MEMS gyroscope driving loop and method
By using charge voltage conversion module, charge pump module and other components in the MEMS gyroscope driving loop, and using differential voltage signals and pulse width modulation signals, efficient driving of the MEMS gyroscope driving capacitor is achieved, solving the problems of high power consumption and high driving noise in the prior art, and improving the anti-interference ability and driving accuracy.
Patent Information
- Application Number
- CN202510267977.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-07
- Publication Date
- 2025-06-24
AI Technical Summary
When the existing MEMS gyroscope drive loop increases the power consumption and drive noise is difficult to control when increasing the charge pump output and oscillation amplitude AC, it is difficult to meet the needs of low power consumption, miniaturization and cost-effectiveness.
A driving loop including a charge voltage conversion module, a charge pump module, a comparator, a phase lock loop module, a driving module, a digital-to-analog converter and a digital module is adopted. Through the combination of differential voltage signals, square wave signals and pulse width modulation signals, efficient driving of the MEMS gyroscope driving capacitor is achieved.
It improves the anti-interference capability of the MEMS gyroscope drive loop, reduces power consumption, and improves driving efficiency and accuracy, making it suitable for consumer electronic applications with low power consumption requirements.
Smart Images
Figure CN120194673A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the technical field of MEMS micromachined system gyroscope chips, and particularly relates to a MEMS gyroscope drive loop and method. Background Art
[0002] A gyroscope is a device used to measure angular rate. Compared with the previous laser gyroscopes, a MEMS gyroscope is a sensor manufactured using microelectromechanical system technology. Its working principle is that first, the drive capacitance of the MEMS gyroscope is operated at the resonant frequency, and then based on the principle of the Coriolis force, when an object rotates, it will be affected by the Coriolis force, causing the micro-mechanical structure inside the MEMS gyroscope to displace. By detecting this displacement, the angular velocity of the object can be measured. With the continuous innovation of miniaturization technology, especially in fields such as industry and consumer electronics, the requirements for low power consumption, miniaturization, and high cost performance of MEMS gyroscopes are getting higher and higher.
[0003] Existing capacitive MEMS gyroscope chips all include a MEMS device and a signal conditioning circuit part. The signal conditioning circuit part includes a drive loop and a detection link. The drive loop causes the MEMS drive capacitance to displace and oscillate at its resonant frequency at all times; the detection link is used to detect the signal generated by the Coriolis force and calculate the angular rate information. The Coriolis force signal is proportional to the displacement and angular velocity of the MEMS drive capacitance. Therefore, in order to keep the sensitivity of the angular velocity sensor unchanged, a drive loop must be designed to make the displacement of the MEMS drive capacitance large enough and remain unchanged. The position of the MEMS drive capacitance is proportional to the driving force hdc*AC, where hdc is the bias voltage of the MEMS mass block and AC is the equivalent amplitude of the AC signal with the same frequency as the MEMS resonant frequency. Due to the increasing requirements for miniaturization, low power consumption, high precision, and cost performance, the supply voltage at the application end is also decreasing.
[0004] In the traditional drive loop using sinusoidal wave drive, due to the drive efficiency problem, not only does the output of the charge pump need to be increased to increase hdc, but often an additional charge pump circuit is also required to increase the oscillation amplitude AC of the sinusoidal wave. The two charge pump circuits not only increase power consumption, but the charge pump for supplying power to the AC signal also requires greater driving ability to drive the MEMS capacitance. And when the AC amplitude increases, the actual equivalent hdc is decreasing. The AC value with a certain driving ability generated by the charge pump is also difficult to control in terms of accuracy, and relatively large driving noise will be introduced. Summary of the Invention
[0005] This application provides a MEMS gyroscope drive loop and method, and its technical objective is to improve the anti-interference ability of the MEMS gyroscope drive loop and reduce power consumption.
