into IR radiation (as described above) and partially converted into heat. The heat partially flows through membrane 62 to substrate 61, and partially flows through the gas below and above membrane 62. Therefore, the heat conducted out of heater 11 depends on the thermal conductivity of the gas above and below membrane 62. In the case where the temperature of heater 11 is kept constant by device 10, the thermal conductivity of the gas above and below membrane 62 can be measured by measuring the power supplied to heater 11. The power is equal to, for example, control signal SC or is proportional to, for example, control signal SC. At a constant temperature of heater 11, IR emission and heat conduction through membrane 62 are constant. Therefore, a change in the thermal conductivity of the gas above and below membrane 62 causes a change in control signal SC and the thermal conductivity change can be determined. Thermal conductivity is a measure of gas concentration, for example, in a binary gas mixture.

[0100] Figure 2C An example of a module 40 is shown, which is Figure 2BAnother improvement of the module shown. The module 40 operates as a thermal conductivity sensor. The module 40 includes a heat sink 72. A top cavity 73 is between the heat sink 72 and the membrane 62. The heat sink 72 includes at least one opening 74 to allow gas exchange between the top cavity 73 and the external area of ​​the module 40. The measurement of the thermal conductivity of the gas in the top cavity 73 can be performed as described above. The heat sink 72 can be implemented by a material with high thermal conductivity (such as silicon or metal). Therefore, the heat sink 72 has approximately the same temperature as the substrate 61. Advantageously, the effect of gas movement on the measurement is reduced.

[0101] Optionally, the module 40 includes a temperature sensor 75 that measures the temperature of the substrate 61. Therefore, the temperature sensor 75 measures the temperature of the heat sink 72. The thermal conductivity of the gas in the top cavity 73 can be calculated based on the power value provided to the heater 11, the temperature value of the heater 11 (which can be predetermined), and the measured value of the temperature of the temperature sensor 75.

[0102] Figure 3A An example of a temperature characteristic of a device 10 which can be implemented as one of the devices shown above is shown. The heater 11 can have a Figure 3A The temperature distribution shown. The temperature of the heater 11 starts from a first value (e.g., room temperature) and rises to a second value (e.g., 400° C.) and remains constant during a measurement time, such as 40 milliseconds. Afterwards, the temperature drops to the first value. Therefore, the heater 11 is driven in a pulse mode. The measurement of the gas sensor is performed during the measurement time. Since the heating is performed only during a short period of time, the average electrical power used to heat the module 40 is reduced.

[0103] The device 10 solves the problem of keeping the temperature of a heated sensor constant through closed loop control while minimizing thermal transients and power consumption. The heater 11 can be driven in a continuous mode (always on) or in a pulsed mode (where it is only on for a short time, typically 20ms to 10s, and then off for a longer time). Pulsed mode is particularly useful in portable applications because it reduces the power consumption of the device 10. Having a fast transient time allows for a shortened on time during pulsed mode, which allows for lower power consumption (by having a lower duty cycle) or higher frequency pulses (meaning a higher measurement frequency). Figure 3A An example of temperature distribution in the heating plate 60 is shown in FIG.

[0104] Figure 3B An example of the characteristics of a modulator 19 which may be implemented as the device 10 shown in one of the above-shown Figures is shown. Figure 3B In FIG. 5 , the spectrum of the modulator output signal SM is shown. The amplitude MA of the modulator output signal SM is shown as depending on the frequency f. According to Figure 3B In the example in FIG. 1 , the amplitude MA is less than -40 dB for almost every frequency value. The amplitude MA is particularly low in a frequency range including audible frequencies (such as up to 10 kHz). Advantageously, the sigma-delta modulator 19 does not have a defined period, and the power level is related to the pulse density. The emission spectrum is continuous, such as Figure 3B Another advantage is that even with a low system clock the resolution is much higher.

