Sine small-distortion-degree signal measuring method

Abstract

The invention provides a sine small distortion degree signal measuring method, a measuring device comprises a distortion degree measuring instrument and a spectrum analyzer, and the method comprises the following steps: S1, deducing a total distortion formula D of a sine small distortion signal; s2, calibrating the distortion degree measuring instrument, and determining the fundamental wave suppression amount C of the distortion degree measuring instrument; s3, determining a harmonic residual distortion degree Dns; an output signal of the fundamental wave suppressor comprises a residual fundamental wave and each harmonic signal, the signal is monitored by the distortion degree measuring instrument and output to the spectrum analyzer, and the spectrum analyzer visually displays the power intensity of the residual fundamental wave and each harmonic signal; and S4, calculating the distortion degree D of the measured small sine signal. According to the method, the advantages of the fundamental wave suppression method and the spectrum analyzer method are combined, the fundamental wave suppression quantity of the fundamental wave suppression network and the harmonic levels measured by the spectrum analyzer are integrated, the lower limit of sinusoidal signal distortion degree measurement can be reduced to-130 dB, and therefore the problem that small sinusoidal distortion signals cannot be accurately measured is solved.

Description

Technical Field

[0001] The present invention relates to the field of distortion measurement, further to the field of distortion measurement in radio electronics, and in particular to a method for measuring a sinusoidal small-distortion signal. Background Art

[0002] Nonlinear distortion is a crucial parameter in radio measurement and is widely used in audio measurement. Most distortion meters currently available on the market use a fundamental suppression method to measure distortion. This method utilizes a passive network with a fixed-frequency suppression function as a fundamental suppression circuit. When measuring the distortion of a sinusoidal signal, the fundamental component is first suppressed by the fundamental suppression circuit, and the distortion is calculated based on the remaining harmonic components. Some distortion meters also use spectrum analyzers to measure the distortion of sinusoidal signals. These instruments primarily measure the fundamental and harmonic components of the sinusoidal signal, and then calculate the distortion of the measured sinusoidal signal according to the definition of distortion. However, the fundamental suppression method, due to the instrument's fundamental suppression depth and the effects of internally introduced distortion, limits the instrument's measurement range to -80dB. When measuring distortion using spectrum analysis, the lower limit is usually only -90dB due to the distortion and dynamic range limitations of the spectrum analyzer itself. Therefore, neither method is suitable for measuring low-distortion signals (-90dB to -130dB).

[0003] The Chinese paper "Design and Implementation of an Analog Signal Distortion Measurement Device" designed a signal distortion measurement device. This device first transforms the input signal through an op amp and an offset circuit to within the sampling range of the analog-to-digital converter. A fast Fourier transform algorithm is then used to obtain the normalized amplitudes of the fundamental and harmonics. Frequency domain analysis is then used to calculate the distortion of the sampled signal. This method achieves distortion measurement through hardware circuit design and software algorithm design. The Chinese paper "Design of a Signal Distortion Measurement Device" also employed hardware circuit design, designing a THD harmonic distortion measurement device based on an FFT algorithm and AGG automatic gain control circuit. However, neither design was able to accurately measure sinusoidal signals with low distortion. Summary of the Invention

[0004] In order to solve the above problems, the present invention provides a device for measuring a sinusoidal low-distortion signal.

[0005] The specific technical solutions of the present invention are as follows:

[0006] A method for measuring a sinusoidal low-distortion signal, wherein the measuring device includes a distortion meter and a spectrum analyzer, and specifically comprises the following steps:

[0007] S1. Derive the calculation formula of the measured sinusoidal small signal distortion D;

[0008] S2. Calibrate the distortion meter to determine the fundamental wave suppression value C of the distortion meter;

[0009] S3. Determine the harmonic residual distortion D ns When the distortion meter is operating in a distorted state and the fundamental suppressor achieves optimal suppression of the fundamental wave, ignoring the distortion introduced by the distortion meter, the output signal of the fundamental suppressor contains the remaining fundamental wave and each harmonic signal. This signal is output from the distortion meter's monitoring output to the spectrum analyzer, which intuitively displays the power intensity of the remaining fundamental wave and each harmonic signal. In actual measurements, the energy of each harmonic is mainly concentrated in the second and third harmonics, and the remaining harmonic components can be ignored.

