阅读说明：本技术 一种小型化两次锁相的锁相环电路及方法 (Phase-locked loop circuit and method for miniaturization double phase locking ) 是由 杨宜生 白亮 李维亮 李振风 李墩泰 兰天 于 2019-11-12 设计创作，主要内容包括：本公开提供了一种小型化两次锁相的锁相环电路及方法,根据宽带VCO的输出频率计算出所需要的取样环的输入信号的设置频率,以及相应的分频电路、开关电路和各鉴相器的设置状态；进行第一次锁相,控制第一鉴相器和第一开关电路,将宽带VCO经过第三分频电路的分频信号输入第一鉴相器,与第二分频电路的输出信号进行相位比较,实现锁相环的快速锁定,进行第二次锁相,根据输出频率值确定第二开关电路和第三开关电路的输出信号,将倍频电路的输出信号与宽带VCO的反馈信号在混频器中进行混频,根据差频得到的信号范围进行各开关电路的切换,实现锁相。(The utility model provides a phase-locked loop circuit and a method for miniaturization and double phase locking, which calculate the setting frequency of the input signal of a sampling loop according to the output frequency of a broadband VCO, and the setting states of a corresponding frequency division circuit, a switch circuit and each phase discriminator; and performing first phase locking, controlling the first phase detector and the first switch circuit, inputting a frequency division signal of the broadband VCO passing through the third frequency division circuit into the first phase detector, performing phase comparison with an output signal of the second frequency division circuit to realize rapid locking of the phase-locked loop, performing second phase locking, determining output signals of the second switch circuit and the third switch circuit according to an output frequency value, performing frequency mixing on an output signal of the frequency doubling circuit and a feedback signal of the broadband VCO in a mixer, and switching each switch circuit according to a signal range obtained by difference frequency to realize phase locking.)

1. A phase-locked loop circuit of miniaturized two-time phase locking is characterized in that: including sample ring, a plurality of frequency division circuit, multiplier circuit, mixer and switch circuit, wherein:

the sampling loop is used for receiving an input signal and transmitting the input signal to the first frequency division circuit, the frequency multiplication circuit and the second frequency division circuit, the first frequency division circuit is connected with the first frequency mixer, the frequency multiplication circuit is connected with the second frequency mixer, the first frequency mixer mixes an output signal of the second frequency mixer with an output signal of the first frequency division circuit and enters the second phase discriminator to obtain a feedback signal required by the second phase discrimination;

the second mixer mixes frequency of frequency multiplication signals of the broadband VCO and the sampling ring input signals, a difference frequency signal of the frequency multiplication signals is obtained, the broadband VCO simultaneously enters a third frequency division circuit, and the frequency division signal and a signal of the second frequency division circuit enter a first phase discriminator to serve as a feedback signal of first phase discrimination;

a first switch circuit is arranged between the first phase discriminator and the second phase discriminator to realize the switching of the first phase discrimination and the second phase discrimination, and the loop filter carries out filtering processing on the output voltage of each phase discriminator to reduce the influence of ripple voltage on output signals and is connected with a broadband VCO to output signals.

2. A miniaturized double-locked phase-locked loop circuit as claimed in claim 1, characterized in that: and a second switch circuit is arranged between the first mixer and the second mixer so as to select whether the second mixing of the first mixer is needed or not.

3. A miniaturized double-locked phase-locked loop circuit as claimed in claim 1, characterized in that: and a third switch circuit is connected between the second switch circuit and the first mixer and used for selecting the output signal of the first mixer or the second mixer to the second phase discriminator.

4. A miniaturized double-locked phase-locked loop circuit as claimed in claim 1, characterized in that: the sampling ring is connected with a phase-locked loop circuit to receive an input signal which is generated by the phase-locked loop circuit and has a frequency range of 3.2 GHz-3.25 GHz.

