A heat exchange accelerometer and heating control method thereof

Abstract

The present invention discloses a heat exchange accelerometer and a heating control method thereof. The heating control method comprises: sensing the temperature in a closed cavity and generating a temperature voltage signal; amplifying the temperature voltage signal to obtain an amplified temperature voltage signal; obtaining the difference between the amplified temperature voltage signal and the reference voltage signal to obtain a voltage difference signal; converting the voltage difference signal into a digital sequence; summing each N bits in the digital sequence into a group, and then multiplying by a predetermined gain to obtain a heating power adjustment factor; obtaining a heating power control parameter based on the heating power adjustment factor and the heating power initial factor; converting the heating power control parameter into a control switch control signal; using the switch control signal to control the conduction or disconnection of the heating control switch, thereby controlling the heating resistor to heat the closed cavity. In this way, the stabilization speed of the closed-loop control loop can be significantly improved, while avoiding a significant increase in chip area and power consumption.

Description

[Technical field]

[0001] The invention relates to the field of heat exchange type accelerometers, and in particular to a heat exchange type accelerometer with a fast and stable closed-loop heating control circuit and a heating control method thereof. [Background technology]

[0002] Heat exchange accelerometers are based on heating the gas in a closed cavity and detecting the temperature of thermocouples at different positions. In order to obtain stable sensitivity, the temperature of the gas in the closed cavity must be precisely controlled. The existing solution is to use an integrator in the loop of the heating control circuit to make the bandwidth of the loop of the heating control circuit smaller than any pole brought by the accelerometer. The disadvantage is that the temperature stabilization speed is slow, resulting in a lot of time and power consumption to stabilize the temperature of the closed cavity before the accelerometer starts measuring in the on-demand mode, resulting in too low data rate.

[0003] Therefore, it is necessary to provide a new improvement scheme to overcome the above problems. [Summary of the invention]

[0004] The technical problem to be solved by the present invention is to provide a heat exchange accelerometer and a heating control method thereof, which can significantly improve the stabilization speed of a closed-loop heating control circuit while avoiding a significant increase in chip area and power consumption.

[0005] In order to solve the above problems, according to one aspect of the present invention, a heat exchange accelerometer is provided, which includes a body having a closed cavity and a heating control circuit for controllably heating the closed cavity, wherein the heating control circuit includes: a heating resistor for heating the closed cavity; a heating control switch for controlling the power on and off of the heating resistor; a temperature-controlled thermocouple configured to sense the temperature in the closed cavity and generate a temperature voltage signal; an amplifier coupled to the temperature-controlled thermocouple, configured to amplify the temperature voltage signal to obtain an amplified temperature voltage signal; and a modulator configured to convert the voltage difference signal into a digital signal. sequence, wherein the voltage difference signal is the difference between the amplified temperature voltage signal and a reference voltage signal; a heating power adjustment module coupled to the modulator, configured to obtain a heating power adjustment factor according to the digital sequence, wherein the heating power adjustment factor characterizes the voltage difference signal; a heating power determination module coupled to the heating power adjustment module, configured to obtain a heating power control parameter based on the heating power adjustment factor and the heating power initial factor; a conversion module coupled to the heating power determination module, configured to convert the heating power control parameter into a switch control signal for controlling the conduction or disconnection of the heating control switch.

[0006] According to another aspect of the present invention, the present invention provides a heating control method for a heat exchange accelerometer, the heat exchange accelerometer comprising a body having a closed cavity and a heating control circuit for controllably heating the closed cavity, the method comprising: sensing the temperature in the closed cavity and generating a temperature voltage signal; amplifying the temperature voltage signal to obtain an amplified temperature voltage signal; obtaining a difference between the amplified temperature voltage signal and a reference voltage signal to obtain a voltage difference signal; converting the voltage difference signal into a digital sequence using a modulator; obtaining a heating power adjustment factor based on the digital sequence; obtaining a heating power control parameter based on the heating power adjustment factor and the heating power initial factor; converting the heating power control parameter into a control switch control signal; and controlling the conduction or disconnection of a heating control switch using the switch control signal, thereby controlling a heating resistor to heat the closed cavity.

[0007] Compared with the prior art, the present invention only uses linear amplification in the closed-loop heating control circuit without introducing the poles of the integrator, so a larger bandwidth can be achieved, which can significantly improve the stable speed of the closed-loop heating control circuit while avoiding a significant increase in chip area and power consumption.