[0105] The device 10 includes a specific closed loop architecture that keeps the temperature on the heater 11 constant by using a digital control loop and a sigma-delta driver 19. This power efficient solution allows very high resolution even at moderate clock frequencies and allows to avoid concentrating the electrical emission in a specific frequency. In addition, sigma-delta reduces temperature ripple compared to PWM modulation generated in the digital domain. The heater 11 itself is used as a thermal sensor. The temperature is measured by turning off the driver 50 for a short time (much shorter than the hot time of the heater 11) and then measuring the resistance of the heater 11. The driver 50 is then turned on and the control loop accounts for the time when the heater bias is turned off. The temperature is then calculated based on the heater resistance.

[0106] Figure 4A 1 shows a typical signal of a heater power supply using pulse width modulation. The current I flowing through the heater 11 repeats after a period T. The period T has a predetermined constant value. During the on-time Ton within the period T, the current I has a first value I1. During the off-time Toff within the period T, the current I has a value of 0A. In order to increase the average current supplied to the heater 11, the on-time Ton is increased by, for example, a time difference ΔT. Figure 1A and 1B In the case where the modulator 19 shown is implemented as a pulse width modulator instead of a sigma-delta modulator, a current I may be provided to the heater 11 .

[0107] Figure 4B An example of a spectrum of a modulator signal SM implemented as a pulse width modulated signal is shown. Figure 4A As shown, the current I in the form of a pulse width modulated signal results in a high amplitude MA even at low frequency values. Therefore, high values ​​in the spectrum may cause audible interference in other parts of the apparatus including the device 10.

[0108] Two strategies for generating pulses can be used: PWM or sigma-delta. PWM uses a periodic waveform such as Figure 4AThe main disadvantage is that the emission spectrum is concentrated at multiples of the PWM frequency; for example, if 10kHz is used, it will affect audio equipment (such as the microphone in a phone). The spectrum of the PWM signal is shown in Figure 4B As shown. The PWM waveform also causes a temperature ripple of the heating plate 60, which can cause noise in the measurement of the resistance of the sensing material; to mitigate this effect, a very high frequency is used. In addition, the resolution of the digital implementation is related to the minimum change in the turn-on phase, which drives the requirement for the system clock; in order to achieve good resolution, a high clock is required, but this also means a higher emission level.

[0109] Figure 5A An example of a device 10 of another improvement of the example shown in the above figures is shown. The device 10 comprises a carrier 80. The module 40 is arranged on the carrier 80. For example, the device 10 comprises glue 81 for fixing the module 40 to the carrier 80. Figure 5A As shown, the glue 81 can be implemented by using four points 81, 81', 81", 81'". The four points 81, 81', 81", 81' of glue are arranged at the four corners of the module 40. Figure 5A As shown, in top view, the cavity 63 has a circular form. A plurality of bonding wires 83 connect the module 40 to the carrier 80 or to the integrated circuit 58 , for example to conductive lines 84 , 84 ′, 84 ″ on the carrier 80 .

[0110] In addition, the device 10 includes an integrated circuit 58. The integrated circuit 58 and the module 40 are implemented as separate semiconductor bodies. The integrated circuit 58 is attached to the carrier 80 by another glue 82. The other glue is shown at all four sides of the integrated circuit 58. The integrated circuit 58 is also connected to the carrier 80 by bonding wires 85, for example, to the conductive lines on the carrier 80. The carrier 80 can be implemented as a printed circuit board (PCB for short), a ceramic carrier (such as a thin film or thick film ceramic substrate) or a socket (such as a TO socket). The housing, not shown, can encapsulate the carrier 80 together with the integrated circuit 58 and the module 40. The housing has an opening to allow the gas to be measured to contact the sensing material 69.

[0111] like Figure 5A As shown, the physical connection between the integrated circuit 58 and the heater 11 (and all other components on the off-chip module 40) is made via direct bonding wires or bonding wires to the package substrate 80. The heater 11 can increase the temperature of the substrate 61 of the module 40. By using two semiconductor bodies, the impact of the module 40 on the integrated circuit 58 is advantageously reduced. The module 40 and the integrated circuit 58 can be produced using different manufacturing technologies.