[0010] S4. Calculate the distortion D of the measured sinusoidal small signal.

[0011] Preferably, the step S1 comprises the following steps:

[0012] S11. Use the fundamental suppressor of the distortion meter as the fundamental suppression network, and use a spectrum analyzer to measure the harmonic signal after passing through the fundamental suppression network.

[0013] S12, let the fundamental power of the measured sinusoidal signal be P1, and the power of the nth harmonic signal be P n (n=2,3…)dBm, the fundamental power after passing through the fundamental suppression network with a fundamental suppression amount of C is P 1s , the harmonic power is P ns (n=2,3…)dBm, then the nth harmonic distortion of the measured sinusoidal signal is D n for:

[0014]

[0015] S13. Assume that the fundamental wave suppression network only suppresses the fundamental wave, and the harmonic signal can pass through without any influence, that is, P ns =P n , then the above formula can be expressed as:

[0016]

[0017] Right now:

[0018] D n (dB) = D ns +C (1)

[0019] in: It is the residual distortion of the nth harmonic of the measured sinusoidal signal after passing through the fundamental wave suppression network; is the suppression amount of the fundamental wave by the fundamental wave suppressor of the distortion meter; then the distortion degree D of the measured sinusoidal small signal can be expressed as:

[0020]

[0021] in: (Definition of distortion).

[0022] Preferably, step S2 comprises the following steps:

[0023] S21. Put the distortion meter into calibration mode and adjust the calibration potentiometer so that the meter indicates full scale. Then use a spectrum analyzer to measure the fundamental power level of the sinusoidal signal under test to obtain P1dBm.

[0024] S22. Adjust the switch to make the distortion meter work in the distortion state and measure the distortion of the sinusoidal signal under test. When the distortion meter works in the optimal tuning state, that is, when the fundamental wave suppressor of the distortion meter reaches the optimal suppression state for the sinusoidal signal, use the spectrum analyzer to measure the residual fundamental wave power level P1s dBm.

[0025] S23. The fundamental wave suppression amount of the distortion meter is:

[0026] C(dB)=P 1s -P1+C s (3)

[0027] Where C s This is the range where the pointer of the distortion meter is located when it achieves the best suppression state for the fundamental wave.

[0028] Preferably, step S3 comprises the following steps:

[0029] Use a spectrum analyzer to measure the residual fundamental power level P 1s dBm, nth harmonic power level P ns dBm, then the nth residual harmonic distortion D ns It can be expressed as:

[0030] D ns (dB) = P ns -P 1s (4)

[0031] Preferably, step S4 comprises the following steps:

[0032] Substituting equations (3) and (4) into equation (1), we can get the nth harmonic distortion D of the measured sinusoidal signal: n for:

[0033] D n(dB)=D ns +C

[0034] =(P ns -P 1s )+(P 1s -P1+C s )

[0035] =P ns -P1+C s (5)

[0036] It can be seen from formula (5) that when using the fundamental suppression + spectrum analysis method to measure ultra-low distortion, it is only necessary to use a spectrum analyzer to measure the harmonic power P when the distortion meter is working in the distortion state. ns dBm, the fundamental signal power P1 when the distortion meter is working in the calibration state, the range C where the pointer is located when the distortion meter achieves the best suppression state for the fundamental wave s , the nth harmonic distortion D of the measured sinusoidal signal can be obtained n , and then substitute equation (5) into equation (2) to calculate the total distortion D of the measured sinusoidal small distortion signal.

