Sine wave phase-locked loop circuit and system realized by using frequency traction effect, and oscilloscope

Abstract

The invention discloses a sine wave phase-locked loop circuit realized by using a frequency traction effect, a system and an oscilloscope. The sine wave phase-locked loop circuit comprises an oscillator, a phase loop, an amplitude loop, an analog multiplier and a coupling network, the phase loop comprises a phase discriminator, a first proportional integral circuit and a voltage-controlled oscillator, and the amplitude loop comprises a detection circuit and a second proportional integral circuit; signals output by the phase loop and the amplitude loop are multiplied through an analog multiplier to obtain waveforms with frequency and amplitude adjusted, and the waveforms are coupled into the oscillator through a coupling network to pull the frequency of the oscillator. The sine wave phase-locked loop circuit provided by the invention can output sine waves which are very low in harmonic component and have no error between the phase and the amplitude and the preset value of the microcontroller, and can be used for designing a stable trigger circuit and an efficient spectrum analysis function for a virtual oscilloscope, so that the cost is greatly reduced. The phase-locked loop circuit can be widely applied to the technical field of phase-locked loop circuits.

Description

Technical Field

[0001] The present invention relates to the technical field of phase-locked loop circuits, and in particular to a sine wave phase-locked loop circuit, system and oscilloscope realized by utilizing a frequency pulling effect. Background Art

[0002] Electronic information is a subject that places great emphasis on practice. Professional learners and amateurs need to perform a lot of practical operations to master the technology. Usually, electronic information technology experiments have a great demand for instruments such as oscilloscopes, logic analyzers, spectrum analyzers, signal generators, etc. However, these professional instruments are often expensive, and it is difficult for professional learners and amateurs who are just starting out to purchase such instruments.

[0003] At the same time, some professional learners and amateurs may want to DIY virtual experimental instruments. However, such virtual instruments often adopt highly integrated solutions, which is not conducive to learners and amateurs to learn their principles. There is a lack of solutions on the market to reduce the cost of these virtual experimental instruments, and to ensure the accuracy of virtual instruments as much as possible while assembling and modifying them by hand.

[0004] Therefore, it is necessary to study a circuit design scheme for a virtual oscilloscope that is low-cost, can be assembled and modified by oneself, does not increase the volume and weight, and improves the accuracy as much as possible. This circuit applied to the virtual oscilloscope includes the functions of waveform and spectrum analysis, and professional learners and amateurs can also customize its operation logic in their host computer. Summary of the invention

[0005] In order to solve at least one of the technical problems existing in the prior art to a certain extent, the object of the present invention is to provide a sinusoidal wave phase-locked loop circuit, system and oscilloscope realized by using the frequency pulling effect.

[0006] The first technical solution adopted by the present invention is:

[0007] A sine wave phase-locked loop circuit realized by frequency pulling effect, comprising an oscillator, a phase loop, an amplitude loop, an analog multiplier and a coupling network; the phase loop comprises a phase detector, a first proportional integral circuit and a voltage-controlled oscillator, and the amplitude loop comprises a detection circuit and a second proportional integral circuit;

[0008] The sine wave generated by the oscillator is input into the phase loop and the amplitude loop respectively;

[0009] In the phase loop, the phase detector compares the phase information of the sine wave with the reference signal, and inputs the comparison result into the first proportional integral circuit for calculation, and the calculation output of the first proportional integral circuit is used to fine-tune the frequency of the voltage-controlled oscillator;

[0010] In the amplitude loop, the detection circuit compares the amplitude information of the sine wave with the preset PWM signal, and inputs the comparison result into the second proportional integration circuit;

[0011] The frequency-adjustable waveform generated by the voltage-controlled oscillator and the output of the second proportional-integral circuit are multiplied by an analog multiplier to obtain a waveform with regulated frequency and amplitude. The waveform is coupled into the oscillator through a coupling network to pull the frequency of the oscillator.