[0112] In an alternative embodiment not shown, the integrated circuit 58 and the module 40 are implemented on a single semiconductor body.

[0113] Figure 5B An example of a device 10 is shown which is a further development of the examples shown in the above figures. Figure 5B The upper part shows a top view, and Figure 5B The lower part of shows a cross section of the device 10. The module 40 is attached to the integrated circuit 58, for example by means of glue 81, 81'. The module 40 is positioned on the integrated circuit 58. The integrated circuit 58 is between the module 40 and the carrier 80. Therefore, the module 40 is not directly fixed on the carrier 80. The carrier 80 can be implemented as a packaging substrate. The bonding pad 86 of the module 40 is connected to the connecting line 64 of the module 40. At least one bonding wire 83, 83', 83", 83'" connects the bonding pad 86 of the module 40 to the bonding pad 86' of the integrated circuit 58. The integrated circuit 58 can be manufactured as an application-specific integrated circuit (abbreviated as ASIC).

[0114] The module 40 is implemented as a gas sensor array. Therefore, the module 40 includes an array of sensor elements 41, 41', 41", 41'". The number of sensor elements 41, 41', 41", 41'" can be, for example, two, three, four or more than four. The sensor elements 41, 41', 41", 41'" can be positioned in a regular manner. For example, the number is four, and the four sensor elements 41, 41', 41", 41'" are positioned on the four edges of a rectangle or a square. The sensor elements 41, 41', 41", 41'" can include different sensing materials 69 and / or be heated to different temperatures. Each of the sensor elements 41, 41', 41", 41'" includes a heating plate structure 60 having a membrane 62, 62', 62", 62'".

[0115] Advantageously, the gas sensor chip 40 can be placed on top of the ASIC wafer 58, glued together by wafer attach 81, 81'. There are bonding pads 86, 86' on the gas sensor chip 40 and the ASIC chip 58, which can be connected by wire bonding 83.

[0116] Figure 5C An example of a device 10 is shown which is a further development of the device shown above. The device 10 is implemented as a gas sensor which is implemented as an optical gas sensor. The device 10 is configured as an IR sensor, in particular as a non-dispersive infrared sensor (NDIR sensor for short). The module 40 operates as an IR emitter. The heater 11 is implemented as an IR radiation emitter.

[0117] The device 10 includes a module 40 operating as an IR emitter, a detector 76, an optical filter 77, and an optical path 78. A perforated path 79 provides a sample to be analyzed to the optical path 78. The device 10 also includes electrical connections 88, 88' to the module 40 and to the detector 76. The detector 76 is implemented as an optical detector (such as an IR detector). The chamber 87 of the device 10 can contain a gas sample inside the optical path 78. The chamber 87 can be implemented as a tube.

[0118] The perforated path or path opening 79 allows ambient air in the environment to diffuse into the chamber 87 and into the optical path 78. The heater 11 emits IR radiation which passes through the optical filter 77 and reaches the detector 76. The optical filter 77 is such that it allows only a narrow band of wavelengths of the IR radiation to reach the detector 76. The narrow band at least partially overlaps with the absorption wavelength of the target gas.

[0119] As the concentration of the target gas increases, more IR radiation within the band of optical filter 77 is absorbed by the gas and less IR radiation reaches detector 76, giving a lower output signal at detector 76. Changes in the signal from detector 76 can be used to determine the concentration of the target gas.

[0120] The module 40 is configured as an IR emitter. Therefore, the heater 11 is designed as an IR radiation emitter. The IR emission is performed by a MEMS-based IR emitter based on a micro-heating plate. Alternative embodiments of the IR emitter can be a micro bulb or an infrared emitting diode. In the case of a MEMS-based or diode-based IR emitter, it can be directly attached to the PCB or packaged in a TO can package or SMD package. A window or filter can also be integrated into the package.