[0037] Preferably, the distortion meter adopts the fundamental wave suppression measurement principle and includes a fundamental wave suppression circuit; the fundamental wave suppression circuit is used to attenuate the fundamental wave component of the sinusoidal signal by several tens of decibels, so that the attenuated sinusoidal signal fully adapts to the harmonic dynamic range of the spectrum analyzer, that is, before the sinusoidal signal enters the spectrum analyzer, a fundamental wave suppression network is added to allow the harmonic signal to pass through without attenuation; the spectrum analyzer is used to test the harmonic level.

[0038] Preferably, the frequency measurement lower limit of the spectrum analyzer is -130dBm.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention develops a sinusoidal small-distortion signal measurement device that combines the fundamental wave suppression method and spectrum analysis method for distortion measurement. This method, combining the advantages of the fundamental wave suppression method and spectrum analysis method, can effectively reduce the lower limit of sinusoidal signal distortion measurement to -130dB, thereby solving the problem of inability to accurately measure sinusoidal small-distortion signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0042] Figure 1 It is a schematic diagram of the method for measuring a small-distortion sinusoidal signal according to the present invention. DETAILED DESCRIPTION

[0043] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0044] It should be noted that the illustrations provided in the following embodiments are merely schematic illustrations of the basic concept of the present invention. Therefore, the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation. In actual implementation, the type, quantity, and proportion of each component may be changed arbitrarily, and the component layout may also be more complex.

[0045] The following is combined with Figure 1 The present invention is described in further detail:

[0046] A method for measuring a sinusoidal low-distortion signal, such as Figure 1 As shown, the measurement device includes a distortion meter and a spectrum analyzer, and specifically includes the following steps:

[0047] S1. Derive the calculation formula of the measured sinusoidal small signal distortion D;

[0048] S2. Calibrate the distortion meter to determine the fundamental wave suppression value C of the distortion meter;

[0049] S3. Determine the harmonic residual distortion D ns When the distortion meter is operating in a distorted state and the fundamental suppressor achieves optimal suppression of the fundamental wave, ignoring the distortion introduced by the distortion meter, the output signal of the fundamental suppressor contains the remaining fundamental wave and each harmonic signal. This signal is output from the distortion meter's monitoring output to the spectrum analyzer, which intuitively displays the power intensity of the remaining fundamental wave and each harmonic signal. In actual measurements, the energy of each harmonic is mainly concentrated in the second and third harmonics, and the remaining harmonic components can be ignored.

[0050] S4. Calculate the distortion D of the measured sinusoidal small signal.

[0051] Preferably, the step S1 comprises the following steps:

[0052] S11. Use the fundamental suppressor of the distortion meter as the fundamental suppression network, and use a spectrum analyzer to measure the harmonic signal after passing through the fundamental suppression network.

[0053] S12, suppose the fundamental power of the measured sinusoidal signal is P1 dBm, and the power of the nth harmonic signal is P n

[0054] (n=2,3…)dBm, the fundamental power after passing through the fundamental suppression network with a fundamental suppression amount of C is P 1s , the harmonic power is P ns (n=2,3…)dBm, then the nth harmonic distortion of the measured sinusoidal signal is D n for:

[0055]

[0056] S13. Assume that the fundamental wave suppression network only suppresses the fundamental wave, and the harmonic signal can pass through without any influence, that is, P ns =P n , then the above formula can be expressed as:

[0057]

[0058] Right now:

[0059] D n (dB)=D ns +C (1)

[0060] in: It is the residual distortion of the nth harmonic of the measured sinusoidal signal after passing through the fundamental wave suppression network; is the suppression amount of the fundamental wave by the fundamental wave suppressor of the distortion meter; then the distortion degree D of the measured sinusoidal small signal can be expressed as:

[0061]

[0062] in: (Definition of distortion).

[0063] The step S2 comprises the following steps:

[0064] S21. Put the distortion meter into calibration mode and adjust the calibration potentiometer so that the meter indicates full scale. Then use a spectrum analyzer to measure the fundamental power level of the sinusoidal signal under test to obtain P1dBm.