5. A miniaturized double-locked phase-locked loop circuit as claimed in claim 1, characterized in that: the first frequency dividing circuit performs frequency division processing on an output signal of an input signal, and can generate frequency division signals of 1/2, 1/4, 1/8 and 1/16 according to control;

or, the second frequency dividing circuit is a 32 frequency dividing point circuit, and performs 32 frequency division on the sampling ring input signal to generate a reference signal;

or, the third frequency dividing circuit is a frequency dividing circuit of 4.

6. A miniaturized double-locked phase-locked loop circuit as claimed in claim 5, characterized in that: the first phase discriminator is used for discriminating the phase for the first time, and comparing the phase of the frequency division signal output by the frequency division circuit 4 with the phase of the reference signal generated by the frequency division circuit 32;

or the second phase detector is used for carrying out phase detection for the second time and carrying out phase comparison on the output phase detection signal of the third switching circuit of the switching circuit and the reference signal generated by the 32-frequency division circuit.

7. Method of operating a circuit according to any of claims 1-6, characterized in that: the method comprises the following steps:

calculating the setting frequency of the input signal of the required sampling ring and the setting states of the corresponding frequency division circuit, the switching circuit and each phase discriminator according to the output frequency of the broadband VCO;

performing first phase locking, controlling the first phase detector and the first switch circuit, inputting the frequency division signal of the wideband VCO passing through the third frequency division circuit into the first phase detector, performing phase comparison with the output signal of the second frequency division circuit to realize rapid locking of the phase-locked loop,

and performing secondary phase locking, determining output signals of the second switch circuit and the third switch circuit according to the output frequency value, mixing the output signal of the frequency doubling circuit and a feedback signal of the broadband VCO in a mixer, and switching each switch circuit according to a signal range obtained by difference frequency to realize phase locking.

8. The method of claim 7, further comprising: if the signal obtained by the difference frequency is larger than the set value, the signal is continuously mixed with the output signal of the first frequency dividing circuit in the first mixer to obtain a difference frequency signal serving as a phase discrimination signal of the second phase discriminator, and the whole phase-locked loop is realized by switching the first switch circuit.

9. The method of claim 7, further comprising: and if the difference frequency signal output by the second mixer is smaller than the set value, the difference frequency signal is directly output to the phase discrimination signal of the second phase discriminator through the second switch circuit and the third switch circuit.

10. The method of claim 7, further comprising: the range of the final output local oscillation signal is 5GHz to 10.4 GHz.

Technical Field

The disclosure belongs to the technical field of phase-locked loop circuit design, and relates to a miniaturized phase-locked loop circuit and a method for twice phase locking.

Background

The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.

The phase-locked loop is a necessary means for generating high-purity signals, has a very wide application range, is applied to the fields of radar system testing, satellite communication, navigation, quantum computing and the like, and is an essential component in a modern electronic system. With the continuous development of electronic technology, various electronic systems have put higher and higher requirements on main performance indexes of test signals, such as frequency resolution, phase noise, spurious signals, frequency range and the like. And when a satellite communication system and a radar T/R component test system are constructed, hundreds of paths of generated signals are often needed, which puts high requirements on the volume and the cost of a phase-locked loop.

The current main phase-locked loop design technologies mainly include: direct frequency synthesis techniques, phase-locked loop frequency synthesis techniques, and direct digital frequency synthesis techniques.

The direct frequency synthesis technology generally uses one or more high-stability and high-purity crystal reference sources to perform addition, subtraction, multiplication and division operations through frequency multiplication, frequency division and frequency mixing technologies to generate various frequencies, and then uses an electronic switch to select and output the required frequency.

The phase-locked loop frequency synthesis technology mainly comprises a voltage-controlled oscillator, a phase discriminator, a variable frequency divider and a loop filter. The output signal of the voltage-controlled oscillator is compared with the phase of the reference signal in the phase discriminator after passing through the variable frequency divider. When the voltage-controlled oscillator generates frequency drift, the control voltage output by the phase discriminator changes, so that the frequency of the voltage-controlled oscillator is always locked on the reference frequency of N times. The signal frequency range that this kind of design produced is wide, and circuit structure is simple, and is small, but because frequency division number of times is too much, causes output signal phase noise to worsen, can't satisfy high performance test system's demand.