[0012] Furthermore, the oscillator is an RC oscillator or an LC oscillator.

[0013] Furthermore, the detection circuit is replaced by a rectification circuit.

[0014] Furthermore, the sinusoidal wave phase-locked loop circuit also includes a pre-filter, and the pre-filter is connected between the analog multiplier and the coupling network.

[0015] Furthermore, the sinusoidal signal output by the sinusoidal phase-locked loop circuit is multiplied by the external input signal and filtered to obtain the frequency component of the external input signal.

[0016] Furthermore, the capture range of the sinusoidal phase-locked loop circuit can be controlled to be roughly adjusted to quickly lock with the fundamental wave or specific subharmonic of the external input signal to obtain a trigger signal synchronized with the fundamental wave or specific subharmonic of the external input signal.

[0017] Further, the reference signal is a reference square wave outputted by the microcontroller; the preset PWM signal is a PWM signal outputted by the microcontroller;

[0018] A control point is added to the frequency selection network of the oscillator, and the values ​​of the nonlinear resistor, capacitor and inductor are changed by outputting a PWM signal through a microcontroller, so as to roughly adjust the resonant frequency of the oscillator to achieve coarse frequency adjustment.

[0019] The second technical solution adopted by the present invention is:

[0020] A system includes two sine wave phase locked loop circuits as described above, the two sine wave phase locked loop circuits output two sinusoidal signals with a phase difference of 90 degrees, which are used to obtain the sine component and cosine component of the frequency component of the external input signal.

[0021] The third technical solution adopted by the present invention is:

[0022] An oscilloscope using a spectrum analysis circuit comprises the sine wave phase-locked loop circuit as described above.

[0023] The fourth technical solution adopted by the present invention is:

[0024] An oscilloscope using a trigger circuit comprises the sine wave phase-locked loop circuit as described above.

[0025] The beneficial effects of the present invention are as follows: the sinusoidal phase-locked loop circuit proposed in the present invention can output a sinusoidal wave with very low harmonic components and phase and amplitude with no error with the preset values ​​of the microcontroller, and can be used to design a stable trigger circuit and efficient spectrum analysis function for a virtual oscilloscope, thereby greatly reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the embodiments of the present invention or the drawings of related technical solutions in the prior art are introduced below. It should be understood that the drawings introduced below are only for the convenience of clearly describing some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0027] Figure 1 It is a structural block diagram of a sinusoidal phase-locked loop implemented by utilizing the frequency pulling effect in an embodiment of the present invention.

[0028] Figure 2 It is a circuit diagram of several modules including an analog multiplier, a prefilter, a coupling network, an LC oscillator, a detection circuit, and a filter in a virtual oscilloscope spectrum analysis circuit realized by using the frequency pulling effect in an embodiment of the present invention.

[0029] Figure 3 In the embodiment of the present invention, Figure 1 Structural block diagram of the virtual oscilloscope trigger circuit of the sine wave phase-locked loop.

[0030] Figure 4 In the embodiment of the present invention, control Figure 3 Flowchart of the embedded program of the virtual oscilloscope trigger circuit shown in .

[0031] Figure 5 In the embodiment of the present invention, Figure 1 The structural block diagram of the virtual oscilloscope spectrum analysis circuit of the sine wave phase-locked loop.

[0032] Figure 6 In the embodiment of the present invention, control Figure 5 Flowchart of the embedded program of the virtual oscilloscope spectrum analysis circuit shown in . DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limitations of the present invention. For the step numbers in the following embodiments, they are only provided for the convenience of explanation, and the order between the steps is not limited in any way, and the execution order of each step in the embodiment can be adaptively adjusted according to the understanding of those skilled in the art.