[0008] Other objects, features and advantages of the present invention will be described in detail below in conjunction with the accompanying drawings in the specific implementation manner.

Brief Description of the Drawings

[0009] The present invention will be more easily understood with reference to the accompanying drawings and the following detailed description, wherein like reference numerals correspond to like structural components, wherein:

[0010] Figure 1 It is a structural block diagram of a heating control circuit of a heat exchange accelerometer in the present invention in one embodiment;

[0011] Figure 2 is the loop gain of the conventional integrator-based heating control circuit;

[0012] Figure 3 It is the loop gain of the heating control circuit using only linear amplification in the present invention. [Specific implementation method]

[0013] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0014] The term "one embodiment" or "embodiment" as used herein means that a particular feature, structure or characteristic associated with the embodiment may be included in at least one implementation of the present invention. The term "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor does it necessarily refer to a separate or selected embodiment that is mutually exclusive with other embodiments. The terms "multiple" and "several" in the present invention mean two or more. The term "and / or" in the present invention means "and" or "or".

[0015] The present invention provides a heat exchange accelerometer with a fast and stable closed-loop heating control circuit, which can significantly improve the stabilization speed of the closed-loop heating control circuit while avoiding a significant increase in chip area and power consumption.

[0016] The heat exchange accelerometer in the present invention includes a body having a closed cavity, a heating control circuit for controllably heating the closed cavity, and a plurality of detection thermocouples arranged at different positions of the closed cavity, and an acceleration measurement value is obtained based on the temperature voltage signal generated by each detection thermocouple. This article focuses on the improvement of the heating control circuit 100, so how to obtain the acceleration measurement value based on the temperature voltage signal generated by each detection thermocouple is not described in detail.

[0017] Figure 1 The figure is a schematic structural block diagram of a heating control circuit 100 of a heat exchange accelerometer in the present invention in one embodiment. The heating control circuit includes a heating resistor Rh, a heating control switch S1, a temperature-controlled thermocouple Rt, an amplifier 110, a pressure difference module 120, a modulator 130, a heating power adjustment module 140, a heating power determination module 150 and a conversion module 160.

[0018] The heating resistor Rh heats the closed cavity (not shown) when it is powered on, and stops heating the closed cavity when it is powered off. The heating control switch S1 controls the power on and off of the heating resistor. Figure 1 In the embodiment shown, the heating resistor Rh and the heating control switch S1 are connected in series between the power supply terminal VDD and the ground terminal. In another alternative embodiment, the positions of the heating resistor Rh and the heating control switch S1 can be interchanged, that is, the heating control switch S1 and the heating resistor Rh are connected in series between the power supply terminal VDD and the ground terminal. In addition, there can be other connection methods, as long as the heating control switch S1 can control the power on or off of the heating resistor Rh. Specifically, as Figure 1As shown, the on or off of the heating control switch S1 is controlled by the switch control signal Sn. When the switch control signal Sn is at a first logic level, such as a high level, the heating control switch S1 is turned on, and the heating resistor Rh is controlled to be energized to generate heat. When the switch control signal Sn is at a second logic level, such as a low level, the heating control switch S1 is turned off, and the heating resistor Rh is controlled to be de-energized to stop generating heat.

[0019] The temperature-controlled thermocouple Rt is configured to sense the temperature in the closed cavity and generate a temperature voltage signal. The amplifier 110 is coupled to the temperature-controlled thermocouple Rt and is configured to amplify the temperature voltage signal to obtain an amplified temperature voltage signal. The pressure difference module 120 is configured to subtract a reference voltage signal V from the amplified temperature voltage signal. ref A voltage difference signal is obtained. The modulator 130 is configured to convert the voltage difference signal into a digital sequence a[1], a[2], a[i], where i is the i-th digit of the digital sequence. The value of each digit in the digital sequence is one of a first integer value and a second integer value, wherein the sum of the first integer value and the second integer value is 0. For example, the first integer value is 1, the second integer value is -1, and the sum of the two is 0. Depending on the specific needs of the application, the voltage difference module 120 can be implemented together with the amplifier 110, or with the modulator 130, or can be implemented separately. Specifically, the modulator is a Sigma-Delta modulator. When the voltage difference signal is 0, the number of -1 and 1 in the digital sequence output by the Sigma-Delta modulator is the same. As the voltage difference signal is positive or negative, the number of -1 or 1 in the digital sequence output by the Sigma-Delta modulator will increase. The larger the value of the voltage difference signal, the greater the difference between the number of 1 and -1 in the digital sequence.