The direct digital frequency synthesis technology is a new technology which introduces advanced digital processing theory and method into the signal synthesis field. It mainly comprises five parts: a reference clock, a phase accumulator, a sine lookup table, a D/a converter and a low pass filter. The basic working principle is that according to the generation of a sine function, different phases are used for giving different voltage amplitudes from the phase angle, and the required waveform can be obtained through smoothing processing of a low-pass filter. The signal phase noise generated by the design method is low, the frequency switching time is fast, but the stray signal is often introduced to the near end of the signal, and the use of the test signal is influenced.

According to the inventor, in the existing broadband phase-locked loop circuit, a common phase-locked loop scheme is mostly built by adopting an integrated phase-locked loop chip and a special VCO (voltage controlled oscillator), and the broadband phase-locked loop circuit has the characteristics of simple circuit structure, low power consumption and the like, but the frequency band is high, the frequency range is wide, and the phase noise cannot achieve a good effect.

In order to achieve high frequency resolution, a fractional frequency division loop is often used to phase-lock a reference signal of a main loop, and a wideband VCO output signal is frequency-divided to obtain a signal serving as a feedback phase discrimination signal.

The direct digital frequency synthesis technology is limited by the highest clock frequency available for the device, the output frequency is not high enough to generate the output signal frequency of the radio frequency band, and the use of the DAC device essential in the technology causes more spurious signals to be generated in the output signal of the DAC device, which affects the signal quality.

Disclosure of Invention

The phase-locked loop circuit and the method have the advantages that the phase-locked loop circuit is realized by utilizing the broadband VCO chip, extremely low phase noise is realized, meanwhile, a decimal frequency division ring is omitted in design, the number of adopted devices is greatly reduced, the space of a PCB is saved, the signal purity is ensured, the debugging difficulty is reduced, and the power consumption is reduced.

According to some embodiments, the following technical scheme is adopted in the disclosure:

a phase-locked loop circuit of miniaturized two-time phase locking comprises a sampling loop, a plurality of frequency division circuits, a frequency multiplication circuit, a frequency mixer and a switch circuit, wherein:

the sampling loop is used for receiving an input signal, transmitting the input signal to the first frequency division circuit, the frequency multiplication circuit and the second frequency division circuit after multiple power division, the first frequency division circuit is connected with the first frequency mixer, the frequency multiplication circuit is connected with the second frequency mixer, the first frequency mixer mixes an output signal of the second frequency mixer with an output signal of the first frequency division circuit, and the output signal enters the second phase discriminator to obtain a feedback signal required by the second phase discrimination;

the second mixer mixes frequency of frequency multiplication signals of the broadband VCO and the sampling ring input signals, a difference frequency signal of the frequency multiplication signals is obtained, the broadband VCO simultaneously enters a third frequency division circuit, and the frequency division signal and a signal of the second frequency division circuit enter a first phase discriminator to serve as a feedback signal of first phase discrimination;

a first switch circuit is arranged between the first phase discriminator and the second phase discriminator to realize the switching of the first phase discrimination and the second phase discrimination, a loop filter carries out filtering processing on the output voltage of each phase discriminator, the influence of ripple voltage on output signals is reduced, and the loop filter is connected with a broadband VCO to control the output signals.

As an alternative embodiment, a second switch circuit is disposed between the first mixer and the second mixer to select whether the second mixing of the first mixer is required.

As an alternative implementation, a third switching circuit is connected between the second switching circuit and the first mixer, and is used to select the output signals of the first mixer and the second mixer to the second phase detector.

As an alternative embodiment, the sampling loop is connected to a phase locked loop circuit to receive an input signal generated by the phase locked loop circuit in a frequency range of 3.2GHz to 3.25 GHz.