[0006] The above technical object of the present application is achieved by the following technical solutions:
[0007] A MEMS gyroscope drive loop. The MEMS gyroscope includes a pair of drive capacitors and a pair of drive detection capacitors. The drive loop includes a charge-voltage conversion module, a charge pump module, a first comparator, a phase-locked loop module, a drive module, a digital-to-analog converter, a digital module, and a band-pass analog-to-digital converter; one end of a pair of drive capacitors is equivalently connected in series with one end of a pair of drive detection capacitors, and the series connection point is biased at a high-voltage bias voltage and connected to the charge pump module; the other end of the pair of drive capacitors is connected to the drive module, and the other end of the pair of drive detection capacitors is connected to the charge-voltage conversion module; the output of the charge-voltage conversion module is input to the first comparator and the band-pass analog-to-digital converter, the output of the first comparator is input to the phase-locked loop module, the output of the phase-locked loop module is input to the digital module, the output of the band-pass analog-to-digital converter is input to the digital module, the output of the digital module is input to the digital-to-analog converter and the drive module, and the output of the digital-to-analog converter is input to the drive module.
[0008] Further, the charge-voltage conversion module is used to detect the change of the drive detection capacitor, convert the change into a differential voltage signal, and then input the differential voltage signal to the first comparator and the band-pass analog-to-digital converter.
[0009] Further, the first comparator converts the differential voltage signal into a square wave signal and inputs the square wave signal as the reference clock of the phase-locked loop module.
[0010] Further, the band-pass analog-to-digital converter quantizes the differential voltage signal and generates a digital signal to be input to the digital module.
[0011] Further, the phase-locked loop module generates a main clock signal according to the square wave signal and inputs the main clock signal to the digital module as the working main clock of the digital module.
[0012] Further, the digital module includes an amplitude detection module, a second comparator, and an amplitude and pulse-width modulator. The amplitude detection module calculates the amplitude signal according to the value of the digital signal. The second comparator compares the magnitude of the amplitude signal with a target value and generates a first comparison output signal and a second comparison output signal. The amplitude and pulse-width modulator generates an amplitude control signal and a pulse-width modulation signal according to the values of the first comparison output signal and the second comparison output signal, and then outputs the amplitude control signal to the digital-to-analog converter and outputs the pulse-width modulation signal to the drive module; wherein, the phase of the pulse-width modulation signal is in a 90° orthogonal relationship with the phase output by the charge-voltage conversion module.
[0013] Further, the digital-to-analog converter converts the amplitude control signal into an analog DC voltage signal and outputs it to the drive module.
[0014] Further, the driving module generates a square-wave pulse-width modulation signal according to the analog DC voltage signal and the pulse-width modulation signal, and inputs the square-wave pulse-width modulation signal to the driving capacitor; wherein, the square-wave pulse-width modulation signal is of the same frequency and phase as the pulse-width modulation signal.
[0015] Further, the charge pump module is used to generate a DC high voltage, and this DC high voltage is the high-voltage bias voltage of the MEMS gyroscope.
[0016] A driving method for a MEMS gyroscope, which is implemented through a MEMS gyroscope driving loop. The driving method includes: the charge-voltage conversion module converts the detected change in the driving detection capacitor into a differential voltage signal, the band-pass analog-to-digital converter converts the differential voltage signal into a digital signal, the first comparator converts the differential voltage signal into a square-wave signal, the phase-locked loop module generates a main clock signal according to the square-wave signal, the digital module generates an amplitude control signal and a pulse-width modulation signal according to the digital signal and the main clock signal, the digital-to-analog converter generates an analog DC voltage signal according to the amplitude control signal, the driving module generates a square-wave pulse-width modulation signal according to the analog DC voltage signal and the pulse-width modulation signal, and the driving capacitor drives the MEMS gyroscope according to the square-wave pulse-width modulation signal.
[0017] The beneficial effects of the present application are as follows: The MEMS gyroscope driving loop described in the present application includes a MEMS gyroscope part and a digital-analog hybrid circuit part. The charge-voltage conversion module C2V detects the change in the driving detection capacitor and converts this change into a differential voltage signal for output. The band-pass analog-to-digital converter BPADC converts the differential voltage signal into a digital signal. The phase-locked loop module PLL generates the working clock of the digital module DIG in the driving loop. The digital module DIG generates an amplitude control signal data and a pulse-width modulation signal pwm according to the digital signal adout from the band-pass analog-to-digital converter BPADC and the main clock signal clk m from the phase-locked loop module PLL. The pulse-width modulation signal pwm can be used as coarse adjustment, and the amplitude control signal data as fine adjustment; or the amplitude control signal data as coarse adjustment and the pulse-width modulation signal pwm as fine adjustment. The phase of the pulse-width modulation signal pwm is in a 90° orthogonal relationship with the phase output by the charge-voltage conversion module C2V. The driving module Driver generates square-wave pulse-width modulation signals acp and acn (driving signals) according to the analog DC voltage dc (DC signal) and the pulse-width modulation signal pwm, and acp and acn are of the same frequency and phase as the pwm signal. Therefore, the amplitudes and duty cycles of acp and acn can be adjusted simultaneously, so as to generate different driving forces to drive the MEMS gyroscope part. The combination of coarse and fine adjustments of the amplitude and duty cycle improves the modulation accuracy of the loop.