[0065] S22. Adjust the switch to make the distortion meter work in the distortion state and measure the distortion of the sinusoidal signal under test. When the distortion meter works in the optimal tuning state, that is, when the fundamental wave suppressor of the distortion meter reaches the optimal suppression state for the sinusoidal signal, use the spectrum analyzer to measure the residual fundamental wave power level P1s dBm.

[0066] S23. The fundamental wave suppression amount of the distortion meter is:

[0067] C(dB)=P 1s -P1+C s (3)

[0068] Where C s This is the range where the pointer of the distortion meter is located when it achieves the best suppression state for the fundamental wave.

[0069] The step S3 comprises the following steps:

[0070] Use a spectrum analyzer to measure the residual fundamental power level P 1s dBm, nth harmonic power level P ns dBm, then the nth residual harmonic distortion D ns It can be expressed as:

[0071] D ns (dB) = P ns -P 1s (4)

[0072] The step S4 comprises the following steps:

[0073] Substituting equations (3) and (4) into equation (1), we can get the nth harmonic distortion D of the measured sinusoidal signal: n for:

[0074] D n (dB)=D ns +C

[0075] =(P ns -P 1s )+(P 1s -P1+C s )

[0076] =P ns -P1+C s (5)

[0077] It can be seen from formula (5) that when using the fundamental suppression + spectrum analysis method to measure ultra-low distortion, it is only necessary to use a spectrum analyzer to measure the harmonic power P when the distortion meter is working in the distortion state. ns dBm, the fundamental signal power P1 when the distortion meter is working in the calibration state, the range C where the pointer is located when the distortion meter achieves the best suppression state for the fundamental wave s , the nth harmonic distortion D of the measured sinusoidal signal can be obtained n , and then substitute formula (5) into formula (2) to calculate the distortion D of the measured sinusoidal small signal.

[0078] The distortion meter uses the fundamental wave suppression measurement principle and includes a fundamental wave suppression circuit. The fundamental wave suppression circuit is used to attenuate the fundamental wave component of the sinusoidal signal by several tens of decibels, so that the attenuated sinusoidal signal fully adapts to the harmonic dynamic range of the spectrum analyzer. That is, before the sinusoidal signal enters the spectrum analyzer, a fundamental wave suppression network is added, allowing the harmonic signal to pass through without attenuation. The spectrum analyzer is used to test the harmonic level.

[0079] The frequency measurement lower limit of the spectrum analyzer is -130dBm.

[0080] The specific principle is as follows Figure 1 As shown, turn the switch to the calibration state, the measured signal is adjusted through the input circuit and directly sent to the detection output, and then transmitted to the meter and spectrum analyzer part respectively through the detection output; adjust the calibration potentiometer of the distortion meter so that the meter head of the distortion meter indicates full scale. At this time, the fundamental power level of the measured sinusoidal signal measured by the spectrum analyzer is P1 dBm; turn the switch to the distortion state, the measured signal is adjusted through the input circuit and then suppressed by the fundamental suppressor. The remaining harmonic signals are transmitted to the spectrum analyzer part, and the spectrum analyzer part measurement data P is obtained. ns dBm, combined with data P ns D is calculated using dBm, P1 dBm and derived formulas (1) to (5).

[0081] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may use the above-disclosed contents to make possible changes and modifications to the technical solutions of the present invention without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the contents of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. A method for measuring a sinusoidal low-distortion signal, wherein the measuring device comprises a distortion meter and a spectrum analyzer, and wherein: The specific steps are as follows: S1. Derive the calculation formula of the measured sinusoidal small signal distortion D; S2. Calibrate the distortion meter to determine the fundamental wave suppression value C of the distortion meter; S3. Determine the harmonic residual distortion D ns Ignoring the distortion introduced by the distortion meter, the output signal of the fundamental suppressor contains the remaining fundamental wave and each harmonic signal. This signal is output by the distortion meter to the spectrum analyzer, which intuitively displays the power intensity of the remaining fundamental wave and each harmonic signal. In actual measurements, the energy of each harmonic is mainly concentrated in the second and third harmonics, and the other harmonic components can be ignored. S4. Calculate the distortion D of the measured sinusoidal small signal.