[0020] The heating power adjustment module 140 is coupled to the modulator 130, and is configured to group a[i], each group containing N consecutive values, namely a[N*(j-1)+1], a[N*(j-1)+2], … a[N*j], and then sum each group in the digital sequence and multiply it by a predetermined gain M to obtain a heating power adjustment factor, where N is a natural number greater than or equal to 2, and j is the number of groups.

[0021] Specifically, the heating power adjustment factor is:

[0022]

[0023] Where M is the predetermined gain, a iis the i-th bit of the digital sequence, b[j] is the j-th heating power adjustment factor corresponding to the j-th digital sequence, and j is an integer greater than or equal to 1. The heating power adjustment factor b[j] can reflect the value of the voltage difference signal, that is, the difference between the instantaneous temperature of the closed cavity and the reference value, and M reflects the correction strength of the loop.

[0024] In another alternative embodiment, the sum of the first integer value and the second integer value may not be 0. For example, the first integer value is 0 and the second integer value is 1. In this case, the sum of the two is 1. In this case, the heating power adjustment module 140 does not group each N bits in the digital sequence into a group and then sum them, and then multiply them by the predetermined gain M to obtain the heating power adjustment factor. Instead, each N bits are grouped into a group and then summed and then subtracted from N / 2, and then multiplied by the predetermined gain M to obtain the heating power adjustment factor. Of course, there can be other alternatives, as long as the heating power adjustment module 140 can obtain the heating power adjustment factor according to the digital sequence, and the heating power adjustment factor can characterize the voltage difference signal. The heating power adjustment factor characterizing the voltage difference signal means that the size of the heating power adjustment factor can reflect the size of the voltage difference signal. When the voltage difference signal tends to 0, the heating power adjustment factor also tends to 0.

[0025] The heating power determination module 150 is coupled to the heating power adjustment module 140, and is configured to obtain a heating power control parameter based on the heating power adjustment factor and the heating power initial factor. Specifically, the heating power control parameter is the sum of the heating power adjustment factor and the heating power initial factor. The heating power control parameter reflects the heating power that the heating resistor Rh provides to the closed cavity.

[0026] Specifically, the heating power control parameter is:

[0027] h[j]=b[j]+c[k] (2)

[0028] h[j] is the j-th heating power control parameter, c[k] is the heating power initial factor, and the heating power initial factor can be a constant.

[0029] The conversion module 160 is coupled to the heating power determination module 150 , and is configured to convert the heating power control parameter into a switch control signal Sn for controlling the on or off of the heating control switch S1 .

[0030] Specifically, the conversion module is a digital integrator, and the expression of its output D[n] is:

[0031] D[n]=D[n-1]+h[n], (3)

[0032] n is the number of iterations, and n is an integer greater than or equal to 1;

[0033] h[n] is the value of the heating power control parameter in this iteration,

[0034] Each time the digital integrator overflows, the switch control signal Sn is at the first logic level and at the second logic level for the rest of the time. After verifying that there are enough clock cycles, the duty cycle of the switch control signal Sn is equal to the ratio of the current value of the heating power control parameter to its full value signal. The equation (3) uses h[n] instead of h[j] because there may be multiple integration operations based on the same h[j] and updates of D[n] in each h[j] update cycle.

[0035] When the closed-loop heating control circuit 100 is stable, the amplified temperature voltage signal is controlled to be stable near the reference voltage signal, which means that the instantaneous temperature of the closed cavity is controlled to be stable near the reference temperature. At this time, the voltage difference signal is stable near 0, the number of -1 and 1 in the digital sequence output by the Sigma-Delta modulator is basically the same, the heating power adjustment factor b[j] approaches 0, the heating power control parameter remains basically unchanged, and the duty cycle of the switch control signal Sn remains basically unchanged. When the closed-loop heating control circuit 100 is unstable, the voltage difference signal is far away from 0, and the heating power adjustment factor b[j] is far away from 0, thereby increasing or decreasing the heating power control parameter, realizing negative feedback control, and then making the amplified temperature voltage signal approach the reference voltage signal, and finally stabilize near the reference voltage signal.