[0018] Adjusting the duty cycle of the square wave pulse width modulation signal directly adjusts the driving energy, and adjusting the amplitude of the square wave pulse width modulation signal further adjusts the AC value of the square wave pulse width modulation signal. The pulse width control of the square wave pulse width modulation signal is all completed by digital signal processing, with higher accuracy and reliability; the amplitude of the square wave pulse width modulation signal is also controlled by a digital signal processing circuit and then realized through the DAC part of the analog part. It neither requires an extra charge pump nor has a more efficient driving force, and the square wave pulse width modulation signal is not easily interfered by noise; at the same time, it also saves current, improves the driving efficiency and accuracy, and is more suitable for applications with low power consumption requirements in consumer electronics. Brief Description of the Drawings
[0019] Figure 1 It is a schematic structural diagram of the MEMS gyroscope driving loop in the embodiment of the present application;
[0020] Figure 2 It is a schematic structural diagram of the digital module DIG in the embodiment of the present application;
[0021] Figure 3 It is a schematic structural diagram of the driving capacitor and the driving detection capacitor in the MEMS gyroscope in the embodiment of the present application;
[0022] Figure 4 It is a schematic structural diagram of the phase-locked loop module PLL in the embodiment of the present application;
[0023] Figure 5 It is a schematic diagram of the phases of the square wave signal cmpo1 and the pulse width modulation signal pwm in the embodiment of the present application. Detailed Embodiment
[0024] The following is a clearer and more complete description of the specific implementation of the present application. Of course, the following description is only a part of the implementation of the present application, not all. Other methods derived from the embodiments of the present application all fall within the protection scope of the present application.
[0025] In the present application, the driving force of the MEMS gyroscope is determined by the product of an AC signal and a DC signal. The driving mechanism of the MEMS gyroscope needs to keep the oscillation amplitude of the MEMS gyroscope device itself unchanged. Among them, the DC signal hdc is fixed, so only the differential AC signal can be adjusted to change the driving force, so as to ensure that the oscillation amplitude of the MEMS gyroscope itself does not change with the change of environmental factors. The automatic amplitude control included in the driving loop detects and adjusts the amplitude and duty cycle of the two square wave pulse width modulation signals acp and acn at all times, so that even when the external environment such as temperature, stress, etc. changes, the oscillation amplitude of the MEMS gyroscope device itself remains unchanged.
[0026] Such as Figure 1As shown, the MEMS gyroscope drive loop includes a charge-voltage conversion module, a charge pump module, a first comparator, a phase-locked loop module, a drive module, a digital-to-analog converter, a digital module, and a band-pass analog-to-digital converter; one end of a pair of drive capacitors is equivalently connected in series with one end of a pair of drive detection capacitors, and the series connection point is biased at a high-voltage bias voltage and connected to the charge pump module; the other end of the pair of drive capacitors is connected to the drive module, and the other end of the pair of drive detection capacitors is connected to the charge-voltage conversion module; the output of the charge-voltage conversion module is input to the first comparator and the band-pass analog-to-digital converter, the output of the first comparator is input to the phase-locked loop module, the output of the phase-locked loop module is input to the digital module, the output of the band-pass analog-to-digital converter is input to the digital module, the output of the digital module is input to the digital-to-analog converter and the drive module, and the output of the digital-to-analog converter is input to the drive module.