[0034] In the description of the present invention, it should be understood that descriptions involving orientations, such as up, down, front, back, left, right, etc., and orientations or positional relationships indicated are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0035] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed" etc. are understood as not including the number itself, and "above", "below", "within" etc. are understood as including the number itself. If there is a description of "first" or "second", it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0036] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0037] In view of the existing technical problems, the present invention provides a low-cost, modular virtual oscilloscope that can be assembled and modified by learners and amateurs. Its trigger circuit and spectrum analysis function adopt Figure 1 The circuit structure shown has a spectrum analysis error as low as 200Hz / 1MHz. The core structure of the virtual oscilloscope circuit involved in the present invention is three sine wave phase-locked loops realized by using the frequency pulling effect. Two of the sine wave phase-locked loops are used for spectrum analysis, and one sine wave phase-locked loop is used for a more stable trigger function.

[0038] like Figure 1 As shown, this embodiment provides a sine wave phase-locked loop circuit realized by using the frequency pulling effect, including an oscillator, a phase loop, an amplitude loop, an analog multiplier and a coupling network; the phase loop includes a phase detector, a first proportional integration circuit and a voltage-controlled oscillator, and the amplitude loop includes a detection circuit and a second proportional integration circuit;

[0039] The sine wave generated by the oscillator is input into the phase loop and the amplitude loop respectively;

[0040] In the phase loop, the phase detector compares the phase information of the sine wave with the reference signal, and inputs the comparison result into the first proportional integral circuit for calculation, and the calculation output of the first proportional integral circuit is used to fine-tune the frequency of the voltage-controlled oscillator;

[0041] In the amplitude loop, the detection circuit compares the amplitude information of the sine wave with the preset PWM signal, and inputs the comparison result into the second proportional integration circuit;

[0042] The frequency-adjustable waveform generated by the voltage-controlled oscillator and the output of the second proportional-integral circuit are multiplied by an analog multiplier to obtain a waveform with regulated frequency and amplitude. The waveform is coupled into the oscillator through a coupling network to pull the frequency of the oscillator.

[0043] Reference Figure 1 , the low harmonic sine wave generated by the oscillator is sent to the phase loop and the amplitude loop for phase discrimination and detection respectively to obtain the phase and amplitude information of the sine wave. The phase information will be compared with the phase of the reference square wave output from the microcontroller, and the amplitude information will be compared with the PWM signal output by the microcontroller, and the PID algorithm will be calculated by the proportional integral circuit. The output of the proportional integral circuit of the phase loop will be used to fine-tune the frequency of the voltage-controlled oscillator. The frequency-adjustable waveform generated by the voltage-controlled oscillator will be multiplied by the output of the proportional integral circuit of the amplitude loop to obtain a waveform with both frequency and amplitude adjusted. After that, the waveform is coupled into the oscillator through the coupling network to pull the frequency of the oscillator. Although all signal processing links before the coupling network contain a large number of nonlinear effects, the harmonics generated by them are partially filtered out when passing through the coupling network, and the harmonics do not resonate with the oscillator and cannot be enhanced by positive feedback. Therefore, the sine wave phase-locked loop can output a sine wave with very low harmonic components, and the phase and amplitude have no error with the preset values ​​of the microcontroller, which can be used to design a stable trigger circuit and efficient spectrum analysis function for a virtual oscilloscope.

[0044] As an optional implementation, the oscillator is an RC oscillator or an LC oscillator.

[0045] In some embodiments, in the above-mentioned oscillator, the total positive feedback gain of the loop of the oscillator should be slightly less than 1. At this time, when the voltage-controlled oscillator does not output a signal, the oscillator will perform attenuated oscillation. When the voltage-controlled oscillator outputs a small signal whose harmonic components are difficult to eliminate, the small signal will be superimposed on the fed-back sine wave, causing the oscillator to generate forced vibration and output a large signal with low harmonics.