As an alternative embodiment, the first frequency-dividing circuit performs frequency-dividing processing on the output signal of the input signal, and is capable of generating frequency-divided signals of 1/2, 1/4, 1/8, 1/16 according to control.

In an alternative embodiment, the second frequency dividing circuit is a 32-point frequency dividing circuit, which divides the sampling loop input signal by 1/32 to generate the reference signal.

As an alternative embodiment, the third divide-by-4 circuit.

In an alternative embodiment, the first phase detector is used for detecting the phase of the first time, and compares the phase of the frequency-divided signal output by the frequency-dividing-by-4 circuit with the phase of the reference signal generated by the frequency-dividing-by-32 circuit.

In an alternative embodiment, the second phase detector is used for phase detection for the second time, and phase comparison is performed between the output phase detection signal of the third switching circuit of the switching circuit and the reference signal generated by the frequency division circuit of 32.

The working method based on the circuit comprises the following steps:

firstly, calculating the required input signal frequency of a sampling ring and the setting states of a corresponding frequency division circuit, a switch circuit and each phase discriminator according to the output frequency of a broadband VCO;

and performing first phase locking, controlling the first phase detector and the first switch circuit, inputting a frequency division signal of the broadband VCO passing through the third frequency division circuit into the first phase detector, and performing phase comparison with an output signal of the second frequency division circuit to realize rapid locking of the phase-locked loop.

And performing secondary phase locking, determining output signals of the second switch circuit and the third switch circuit according to the output frequency value, mixing the output signal of the frequency doubling circuit and a feedback signal of the broadband VCO in a mixer, and switching each switch circuit according to the signal frequency obtained by difference frequency to realize secondary phase locking.

As an alternative implementation, if the signal obtained by the difference frequency is greater than the set phase detection frequency value, the signal continues to be mixed with the output signal of the first frequency dividing circuit in the first mixer, so as to obtain the difference frequency signal as the phase detection signal of the second phase detector, and the whole phase-locked loop is realized through the switching of the first switch circuit.

As an alternative embodiment, if the difference frequency signal output by the second mixer is within the set range of the phase detection frequency value, the difference frequency signal directly passes through the second switch circuit and the third switch circuit and is output to the phase detection signal of the second phase detector.

As an alternative embodiment, the final output local oscillator signal range is 5GHz to 10.4 GHz.

Compared with the prior art, the beneficial effect of this disclosure is:

the design method adopts two phase detectors to lock the phase in sequence, firstly utilizes the frequency division signal of the local oscillator signal to directly design a phase locking circuit, and then switches the phase detectors through a switch to enable the harmonic waves of the local oscillator signal and the reference signal to carry out frequency mixing and then lock the phase, thereby realizing the output of low-noise broadband signals.

The reference signals of the two phase discriminations are generated by the same signal, so that the miniaturization design of the circuit is realized, and the signal purity is ensured.

The design circuit is realized on the PCB, and the occupied area of all circuits is small. The power supply and control signals are connected with the PCB through the feed-through capacitor, and the middle part of the power supply and control signals is separated by the metal cavity, so that the interference of the power supply to microwave signals is effectively reduced, the performance index of output signals is improved, the circuit structure is compact, and the integration degree is high. And a cavity isolation processing mode is adopted in the design, so that the radiation of stray signals can be effectively inhibited.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.

Fig. 1 is a schematic structural diagram of the present disclosure.

The specific implementation mode is as follows:

the present disclosure is further described with reference to the following drawings and examples.

It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.

It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof, unless the context clearly indicates otherwise.