[0027] The MEMS gyroscope drive method described in this application includes: the charge-voltage conversion module C2V converts the detected changes in the drive detection capacitors into differential voltage signals cvp and cvn, the band-pass analog-to-digital converter BPADC converts the differential voltage signals cvp and cvn into digital signals adout, the first comparator COMP1 converts the differential voltage signals cvp and cvn into a square wave signal cmpo1, and uses this square wave signal cmpo1 as the reference clock input to the phase-locked loop module. The phase-locked loop module PLL generates a high-speed main clock signal clk_m based on the square wave signal cmpo1. The digital module DIG generates an amplitude control signal data and a pulse-width modulation signal pwm based on the digital signal adout and the main clock signal clk_m. The digital-to-analog converter DAC generates an analog DC voltage signal dc based on the amplitude control signal data. The drive module Driver generates square wave pulse-width modulation signals acp and acn based on the analog DC voltage signal dc and the pulse-width modulation signal pwm. The drive capacitors drive the MEMS gyroscope based on the square wave pulse-width modulation signals acp and acn.
[0028] Among them, the structural schematic diagram of a pair of drive capacitors and a pair of drive detection capacitors of the MEMS gyroscope is as Figure 3 shown. The other two ends of the pair of drive capacitors are connected to the square wave pulse-width modulation signals acp and acn (i.e., drive signals), which are generated by the drive module (Driver); the other two ends (cip, cin) of the pair of drive detection capacitors are connected to the charge-voltage conversion module C2V.
[0029] It can be seen from Figure 1 that the driving force of the MEMS gyroscope is composed of the DC high-voltage signal hdc generated by the charge pump module CP and the AC signals acp and acn generated by the drive module Driver, that is, the product of AC and DC generates the driving force.
[0030] The DC high-voltage signal hdc generated by the charge pump module CP is configurable from 7V to 8V and is used to cooperate with different MEMS gyroscope device designs.
[0031] The charge-voltage conversion module C2V is used to detect the oscillation amplitude of the MEMS gyroscope. The band-pass analog-to-digital converter BPADC quantizes the oscillation amplitude of the charge-voltage conversion module C2V into a digital signal adout.
[0032] At the same time, the first comparator COMP1 converts the differential voltage signal of the charge-voltage conversion module C2V into a square-wave signal cmpo1, which is used as the reference clock input of the phase-locked loop module PLL.
[0033] As Figure 2 shown, the digital module DIG includes an amplitude detection module AMP Detector, a second comparator COMP2, and an amplitude and pulse-width modulator Level&PWM Modulator. The amplitude detection module calculates the amplitude signal according to the value of the digital signal. The second comparator compares the amplitude signal with the target value to generate a first comparison output signal and a second comparison output signal. The amplitude and pulse-width modulator generates an amplitude control signal data and a pulse-width modulation signal pwm according to the values of the first comparison output signal and the second comparison output signal, and then outputs the amplitude control signal data to the digital-to-analog converter DAC and outputs the pulse-width modulation signal pwm to the driver module Driver.
[0034] As Figure 4 shown, the phase-locked loop module PLL consists of a frequency-phase detector PFD, a charge pump and a low-pass filter module CP_LFP, a voltage-controlled oscillator VCO, and a divider DIVIDER. The division ratio of DIVIDER is 500. The operating frequency of the main clock signal clk_m of the digital module DIG is 500 times the frequency of the square-wave signal cmpo1, that is, 500 times the oscillation frequency of the MEMS gyroscope.
[0035] The digital module DIG generates a pulse-width modulation signal pwm and an amplitude control signal data.
[0036] As Figure 5 shown, the pulse-width modulation signal pwm and the square-wave signal cmpo1 clock signal are in a quadrature 90-degree relationship. The duty cycle of the pulse-width modulation signal pwm is adjustable in 5 gears, which are 50%, 40%, 30%, 20%, and 10% respectively. The control of the duty cycle is determined by the digital module DIG operating under the high-speed main clock signal clk_m.
[0037] The amplitude control signal data generates an analog DC voltage signal dc through a 7-bit digital-to-analog converter DAC. The analog DC voltage signal dc is continuously adjustable from 1V to 1.8V. The control of the analog DC voltage signal dc is also determined by the digital module DIG operating under the high-speed master clock signal clk m.
[0038] The charge-voltage conversion module C2V is a converter from capacitance change to voltage output. Therefore, to ensure that the oscillation amplitude of the MEMS gyroscope device itself remains unchanged, it is actually to ensure that the amplitudes of the differential voltage signals cvp and cvn output by the charge-voltage conversion module C2V remain unchanged. The digital signal adout is the quantization result of cvp and cvn through the band-pass analog-to-digital converter BPADC, that is, it is necessary to keep the digital signal adout and the amplitude signal amp output by the amplitude detection module AMP Detector unchanged.