[0046] Since a multi-stage frequency selection network is used in the feedback loop of the RC or LC oscillator, the frequency characteristic of the oscillator is very steep, and large-scale frequency control cannot be achieved by frequency pulling alone. Therefore, a control point can be added to the frequency selection network of the oscillator, and the values ​​of nonlinear resistance, capacitance, and inductance can be changed by outputting a PWM signal through a microcontroller, so as to roughly adjust the resonant frequency of the oscillator, and ensure that within the frequency adjustment range of the voltage-controlled oscillator of the phase loop, the RC or LC oscillator can have a relatively flat amplitude-frequency characteristic. At the same time, the PWM signal output by the microcontroller for coarse frequency adjustment will also roughly adjust the pre-filter of the coupling network and the voltage-controlled oscillator.

[0047] The following combination Figure 2 The sine wave phase-locked loop circuit is supplemented with descriptions of specific implementation methods. Figure 2 In the circuit, the microcontroller outputs a frequency-adjustable square wave to it, and performs coarse frequency and amplitude adjustment on it through the PWM signal. The circuit can generate a sine wave locked with the input square wave and output its amplitude. When an external signal is input, the circuit can obtain the average value of the product of the external signal and the sine wave described above. The ratio of the average value of the product to the amplitude of the sine wave reflects the component of the external input signal at the current frequency.

[0048] like Figure 2 As shown, in the LC oscillation circuit, let the voltage gain of the amplifier circuit composed of C4, R1, R2, Q2, R3, and R4 be A1, and the ratio of its input voltage to the output voltage of the amplifier circuit where Q1 is located is p1. Let the voltage gain of the amplifier circuit composed of C2, R5, R6, Q1, R7, and R8 be A2, and the ratio of its input voltage to the output voltage of the amplifier circuit where Q2 is located is p2. Then, ignoring the influence of R11, R12 and the coupling network, the total loop gain A = A1×p1×A2×p2. In order to make the oscillator perform attenuated oscillation when there is no square wave input, A should be very close to but slightly less than 1.

[0049] When there is an injection of a signal from L4, T1, C6, and D3, if the injected signal is significantly different from the resonant frequency of the oscillator, it will not have a significant impact on the attenuated oscillation in the loop. When the frequency of the injected signal is very close to the resonant frequency of the loop, and the phase is the same as the positive feedback signal in the loop, the two signals will be superimposed, so that the total loop gain exceeds 1, and the loop will be able to maintain sinusoidal oscillation. At this time, the oscillation frequency of the loop is pulled by the input signal.

[0050] In this way, the signal with a large difference from the loop resonance frequency is attenuated, while the signal close to the loop resonance frequency can be greatly enhanced, and a pure, low-harmonic sinusoidal signal is obtained.

[0051] The resonant frequency of the LC oscillation circuit can be adjusted by the PWM signal at the "coarse frequency adjustment" input. Since the adjustment range of the varactor diode is extremely small, an analog switch is usually used in the actual circuit. The amplitude of the sinusoidal signal output by the oscillator can be adjusted by the PWM signal input to the "amplitude adjustment" port. This can be understood as the average value of the PWM signal input to the "amplitude adjustment" port, and the square wave switching signal input to the "frequency synchronization" input, are multiplied at Q3 and R13. Since one of the multiplication factors is the switching signal, there is no need to use a more expensive analog multiplier integrated circuit.

[0052] The sine signal output by the LC oscillation circuit is sent to the precision rectifier circuit composed of Q4, R21, Q5, R22, D4, D5, and C17 for detection, and finally the amplitude of the sine signal is output at the "amplitude output" port. The microcontroller can use an algorithm to adjust the PWM signal of the "amplitude adjustment" port to stabilize the amplitude of the sine signal and make the circuit work in the best state.

[0053] The sinusoidal signal output by the LC oscillation circuit is sent to U1 at the same time, multiplied by the external input signal, and then filtered and integrated by the filter circuit composed of U2 and its peripheral components, and the average value of the product of the two signals is output at the "signal output" port. When the two signal frequencies are different, the average value is 0; when the two signal frequencies are the same, the average value is related to the phase difference between the two signals. When the two signals are in phase, the average value is the largest; when the phases are opposite, the average value is the smallest.