As described in the background art, in the existing phase-locked loop circuit design technology, a designed phase-locked loop circuit often needs to have the characteristics of small frequency step, wide frequency range, low phase noise and the like, and in order to meet the requirement, a plurality of phase-locked loops such as a fractional loop, a sampling loop, a broadband phase-locked loop and the like are often needed to be designed so as to ensure that the performance index of an output local oscillation signal can meet the requirement of the overall index. Due to the wide output frequency range and the high operating frequency, a wideband YTO or wideband VCO chip is required. The former has large volume and high power consumption, is not beneficial to debugging work, and cannot be placed in a miniaturized portable test system. The broadband integrated VCO is small in size and simple in working mode, but the phase noise index of the broadband integrated VCO is not ideal enough, and a simple phase-locked loop design circuit cannot achieve high performance index.

In order to solve the problems, the phase-locked loop circuit of the miniaturized double phase locking is realized by utilizing a broadband VCO chip, the output frequency range is 5GHz to 10.4GHz, and the phase noise of a 10.4GHz signal can reach-121 dBc/Hz @10 kHz. When the extremely low phase noise is realized, a decimal frequency division ring is omitted in the design, the number of adopted devices is greatly reduced, the PCB space is saved, the signal purity is ensured, the debugging difficulty is reduced, and the power consumption is reduced.

A wide-band phase-locked loop circuit with two phase locks is disclosed, as shown in figure 1, the circuit needs few components, and has simple structure, small volume and high performance index. The circuit divides the input sampling ring signal (3.2 GHz-3.25 GHz) into two paths, one path is divided by 32 to obtain a high-purity signal about 100MHz, and the high-purity signal is used as a reference signal shared by two phase locks. And after frequency division and frequency multiplication are carried out on the other path of sampling loop signal, various harmonic signals can be generated, and the signal is used for carrying out frequency mixing with a feedback signal of the broadband VCO to obtain a phase discrimination signal. The phase-locked loop comprises 2 phase detectors which are respectively used for completing two phase locking processes. During the first phase locking, the four-frequency-division signal of the broadband VCO directly enters a phase discriminator to form a phase-locked loop with a reference signal, so that the loop is quickly locked. The phase noise of the output signal is poor at this time because the frequency division ratio is high. And then, the phase detector is quickly switched to another phase detector, and simultaneously, the output signal of the broadband VCO and the harmonic wave of the sampling loop signal are mixed to finally obtain a feedback signal about 50 MHz. The feedback signal of the second phase locking process is obtained by a frequency mixing mode, so that the phase noise of the output signal can be greatly optimized.

As shown in fig. 1, the circuit specifically comprises a sampling loop input signal 1, a frequency dividing circuit 2, a frequency multiplying circuit 3, a frequency dividing circuit 4 of 32, a mixer 5, a mixer 6, a switching circuit 7, a switching circuit 8, a frequency dividing circuit 9 of 4, a phase detector 10, a phase detector 11, a switching circuit 12, a loop filter 13, a wideband VCO14, and the like.

The sampling loop input signal 1 is generated by a phase-locked loop circuit, and the frequency range is 3.2 GHz-3.25 GHz; the frequency dividing circuit 2 performs frequency division processing on the output signal of the sampling loop input signal 1, and can generate frequency division signals of 1/2, 1/4, 1/8 and 1/162 according to control; the frequency multiplier circuit 3 is a step diode and can generate integral multiple harmonic waves of the sampling loop input signal. The divide-by-32 circuit 4 divides the sampling loop input signal 1 by 32 times to generate a reference signal of about 100 MHz. The frequency mixer 5 mainly mixes the output signal of the frequency mixer 6 with the output signal of the frequency dividing circuit 2 to obtain a feedback signal required by the second phase discrimination; the mixer 6 mixes the frequency multiplication signals of the broadband VCO14 and the sampling loop input signal 1 and takes the difference frequency signals; the switching circuit 7 selects whether to perform second frequency mixing with the frequency mixer 5; the switching circuit 8 is used for selecting the output signal of the mixer 5 or the mixer 6 to the phase detector 10; the 4-frequency division circuit 9 performs 4-frequency division processing on the feedback signal of the broadband VCO14 to serve as the feedback signal of the first phase discrimination; the phase detector 10 is used for performing phase detection for the second time, and performing phase comparison on an output phase detection signal of the switching circuit 8 and a reference signal generated by the frequency division circuit 4 of 32; the phase detector 11 is used for performing phase detection for the first time, and performing phase comparison on a frequency division signal output by the frequency division circuit 4 9 and a reference signal generated by the frequency division circuit 4 of 32; the switching circuit 12 is used to perform the switching between the first phase detection and the second phase detection. The loop filter 13 performs filtering processing on the output voltage of the phase discriminator, reduces the influence of ripple voltage on the output signal, and ensures the stability of the loop when the switching circuit 12 switches; the output frequency of the broadband VCO14 is 5 GHz-10.4 GHz, and the broadband VCO has the characteristics of wide frequency band and low noise.