[0036] In the present invention, the expression of b[j] is based on a digital low-pass filter. Due to the high sampling frequency, the cut-off frequency of the low-pass filter is much higher than the cut-off frequency of the accelerometer. Therefore, within the bandwidth of the accelerometer, the low-pass filter can be approximated as a linear amplification of the difference signal. At the same time, the low-pass filter can be implemented with a smaller chip area. Different from the traditional design with an integrator, the system using only linear amplification will not introduce the pole of the integrator, so the lowest frequency pole P0 of the accelerometer can be used as the main pole of the system, and the cut-off frequency f0 of the system is determined by the 0dB point of the loop gain. Figure 2 The loop gain of the system of the present invention (i.e. the closed-loop control system formed by the heating control circuit) is compared with that of the conventional integrator-based system. It can be seen that in the case of the integrator, f0 needs to be significantly smaller than P0 to ensure stability, while in the system using only linear amplification, f0 is greater than P0. Therefore, a larger bandwidth can be achieved.

[0037] from Figure 2It can be found that the loop gain of the system using only linear amplification at DC is significantly smaller than that of the system with an integrator, which means that when c[k] remains unchanged, the error between the final value and the reference value of the temperature of the closed cavity is much greater than that of the system with an integrator. Therefore, preferably, in the present invention, the initial heating power factor can also be updated according to a predetermined rule.

[0038] In one embodiment, the value of c[k] is updated as follows.

[0039] The value of c[k] is stored in a register. When the accelerometer is enabled, the system uses c[k] stored in the register as the initial value c0. When the accelerometer is enabled for the first time after a power-on reset, c[0] is set to 0. Assume h[j] = h target When the output of the amplifier 110 reaches the reference voltage signal V ref , at this time, the probability of 0 and 1 appearing in the data string of a[m] is equal. Due to the existence of errors, after the accelerometer is first enabled, after a long enough time, the final value of h[j] is:

[0040]

[0041] make It can be proven that in the next update cycle

[0042]

[0043] And so on.

[0044]

[0045] Considering that the loop gain G is greater than 1, h i The value is getting closer to h target Assuming the gain G = 3, after 4 iterations, the system error is less than 1%.

[0046] The final value of h[j] obtained in each measurement is stored in a register for the next measurement of c[k]. This way, after a few initial measurement cycles, the accelerometer will accurately reach the target value in a short time.

[0047] According to another aspect of the present invention, the present invention further provides a heating control method for a heat exchange accelerometer, the heating control method comprising:

[0048] sensing the temperature in the closed cavity and generating a temperature voltage signal;

[0049] amplifying the temperature voltage signal to obtain an amplified temperature voltage signal;

[0050] Obtaining a difference between the amplified temperature voltage signal and a reference voltage signal to obtain a voltage difference signal;

[0051] Converting the voltage difference signal into a digital sequence using a modulator;

[0052] Obtaining a heating power adjustment factor based on the digital sequence, wherein the heating power adjustment factor represents the voltage difference signal;

[0053] Obtaining a heating power control parameter based on the heating power adjustment factor and the heating power initial factor;

[0054] Converting the heating power control parameter into a control switch control signal;

[0055] The switch control signal is used to control the conduction or disconnection of the heating control switch, thereby controlling the heating resistor to heat the closed cavity.

[0056] In one embodiment, the value of each digit in the digital sequence is one of a first integer value and a second integer value, wherein the sum of the first integer value and the second integer value is 0, and the heating power adjustment factor is obtained based on the digital sequence as follows: each N bits in the digital sequence are grouped together and summed, and then multiplied by a predetermined gain to obtain the heating power adjustment factor, wherein N is a natural number greater than or equal to 2, and the heating power control parameter is the sum of the heating power adjustment factor and the heating power initial factor.

[0057] In one embodiment, the heating power adjustment factor is:

[0058]

[0059] Where M is the predetermined gain, a i is the i-th digit of the digital sequence, b[j] is the j-th heating power adjustment factor corresponding to the j-th group of digital sequences, and j is an integer greater than or equal to 1.