2. The method for measuring a sinusoidal low-distortion signal according to claim 1, wherein: The step S1 comprises the following steps: S11. Use the fundamental wave suppressor of the distortion meter as the fundamental wave suppression network, and use a spectrum analyzer to measure the harmonic signal after passing through the fundamental wave suppression network. S12, let the fundamental power of the measured sinusoidal signal be P1, and the power of the nth harmonic signal be P n (n=2, 3...), the fundamental power after passing through the fundamental suppression network with a fundamental suppression amount of C is P 1s dBm, harmonic power is P ns (n=2,3…), then the nth harmonic distortion of the measured sinusoidal signal is D n for: S13. Assume that the fundamental wave suppression network only suppresses the fundamental wave, and the harmonic signal can pass through without any influence, that is, P ns =P n , then the above formula can be expressed as: Right now: D n (dB)=D ns +C (1) in: It is the residual distortion of the nth harmonic of the measured sinusoidal signal after passing through the fundamental wave suppression network; is the suppression amount of the fundamental wave by the fundamental wave suppressor of the distortion meter; then the distortion degree D of the measured sinusoidal small signal can be expressed as: in:

3. The method for measuring a sinusoidal low-distortion signal according to claim 1, wherein: The step S2 comprises the following steps: S21. Place the distortion meter in the calibration state and adjust the calibration potentiometer so that the meter indicates full scale. Then, use a spectrum analyzer to measure the fundamental power level of the sinusoidal signal under test as P1. S22. Adjust the switch to make the distortion meter work in the distortion state and measure the distortion of the measured sinusoidal signal. When the distortion meter works in the best tuning state, that is, when the fundamental wave suppressor of the distortion meter reaches the best suppression state for the sinusoidal signal, use the spectrum analyzer to measure the residual fundamental wave power level P at this time. 1s ; S23. The fundamental wave suppression amount of the distortion meter is: C(dB)=P 1s -P1+C s (3) Where C s This is the range where the pointer of the distortion meter is located when it achieves the best suppression state for the fundamental wave.

4. The method for measuring a sinusoidal low-distortion signal according to claim 1, wherein: The step S3 comprises the following steps: Use a spectrum analyzer to measure the residual fundamental power level P 1s , nth harmonic power level P ns dBm, then the nth residual harmonic distortion D ns It can be expressed as: D ns (dB)=P ns -P 1s (4)。 5. The method for measuring a sinusoidal low-distortion signal according to claim 1, wherein: The step S4 comprises the following steps: Substituting equations (3) and (4) into equation (1), we can get the nth harmonic distortion D of the measured sinusoidal signal: n for: D n (dB)=D ns +C =(P ns -P 1s )+(P 1s -P1+C s ) =P ns -P1+C s (5) Substituting equation (5) into equation (2), the distortion D of the measured sinusoidal small signal can be calculated.

6. The method for measuring a sinusoidal low-distortion signal according to claim 1, wherein: The distortion meter adopts the fundamental wave suppression measurement principle and includes a fundamental wave suppression circuit; The fundamental wave suppression circuit is used to attenuate the fundamental wave component of the sinusoidal signal by several tens of decibels, so that the attenuated sinusoidal signal fully adapts to the harmonic dynamic range of the spectrum analyzer. That is, before the sinusoidal signal enters the spectrum analyzer, a fundamental wave suppression network is added to allow the harmonic signal to pass through without attenuation. The spectrum analyzer is used to test harmonic levels.

7. The method for measuring a sinusoidal low-distortion signal according to claim 1, wherein: The frequency measurement lower limit of the spectrum analyzer is -130dBm.

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