[0121] The detector 76 for detecting IR radiation can be a thermopile, a pyroelectric, a bolometer or a photodiode. The detector can be packaged as a TO package or SMD, and may or may not have an optical filter 77 integrated into the package. The optical path 78 is shown here as a tube, but it is obvious that many variations are possible, such as by using reflections of the IR emission from the walls 87 of the chamber, and can be a circular path, or a single reflection, or relying on multiple reflections.

[0122] The inlet 79 for ambient air can be connected to the optical path 78 in any number of ways. Figure 5C The is shown in having multiple holes in the tube, but could be a single large or small inlet and could have a particle filter for protection.

[0123] Figure 5DAn example of a device 10 of another development of what is described above is shown. The device 10 is implemented as a gas sensor implemented as an optical gas sensor. The device 10 is configured as a photoacoustic sensor. The module 40 operates as an IR emitter. The heater 11 is implemented as an IR radiation emitter.

[0124] The device 10 implementing the photoacoustic sensor includes a module 40 for implementing an IR emitter, a detector 76 implemented as a microphone, an optical filter 77, and an optical path 78. The device 10 may include a perforated path 79 to the optical path 78. The optical path 78 may be positioned in a cavity 87 of the device 10. In addition, electrical connections 88, 88' are connected to the module 40 and the detector 76. The microphone 76 does not have to be in the visible line of the IR emitter 11.

[0125] The perforated path 79 or path opening allows ambient air in the environment to diffuse into the optical path 78 or chamber 87. The module 40 emits infrared radiation, which passes through the optical filter 77 and heats the air around the detector 76 implemented as a microphone. This causes the air to expand and change the pressure detected by the microphone 76. The optical filter 77 is implemented so that it only allows a narrow band of wavelengths of IR radiation to reach the microphone package. The narrow band overlaps at least partially with the absorption wavelength of the target gas. When the concentration of the target gas increases, more IR radiation in the band of the optical filter 77 is absorbed by the gas in the optical path 78, and the IR radiation reaching the detector 76 (i.e., the microphone package) is reduced, resulting in a lower pressure change, thereby giving a lower output signal at the microphone. The signal change of the detector 76 implemented by the microphone can be used to determine the concentration of the target gas. The module 40 implementing the IR transmitter can be operated in a pulsed mode. The module 40 is manufactured as a MEMS-based IR transmitter implemented by a micro-heating plate.

[0126] Alternatively, the IR emitter can be a micro bulb or an IR emitting diode. In the case of a MEMS-based or diode-based IR emitter, it can be directly attached to the PCB or packaged in a TO can package or SMD package. A window or filter can also be integrated into the package.

[0127] The microphone 76 may be packaged together with the optical filter 77, and the package may or may not be completely airtight. The optical path 78 is shown here as a tube, but it will be apparent that many variations are possible, such as by using reflections of the IR emissions from the walls of the chamber 87 or the optical path 78, and can be a circular path, or a single reflection, or relying on multiple reflections. The inlet 79 for ambient air may be connected to the optical path 78 in any number of ways. Such as Figure 5DIt is shown with multiple holes in the tube, but could be a single large or small inlet, and could have a particle filter for protection. This is given as an example, but many variations of photoacoustic sensors are possible.

[0128] Fig. 6A An example of an apparatus 90 is shown, which has an electrothermal based device 10 implemented as above. The apparatus 90 is implemented as a mobile device 91. The device 10 is incorporated inside the mobile device 91. The cover of the mobile device 91 has an opening 92 for air to enter the device 10. The mobile device 91 may be a device for mobile communication, a smart device, a smart speaker, or a home automation device.

[0129] Figure 6B An example of an apparatus 90 is shown, which has an electrothermal-based device 10 implemented as above. The apparatus 90 is implemented as an indoor air monitor. The apparatus 90 has a housing 93 that houses the apparatus 10. The housing 93 includes a screen 94 to allow the gas to be detected to penetrate the apparatus 10. The apparatus 90 may include, for example, a battery 95 connected to the apparatus 10 for power supply. An indicator 96 may be connected to the apparatus 10. When the apparatus 10 measures that the gas concentration exceeds a predetermined threshold, the indicator 96 is implemented as, for example, a buzzer and / or a light source that provides an alarm. The apparatus 90 may be fixed to a top plate 97.