[0060] The heating power control parameters are:

[0061] h[j]=b[j]+c[k], h[j] is the jth heating power control parameter, and c[k] is the heating power initial factor.

[0062] In one embodiment, the conversion module is a digital integrator, and the expression of its output D[n] is:

[0063] D[n]=D[n-1]+h[n], where n is the number of iterations and n is an integer greater than or equal to 1;

[0064] h[n] is the value of the heating power control parameter in this iteration,

[0065] Each time the digital integrator overflows, the switch control signal is at the first logic level, and at the second logic level the rest of the time.

[0066] The duty cycle of the switch control signal is equal to the ratio of the current value of the heating power control parameter to its full value signal.

[0067] In one embodiment, the final value of the heating power control parameter after a measurement is stored, and the stored heating power control parameter is updated to the heating power initial factor in subsequent measurements, c[k] is the heating power initial factor updated for the kth time, the initial value of the heating power initial factor is equal to 0, and k is an integer greater than or equal to 0.

[0068] In one embodiment, when the switch control signal is at a first logic level, the heating control switch is turned on, and the heating resistor is controlled to be on and off to generate heat. When the switch control signal is at a second logic level, the heating control switch is turned off, and the heating resistor is controlled to be powered off to stop generating heat. The modulator is a Sigma-Delta modulator.

[0069] Compared with the prior art, the present invention only uses linear amplification in the closed-loop heating control circuit without introducing the poles of the integrator, so a larger bandwidth can be achieved, which can significantly improve the stable speed of the closed-loop heating control circuit while avoiding a significant increase in chip area and power consumption.

[0070] In the present invention, words such as “connect”, “connected”, “connect”, “connected”, etc. indicating electrical connection, unless otherwise specified, indicate direct or indirect electrical connection, and “coupled” indicates direct or indirect electrical connection or coupled connection.

[0071] The above description has fully disclosed the specific embodiments of the present invention. It should be pointed out that any changes made by those skilled in the art to the specific embodiments of the present invention do not deviate from the scope of the claims of the present invention. Accordingly, the scope of the claims of the present invention is not limited to the above specific embodiments.

Claims

1. A heat exchange accelerometer, characterized in that: It comprises a body having a closed cavity and a heating control circuit for controllably heating the closed cavity, wherein the heating control circuit comprises: a heating resistor for heating the closed cavity; A heating control switch for controlling the power on and off of the heating resistor; a temperature-controlled thermocouple configured to sense the temperature within the closed cavity and generate a temperature voltage signal; an amplifier coupled to the temperature-controlled thermocouple, configured to amplify the temperature-voltage signal to obtain an amplified temperature-voltage signal; A modulator configured to convert a voltage difference signal into a digital sequence, wherein the voltage difference signal is a difference between the amplified temperature voltage signal and a reference voltage signal; a heating power adjustment module coupled to the modulator, configured to obtain a heating power adjustment factor according to a digital sequence, wherein the heating power adjustment factor represents the voltage difference signal; a heating power determination module coupled to the heating power adjustment module, configured to obtain a heating power control parameter based on the heating power adjustment factor and the heating power initial factor; The conversion module coupled to the heating power determination module is configured to convert the heating power control parameter into a switch control signal for controlling the on or off of the heating control switch.

2. The heat exchange accelerometer according to claim 1, characterized in that: The value of each digit in the digital sequence is one of a first integer value and a second integer value, wherein the sum of the first integer value and the second integer value is 0, and the heating power adjustment module is configured to group each N digits in the digital sequence and sum them, and then multiply them by a predetermined gain to obtain a heating power adjustment factor, wherein N is a natural number greater than or equal to 2, and the heating power control parameter is the sum of the heating power adjustment factor and the heating power initial factor.

3. The heat exchange accelerometer according to claim 2, characterized in that: The heating power adjustment factor is: Where M is the predetermined gain, a i is the i-th digit of the digital sequence, b[j] is the j-th heating power adjustment factor corresponding to the j-th digital sequence, j is an integer greater than or equal to 1, The heating power control parameters are: h[j]=b[j]+c[k], h[j] is the jth heating power control parameter, and c[k] is the heating power initial factor.