[0039] When it is detected that the oscillation amplitude of the MEMS gyroscope becomes larger, the digital signal adout output by the band-pass analog-to-digital converter BPADC becomes larger, and the amplitude signal amp output by the amplitude detection module AMP Detctor also becomes larger accordingly. When the amplitude signal amp exceeds the target value target10LSB, the first comparison output signal cmpo21 output by the second comparator COMP2 changes from 0 to 1. At this time, it is considered that the amplitude signal amp exceeds the preset target value target. The amplitude and pulse-width modulation Level&PWM Modulator module reduces the duty cycle of the pulse-width modulation signal pwm by one level, and at the same time adjusts the amplitude value dc of the pulse-width modulation signal pwm (i.e., the analog DC voltage signal), thereby reducing the driving force. Specifically, the amplitude control signal data is adjusted from the maximum value to the minimum value until the first comparison output signal cmpo21 changes from 1 to 0 and then stops. If the amplitude control signal data is adjusted to the minimum value and the first comparison output signal cmpo21 is still 1, then continue to reduce the duty cycle of the pulse-width modulation signal pwm by one more level until the first comparison output signal cmpo21 changes from 1 to 0. Thus, the oscillation amplitude of the MEMS gyroscope is kept unchanged.
[0040] Conversely, when it is detected that the oscillation amplitude of the MEMS gyroscope becomes smaller, the digital signal adout output by the band-pass analog-to-digital converter BPADC becomes smaller, and the amplitude signal amp output by the amplitude detection module AMP Detector also becomes smaller accordingly. When the amplitude signal amp is less than the target value target10LSB, the second comparison output signal cmpo22 output by the second comparator COMP2 changes from 0 to 1. At this time, it is considered that the amplitude signal amp is lower than the preset target value target. The level and PWM modulator Level&PWM Modulator increases the duty cycle of the PWM signal pwm by one level and simultaneously adjusts the amplitude value dc of the PWM signal pwm, thereby reducing the driving force. Specifically, the amplitude control signal data is adjusted from the minimum value to the maximum value until the second comparison output signal cmpo22 changes from 1 to 0 and then stops. If the amplitude control signal data is adjusted to the maximum value and the second comparison output signal cmpo22 is still 1, then continue to increase the duty cycle of the PWM signal pwm by one level until the second comparator output signal cmpo22 changes from 1 to 0. Thus, the oscillation amplitude of the MEMS gyroscope is kept unchanged.
[0041] The above examples of the division ratio of the phase-locked loop module PLL, the five levels of the PWM signal pwm, the threshold value of 10LSB of the second comparator, and the adjustment range of the amplitude control signal data are just one implementation example. They can be correspondingly changed according to the actual precision control requirements and the parameters of the MEMS gyroscope device.
[0042] As can be seen from the above, this implementation mainly adjusts the driving force of the MEMS gyroscope through the differential square-wave PWM signals acp and acn whose amplitudes and duty cycles are both automatically adjustable, achieving precise adjustment of the driving force, so that the oscillation amplitude of the MEMS gyroscope does not change with the environment and other factors. After detecting a change in the oscillation amplitude of the MEMS gyroscope, first, the duty cycles of the square-wave PWM signals acp and acn are roughly adjusted, and then the driving amplitudes of the square-wave PWM signals acp and acn are finely adjusted; or first, the driving amplitudes of the square-wave PWM signals acp and acn are roughly adjusted, and then the duty cycles of the square-wave PWM signals acp and acn are finely adjusted; until the oscillation amplitude returns to the target value and remains unchanged.
[0043] The present invention is not limited to this implementation. For example, the square-wave amplitude can also be used for rough adjustment, and then the duty cycle of the square-wave signal is finely adjusted to achieve the adjustment of the driving force. Those of ordinary skill in the art can make changes, modifications, or variations to the above implementation within the scope of the present invention.