The working principle is as follows:

firstly, the upper computer calculates the required output frequency of the sampling loop signal 1 according to the output frequency of the wideband VCO14, and the setting of the frequency division ratio of the corresponding frequency division circuit 2, the setting states of the switch circuit 7, the switch circuit 8, the phase detector 10 and the phase detector 11. After the output frequency of the sampling loop signal 1 is set, the phase locking process is started for two times: during the first phase locking, the phase detector 11 and the switch circuit 12 are controlled, the frequency division signal of the broadband VCO14 passing through the frequency division circuit 9 4 is input into the phase detector 11, and the phase comparison is carried out on the frequency division signal and the output signal of the frequency division circuit 4 32, so that the fast locking of the phase-locked loop is realized, and the phase noise of the output local oscillation signal is poor due to the large frequency division ratio; and then, performing second phase locking, determining output signals of the switch circuit 7 and the switch circuit 8 according to the output frequency value, mixing the output signal of the frequency doubling circuit 3 and a feedback signal of the broadband VCO14 in the mixer 6, if the signal obtained by difference frequency is greater than 100MHz, continuing to perform mixing processing with the output signal of the frequency dividing circuit 2 in the mixer 5 to obtain a difference frequency signal serving as a phase detection signal of the phase detector 10, and switching through the switch circuit 12 to realize the whole phase-locked loop. If the difference frequency signal output by the mixer 6 is less than 100MHz, the difference frequency signal is directly output to the phase detector 10 through the switch circuit 7 and the switch circuit 8. The final output local oscillator signal range is 5 GHz-10.4 GHz, and the method has the advantages of low phase noise, low stray and the like, and meanwhile, reference signals used by two phase discriminations are generated by frequency division of sampling signals, so that the miniaturization design of a circuit is realized, and the signal purity is ensured.

The design circuit is realized on a PCB (printed Circuit Board), the board material of the PCB is Rogers4350B, and all circuits only occupy the area of 16cm multiplied by 9 cm. The power supply and the control signal are connected with the PCB through the core-through capacitor, and the middle part of the power supply and the control signal is separated by the metal cavity, so that the interference of the power supply to the microwave signal is effectively reduced, and the performance index of the output signal is improved.

In conclusion, the output frequency range of the local oscillation signal output by the circuit is wide, can reach 5GHz to 10.4GHz, and can meet the requirements of various applications.

The output local oscillation signal has low phase noise, the phase noise of the local oscillation signal of 10.4GHz at the frequency offset of 10kHz can be lower than-121 dBc/Hz, and the test requirement of a high-performance signal source can be met.

The circuit structure is compact, and the integration degree is high. And a processing mode of cavity isolation is adopted, so that the radiation of stray signals can be effectively inhibited.

As will be appreciated by one skilled in the art, embodiments of the present disclosure may be provided as a method, system, or computer program product. Accordingly, the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present disclosure may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and so forth) having computer-usable program code embodied therein.

The present disclosure is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the disclosure. It will be understood that each flow and/or block of the flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Although the present disclosure has been described with reference to specific embodiments, it should be understood that the scope of the present disclosure is not limited thereto, and those skilled in the art will appreciate that various modifications and changes can be made without departing from the spirit and scope of the present disclosure.