4. The heat exchange accelerometer according to claim 3, characterized in that: The conversion module is a digital integrator, and the expression of its output D[n] is: D[n]=D[n-1]+h[n], where n is the number of iterations and n is an integer greater than or equal to 1; h[n] is the value of the heating power control parameter in this iteration, Each time the digital integrator overflows, the switch control signal is at the first logic level, and at the second logic level the rest of the time. The duty cycle of the switch control signal is equal to the ratio of the current value of the heating power control parameter to its full value signal.

5. The heat exchange accelerometer according to claim 3, characterized in that: The final value of the heating power control parameter after a measurement is stored, and the stored heating power control parameter is updated to the heating power initial factor in subsequent measurements, c[k] is the heating power initial factor updated for the kth time, the initial value of the heating power initial factor is equal to 0, and k is an integer greater than or equal to 0.

6. The heat exchange accelerometer according to claim 4, characterized in that: When the switch control signal is at a first logic level, the heating control switch is turned on, and the heating resistor is controlled to be powered on to generate heat. When the switch control signal is at a second logic level, the heating control switch is turned off, and the heating resistor is controlled to be powered off to stop generating heat. The modulator is a Sigma-Delta modulator.

7. The heat exchange accelerometer according to claim 2, characterized in that: It also includes: The detection thermocouples are arranged at different positions of the closed cavity, and the acceleration measurement value is obtained based on the temperature voltage signal generated by each detection thermocouple.

8. A heating control method for a heat exchange accelerometer, the heat exchange accelerometer comprising a body having a closed cavity and a heating control circuit for controllably heating the closed cavity, characterized in that: It includes: sensing the temperature in the closed cavity and generating a temperature voltage signal; amplifying the temperature voltage signal to obtain an amplified temperature voltage signal; Obtaining a difference between the amplified temperature voltage signal and a reference voltage signal to obtain a voltage difference signal; Converting the voltage difference signal into a digital sequence using a modulator; Obtaining a heating power adjustment factor based on the digital sequence, wherein the heating power adjustment factor represents the voltage difference signal; Obtaining a heating power control parameter based on the heating power adjustment factor and the heating power initial factor; Converting the heating power control parameter into a control switch control signal; The switch control signal is used to control the conduction or disconnection of the heating control switch, thereby controlling the heating resistor to heat the closed cavity.

9. The heating control method according to claim 8, characterized in that: The value of each digit in the digital sequence is one of a first integer value and a second integer value, wherein the sum of the first integer value and the second integer value is 0, The heating power adjustment factor is obtained based on the digital sequence as follows: each N bits in the digital sequence are grouped together and summed, and then multiplied by a predetermined gain to obtain the heating power adjustment factor, wherein N is a natural number greater than or equal to 2, The heating power control parameter is the sum of the heating power adjustment factor and the heating power initial factor.

10. The heating control method according to claim 9, characterized in that: The heating power adjustment factor is: Where M is the predetermined gain, a i is the i-th digit of the digital sequence, b[j] is the j-th heating power adjustment factor corresponding to the j-th digital sequence, j is an integer greater than or equal to 1, The heating power control parameters are: h[j]=b[j]+c[k], h[j] is the jth heating power control parameter, and c[k] is the heating power initial factor.

11. The heating control method according to claim 10, characterized in that: The conversion module converts the heating power control parameter into a control switch control signal. The conversion module is a digital integrator, and the expression of its output D[n] is: D[n]=D[n-1]+h[n], where n is the number of iterations and n is an integer greater than or equal to 1; h[n] is the value of the heating power control parameter in this iteration, Each time the digital integrator overflows, the switch control signal is at the first logic level, and at the second logic level the rest of the time. The duty cycle of the switch control signal is equal to the ratio of the current value of the heating power control parameter to its full value signal.

12. The heating control method according to claim 10, characterized in that: The final value of the heating power control parameter after a measurement is stored, and the stored heating power control parameter is updated to the heating power initial factor in subsequent measurements, c[k] is the heating power initial factor updated for the kth time, the initial value of the heating power initial factor is equal to 0, and k is an integer greater than or equal to 0.

13. The heating control method according to claim 10, characterized in that: When the switch control signal is at a first logic level, the heating control switch is turned on, and the heating resistor is controlled to be turned on and off to generate heat. When the switch control signal is at a second logic level, the heating control switch is turned off, and the heating resistor is controlled to be powered off to stop generating heat. The modulator is a Sigma-Delta modulator.

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