Claims
1. A MEMS gyroscope drive loop, the MEMS gyroscope comprising a pair of drive capacitors and a pair of drive detection capacitors, characterized in that: The driving loop includes a charge-voltage conversion module, a charge pump module, a first comparator, a phase-locked loop module, a driving module, a digital-to-analog converter, a digital module and a bandpass analog-to-digital converter; one end of a pair of driving capacitors is equivalently connected in series with one end of a pair of driving detection capacitors, and the series connection point is biased at a high-voltage bias voltage and connected to the charge pump module; the other end of the pair of driving capacitors is connected to the driving module, and the other end of the pair of driving detection capacitors is connected to the charge-voltage conversion module; the output of the charge-voltage conversion module is input to the first comparator and the bandpass analog-to-digital converter, the output of the first comparator is input to the phase-locked loop module, the output of the phase-locked loop module is input to the digital module, the output of the bandpass analog-to-digital converter is input to the digital module, the output of the digital module is input to the digital-to-analog converter and the driving module, and the output of the digital-to-analog converter is input to the driving module.
2. The MEMS gyroscope drive loop according to claim 1, wherein: The charge-to-voltage conversion module is used to detect the change of the driving detection capacitance and convert the change into a differential voltage signal, and then input the differential voltage signal to the first comparator and the bandpass analog-to-digital converter.
3. The MEMS gyroscope drive loop as claimed in claim 2, characterized in that: The first comparator converts the differential voltage signal into a square wave signal, and uses the square wave signal as a reference clock input of the phase-locked loop module.
4. The MEMS gyroscope drive loop as claimed in claim 3, characterized in that: The bandpass analog-to-digital converter quantizes the differential voltage signal to generate a digital signal which is input into the digital module.
5. The MEMS gyroscope drive loop as claimed in claim 4, characterized in that: The phase-locked loop module generates a main clock signal according to the square wave signal, and inputs the main clock signal to the digital module as the working main clock of the digital module.
6. The MEMS gyroscope drive loop as claimed in claim 5, characterized in that: The digital module includes an amplitude detection module, a second comparator, and an amplitude and pulse width modulator. The amplitude detection module calculates the amplitude signal according to the value of the digital signal. The second comparator compares the amplitude signal with the target value to generate a first comparison output signal and a second comparison output signal. The amplitude and pulse width modulator generates an amplitude control signal and a pulse width modulation signal according to the values of the first comparison output signal and the second comparison output signal, and then outputs the amplitude control signal to the digital-to-analog converter and outputs the pulse width modulation signal to the driving module; wherein the phase of the pulse width modulation signal is in a 90° orthogonal relationship with the phase output by the charge-to-voltage conversion module.
7. The MEMS gyroscope drive loop as claimed in claim 6, characterized in that: The digital-to-analog converter converts the amplitude control signal into an analog DC voltage signal and outputs it to the driving module.
8. The MEMS gyroscope drive loop as claimed in claim 7, characterized in that: The driving module generates a square wave pulse width modulation signal according to the analog DC voltage signal and the pulse width modulation signal, and inputs the square wave pulse width modulation signal to the driving capacitor; wherein the square wave pulse width modulation signal has the same frequency and phase as the pulse width modulation signal.
9. The MEMS gyroscope drive loop as claimed in claim 8, characterized in that: The charge pump module is used to generate a DC high voltage, which is a high voltage bias voltage of the MEMS gyroscope.
10. A MEMS gyroscope driving method, the driving method being implemented by the MEMS gyroscope driving loop according to any one of claims 1 to 9, characterized in that: The driving method comprises: a charge-voltage conversion module converts the detected change of the driving detection capacitor into a differential voltage signal, a bandpass analog-to-digital converter converts the differential voltage signal into a digital signal, a first comparator converts the differential voltage signal into a square wave signal, a phase-locked loop module generates a main clock signal according to the square wave signal, a digital module generates an amplitude control signal and a pulse width modulation signal according to the digital signal and the main clock signal, a digital-to-analog converter generates an analog direct current voltage signal according to the amplitude control signal, a driving module generates a square wave pulse width modulation signal according to the analog direct current voltage signal and the pulse width modulation signal, and a driving capacitor drives the MEMS gyroscope according to the square wave pulse width modulation signal; wherein the amplitude of the square wave pulse width modulation signal is roughly adjusted by the amplitude control signal, and the duty cycle of the square wave pulse width modulation signal is finely adjusted by the pulse width modulation signal; or when the amplitude of the square wave pulse width modulation signal is finely adjusted by the amplitude control signal, the duty cycle of the square wave pulse width modulation signal is roughly adjusted by the pulse width modulation signal.