[0054] The circuit can be placed as Figure 5 The circuit configuration shown is used. Figure 5 The two square waves in the circuit have a phase difference of exactly 90 degrees and are sent to two identical sine wave phase-locked loops. In this way, the phase difference of the sine waves output by the two sine wave phase-locked loops is 90 degrees. When the external input signal is synchronized or opposite to the phase of one of the sine waves, the phase difference with the other sine wave is 90 degrees, and the average value is 0. In this way, the component of the external input signal at this frequency can be decomposed into sine component and cosine component. This is exactly what the spectrum analysis function needs.

[0055] (1) When this sine wave phase-locked loop is applied to the trigger circuit

[0056] You can take Figure 3The structure shown in the figure. In the figure, while the external input signal is sampled in the high-speed ADC, it will be filtered and then enter the phase detector of the sine wave phase-locked loop as a reference signal, so that the sine wave phase-locked loop outputs a sine wave that is locked to the fundamental wave or specific harmonic of the input signal. This output signal can be used for the trigger function. Since the capture range of the sine wave phase-locked loop can be roughly adjusted, the algorithm can be used in the microcontroller to obtain the frequency range of its fundamental wave or specific harmonic, and control the sine wave phase-locked loop used for the trigger function to work directly in this frequency band to achieve fast triggering.

[0057] At the same time, the microcontroller can adjust the trigger phase by adjusting the working state of the proportional integral circuit of the phase loop of the sine wave phase-locked loop. The microcontroller can also adjust the output amplitude of the sine wave phase-locked loop through the sampling result of the low-speed ADC to obtain the best trigger effect. Figure 4 A reference structure for embedded programs in microcontrollers.

[0058] (2) When this sine wave phase-locked loop is applied to a spectrum analysis circuit

[0059] You can use Figure 5 The structure shown in the figure. The waveform of the high bit of the counter and the waveform obtained by the high and low bit XOR operation are exactly 90 degrees out of phase. The two square waves are input into two sine wave phase-locked loops used for spectrum analysis as reference signals, and low harmonic sine wave signals that are phase-locked can be obtained. The two sine wave signals also differ in phase by 90 degrees. On the one hand, these two output signals enter the low-speed ADC and are collected for amplitude; on the other hand, these two sine signals are multiplied with the external input signal, then integrated (i.e., the filtering link in the figure) to obtain the average value, and finally sampled by the low-speed ADC. By comparing the multiplied signal with the original sine signal, the size of the sine component and cosine component of the external input signal at this frequency can be obtained. When the square wave generated by the counter of the microcontroller scans within a frequency range, the spectrum of the external input signal is obtained. The program that scans the frequency of the square wave can simultaneously change the position where the value collected by the low-speed ADC is written in the RAM, realize the digital storage of the spectrum, and facilitate data exchange with the host computer.

[0060] The microcontroller can also adjust the output amplitude of the sine wave phase-locked loop through the PWM signal according to the amplitude of the two sinusoidal signals to obtain the best working effect. Figure 6 A reference structure for embedded programs in microcontrollers.

[0061] In summary, the present invention has at least the following advantages and beneficial effects compared to the prior art:

[0062] The signal processing logic of the existing virtual oscilloscope is usually located in the controller, so a relatively expensive FPGA or a microprocessor with better performance is required. The present invention designs part of the signal processing logic between the front-end amplifier and the ADC of the virtual oscilloscope, and part of it is implemented by analog circuits. These analog devices are not expensive, and the digital logic part only needs a relatively cheap microcontroller and a host computer interface chip, which reduces the cost of the virtual oscilloscope. At the same time, these analog circuits can be partially shared, the number of devices is small, and the use of patch technology will not increase the size of the virtual oscilloscope. This design also provides convenience for learners and amateurs to modify the circuit and customize the functions.