[0130] Alternatively, the device 90 is implemented as an outdoor air monitor, a car air monitor, and an industrial air or gas monitor.The device 90 may be portable or fixed to a carrier (such as a ceiling 97, a wall, a machine, etc.).

[0131] Alternatively, the apparatus 90 may be connected to a mobile device (such as a device for mobile communication, a smart device, a smart speaker, or a home automation device) by cable or wirelessly. The apparatus 90 may provide the measurement results to the mobile device and / or receive electrical power from the mobile device.

[0132] The electrothermal based device 10 can also be referred to as an electrothermal device, a MEMS device, or a device.

[0133] Description of Reference Numerals

[0134] 10. Equipment

[0135] 11. Heater

[0136] 12 First terminal

[0137] 13 Second terminal

[0138] 14 Readout Circuit

[0139] 15 Input

[0140] 16 Digital Controller

[0141] 17 First Input

[0142] 18 First output

[0143] 19 Digital sigma-delta modulator

[0144] 20 First input

[0145] 21 Output

[0146] 22 Output

[0147] 23 System clock

[0148] 24, 25 Clock input

[0149] 26 Second output

[0150] 27 Second input

[0151] 28 Second input

[0152] 30 Analog-to-digital converter

[0153] 31 Sample and hold circuit

[0154] 32 Analog front end circuit

[0155] 33 Current Source

[0156] 34 Amplifier

[0157] 40 modules

[0158] 41, 41', 41", 41"' sensor element

[0159] 50 Power Buffer

[0160] 51 Σ-Δ Modulator Circuit

[0161] 53 Control Input

[0162] 55 Logic Circuit

[0163] 56 Sensor Evaluation Circuit

[0164] 57 Control Circuit

[0165] 58 Integrated Circuits

[0166] 59 Reference potential terminal

[0167] 60 Heating plate structure

[0168] 61 Substrate

[0169] 62, 62', 62", 62"' membrane

[0170] 63 Cavity

[0171] 64, 65 connection lines

[0172] 66, 67 Dielectric layer

[0173] 68 Passivation layer

[0174] 69 Sensing Materials

[0175] 70, 71 Sensing electrodes

[0176] 72 Radiator

[0177] 73 Top cavity

[0178] 74 Opening

[0179] 75 Temperature Sensor

[0180] 76 Detector

[0181] 77 Optical Filters

[0182] 78 Optical Path

[0183] 79 Perforation Path

[0184] 80 Carrier

[0185] 81, 82 glue

[0186] 83, 83', 83", 83"' bonding wire

[0187] 84, 84', 84" Conducting Line

[0188] 85, 85', 85", 85"' bonding wire

[0189] 86, 86' Bonding pad

[0190] 87 Chamber

[0191] 88, 88' electrical connection

[0192] 90 Devices

[0193] 91 Mobile devices

[0194] 92 Opening

[0195] 93 Shell

[0196] 94 Screen

[0197] 95 Batteries

[0198] 96 Indicator

[0199] 97 Top Plate

[0200] f Frequency

[0201] I, I1 current

[0202] SC control signal

[0203] SCI circuit signal

[0204] SE sensor signal

[0205] SM modulator output signal

[0206] SO1, SO2 clock signal

[0207] SP Pause signal

[0208] SR readout signal

[0209] ST Target Signal

[0210] t time

[0211] T Temperature.