[0063] In addition, since the analog circuit structures of the trigger and spectrum analysis functions are similar, the present invention also adds a hardware spectrum analysis function to the virtual oscilloscope, thereby expanding its application scenarios.

[0064] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0065] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable ordinary technicians in the field to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made based on the essence of the content of the present invention should be included in the protection scope of the present invention.

Claims

1. A sine wave phase-locked loop circuit realized by frequency pulling effect, characterized in that: It includes an oscillator, a phase loop, an amplitude loop, an analog multiplier and a coupling network; the phase loop includes a phase detector, a first proportional integration circuit and a voltage-controlled oscillator, and the amplitude loop includes a detection circuit and a second proportional integration circuit; The sine wave generated by the oscillator is input into the phase loop and the amplitude loop respectively; In the phase loop, the phase detector compares the phase information of the sine wave with the reference signal, and inputs the comparison result into the first proportional integral circuit for calculation, and the calculation output of the first proportional integral circuit is used to fine-tune the frequency of the voltage-controlled oscillator; In the amplitude loop, the detection circuit compares the amplitude information of the sine wave with the preset PWM signal, and inputs the comparison result into the second proportional integration circuit; The frequency-adjustable waveform generated by the voltage-controlled oscillator and the output of the second proportional-integral circuit are multiplied by an analog multiplier to obtain a waveform with regulated frequency and amplitude. The waveform is coupled into the oscillator through a coupling network to pull the frequency of the oscillator.

2. A sine wave phase-locked loop circuit using frequency pulling effect according to claim 1, characterized in that: The oscillator is an RC oscillator or an LC oscillator.

3. The sine wave phase-locked loop circuit realized by utilizing the frequency pulling effect according to claim 1, characterized in that: The detection circuit is replaced by a rectification circuit.

4. The sine wave phase-locked loop circuit realized by utilizing the frequency pulling effect according to claim 1, characterized in that: The sinusoidal phase-locked loop circuit further includes a pre-filter connected between the analog multiplier and the coupling network.

5. The sine wave phase-locked loop circuit realized by utilizing the frequency pulling effect according to claim 1, characterized in that: The sinusoidal signal output by the sinusoidal phase-locked loop circuit is multiplied by the external input signal and filtered to obtain the frequency component of the external input signal.

6. The sine wave phase-locked loop circuit realized by utilizing the frequency pulling effect according to claim 1, characterized in that: The capture range of the sinusoidal phase-locked loop circuit can be controlled to be roughly adjusted to quickly lock with the fundamental wave or specific subharmonic of the external input signal to obtain a trigger signal synchronized with the fundamental wave or specific subharmonic of the external input signal.

7. The sine wave phase-locked loop circuit realized by utilizing the frequency pulling effect according to claim 1, characterized in that: The reference signal is a reference square wave outputted by the microcontroller; the preset PWM signal is a PWM signal outputted by the microcontroller; A control point is added to the frequency selection network of the oscillator, and the values ​​of the nonlinear resistor, capacitor and inductor are changed by outputting a PWM signal through a microcontroller, so as to roughly adjust the resonant frequency of the oscillator to achieve coarse frequency adjustment.

8. A system, characterized in that: It comprises two sinusoidal phase-locked loop circuits as described in any one of claims 1 to 7, wherein the two sinusoidal phase-locked loop circuits output two sinusoidal signals with a phase difference of 90 degrees, which are used to obtain the sinusoidal component and the cosine component of the frequency component of the external input signal.

9. An oscilloscope using a spectrum analysis circuit, characterized in that: It comprises the sinusoidal wave phase-locked loop circuit as described in any one of claims 1 to 7.

10. An oscilloscope using a trigger circuit, characterized in that: It comprises the sinusoidal wave phase-locked loop circuit as described in any one of claims 1 to 7.

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