Claims

1. An electric heating device comprising: - Heater (11), - readout circuit (14), - a digital controller (16), a first input (17) of the digital controller being coupled to a first output (18) of the readout circuit (14), and - a digital sigma-delta modulator (19), a first input (20) of the digital sigma-delta modulator being coupled to an output (21) of the digital controller (16) and an output (22) of the digital sigma-delta modulator being connected to a first terminal (12) of the heater (11), in, The readout circuit (14) has a first terminal (12) connected to the heater (11) so that the heater (11) is electrically coupled to an input (15) of the readout circuit (14), The digital sigma-delta modulator (19) is configured to generate a modulator output signal, wherein the digital sigma-delta modulator (19) comprises a second input (27) for receiving a pause signal, and the digital sigma-delta modulator is configured to generate a modulator output signal having a constant value of zero when the pause signal has a first value, and to generate a modulator output signal whose value depends on a control signal provided to the digital sigma-delta modulator when the pause signal has a second value, wherein the readout circuit (14) comprises a second output (26) coupled to a second input (27) of the digital sigma-delta modulator (19), and The readout circuit (14) is configured to generate the pause signal and to determine the readout signal when the pause signal has a first value.

2. The electrothermal based device of claim 1, which is a gas sensor or a gas sensor array.

3. The electrothermal based device of claim 1, which is an infrared emitter.

4. The electrothermal based device of claim 1, which is a thermal conductivity sensor.

5. The electrothermal based device according to any one of claims 1 to 4, said device being a micro-electromechanical system device having a membrane (62), wherein: The heater (11) is embedded.

6. An electrothermal based device according to any one of claims 1 to 4, in, The readout circuit (14) is configured to generate the readout signal at a first output (18) of the readout circuit (14), and The digital controller (16) comprises a second input (28) for receiving a target signal, and is configured to generate the control signal based on the read signal and the target signal, and to provide the control signal to the first input (20) of the digital sigma-delta modulator (19).

7. The electrothermal based device of claim 1, wherein: The digital sigma-delta modulator (19) comprises a sigma-delta modulator circuit (51) and a power buffer (50), and Wherein, the power buffer (50) comprises - an input connected to the output of the sigma-delta modulator circuit (51), - an output connected to the output (22) of the digital sigma-delta modulator (19), and - a control input (53) connected to a second input (27) of the digital sigma-delta modulator (19).

8. An electrothermal based device according to any one of claims 1 to 4, in, The readout circuit (14) is configured to generate a readout signal according to a resistance value of the heater (11).

9. An electrothermal based device according to any one of claims 1 to 4, in, The digital controller (16) is implemented as a proportional-integral-derivative PID digital controller or a proportional-integral PI digital controller.

10. A device (90), The device comprises an electrothermal-based apparatus (10) according to one of claims 1 to 4, in, The device (90) is implemented as one of the following: a mobile device (91), an indoor air monitor, an outdoor air monitor, a car air monitor, and an industrial gas monitor.

11. A method for operating a heater (11) in an electrothermal based device (10), the method comprising - supplying the modulator output signal to a heater (11), - generating a readout signal by a readout circuit (14), and - generating a control signal by a digital controller (16) based on the read signal, wherein a digital sigma-delta modulator (19) generates the modulator output signal, in, The output (22) of the digital sigma-delta modulator (19) is connected to the first terminal (12) of the heater (11), wherein an input (15) of the readout circuit (14) is connected to a first terminal (12) of the heater (11) so that the heater (11) is electrically coupled to the readout circuit (14), wherein the digital sigma-delta modulator (19) comprises a second input (27) for receiving a pause signal, and the digital sigma-delta modulator generates a modulator output signal having a constant value of zero when the pause signal has a first value, and generates a modulator output signal whose value depends on the control signal when the pause signal has a second value, wherein the readout circuit (14) comprises a second output (26) coupled to a second input (27) of the digital sigma-delta modulator (19), and The readout circuit (14) generates the pause signal and determines the readout signal when the pause signal has a first value.

12. The method according to claim 11, wherein: A readout signal is generated according to the resistance value of the heater (11).

13. The method according to claim 11 or 12, in, The modulator output signal is implemented as a pulse signal, and Therein, the readout signal and the control signal are implemented as digital signals.

Images