RU214156U1 - Device for measuring non-linear distortions of an electrical signal with increased noise immunity - Google Patents

Abstract

The utility model relates to the field of instrumentation and is designed to identify and evaluate various types of non-linear distortions of an electrical signal introduced by audio equipment, in particular, preamplifiers and power amplifiers. At the input of the differentiation block, a forcing-inertial link is introduced, consisting of the fifth resistor connected in parallel and the fourth capacitor, which is tunable simultaneously with the other capacitors of the block. The utility model improves the noise immunity of the device. The technical result consists in narrowing the frequency range of the relative noise amplification in the differentiation block. 1 ill., 1 tab.

Description

Technical field

The utility model relates to the field of instrumentation and is designed to identify and evaluate various types of non-linear signal distortions introduced by audio equipment, in particular, preamplifiers and power amplifiers for audio signals.

The purpose of the utility model is to improve the noise immunity of the device.

This is achieved by narrowing the frequency range of the relative amplification of interference in the differentiation block, which is ensured by introducing an additional link into the differentiation block containing three delay links, for which a forcing-inertial link is introduced at the input of the differentiation block, consisting of a fifth resistor and a fourth capacitor connected in parallel, tunable simultaneously with other block capacitors.

Description of analogues

A device for measuring non-linear distortion of an electrical signal [1].

The device contains a generator of harmonic oscillations connected in series, a measurement object, a signal level equalization unit, consisting of an attenuator and an adjustable measuring amplifier connected in series, the attenuator input being the input of the signal level equalization unit, and the output of the adjustable measuring amplifier being its output, a differentiation unit containing two delay link, including simultaneously tunable capacitors, a control and measuring unit consisting of an oscilloscope and a measuring unit that are connected to the input of the control and measuring unit, as well as identical first and second display units, consisting of a comparison circuit, the first input of which is the input of the indication block, the reference signal generator connected to the second input of the comparison circuit, the indicator connected to the output of the comparison circuit, the input of the first indication block is connected to the output of the signal level equalization block, and the input of the second th indication block is connected to the output of the differentiation block, input and output terminals for connecting the measurement object.

The reasons hindering the achievement of the required technical result include low measurement accuracy due to methodological errors.

Description of the prototype

The closest solution for the same purpose in terms of a set of features is a device for measuring nonlinear distortions of an electrical signal with increased noise immunity [2].

The device contains input and output terminals for connecting a measurement object, a harmonic generator, the output of which is connected to the input terminal, a signal level equalization unit is connected to the output terminal, consisting of an attenuator and an adjustable measuring amplifier connected in series, and the attenuator input is the input of the signal level equalization unit , and the output of the adjustable measuring amplifier is its output, a differentiation block containing three delay links, including the first resistor forming the input of the differentiation block and connected to the input of the first inverting amplifier, the second resistor connected in parallel and the first capacitor connected between the input and output of the first inverting amplifier and forming a feedback circuit, a second capacitor and a third resistor connected in series, connected between the output of the first inverting amplifier and the input of the second inverting amplifier, and also i.e. the fourth resistor and the third capacitor connected in parallel to each other, connected between the input and output of the second inverting amplifier and forming a feedback circuit, while the capacitors of the differentiation unit are tuned simultaneously, a control and measuring unit is connected to the output of the second inverting amplifier, which forms the output of the differentiation unit, consisting of an oscilloscope and a measuring unit, which are connected with their inputs to the input of the control and measuring unit, in addition, the device includes identical first and second indication units, consisting of a comparison circuit, the first input of which is the input of the indication unit, a reference signal generator connected to the second input of the comparison circuit, an indicator connected to the output of the comparison circuit, wherein the input of the first indication block is connected to the output of the signal level equalization block, and the input of the second indication block is connected to the output of the differentiation block. Criticism of the prototype

The reasons hindering the achievement of the desired technical result when using the known device, adopted as a prototype, include the fact that the device has a relatively low noise immunity due to a wide frequency range of the relative noise gain in the differentiated signal, which reduces the measurement accuracy of the non-linear distortions of the electrical signal.

The essence of the utility model

The problem to be solved by the utility model is to increase the noise immunity of the device.

This problem is solved by achieving a technical result in the implementation of the useful model, which is achieved by narrowing the frequency range of the relative amplification of interference in the differentiation block, which is ensured by introducing an additional link into the differentiation block containing three delay links.

The specified technical result in the implementation of the utility model is achieved by the fact that at the input of the differentiation block, a forcing-inertial link is introduced, consisting of a fifth resistor connected in parallel and a fourth capacitor, which is tunable simultaneously with other capacitors of the block.

The analysis of the level of technology carried out by the applicant, including a search on patent and scientific and technical sources of information, made it possible to establish that the applicant did not find an analogue characterized by features identical to all the essential features of the claimed utility model, but the definition of a prototype from among the identified analogues as the closest in totality features, made it possible to determine the set of features essential in relation to the technical result in the declared object, set forth in the formula of the utility model.

Therefore, the claimed utility model meets the requirement of "novelty".

List of drawing figures

The figure shows a block diagram of a device that implements the proposed utility model, where 1 is a generator of harmonic oscillations; 2 - input terminal; 3 - measurement object; 4 - output terminal; 5 - signal level equalization block; 6 - attenuator; 7 - adjustable measuring amplifier; 8 - differentiation block; 9 - the first resistor R1; 10 - second resistor R2; 11 - variable first capacitor C1; 12 - the first inverting amplifier; 13 - variable second capacitor C2; 14 - third resistor R3; 15 - fourth resistor R4; 16 - variable third capacitor C3; 17 - second inverting amplifier; 18 - control and measuring unit; 19 - oscilloscope; 20 - measuring block; 21 - the first display unit, 22 - the first comparison circuit; 23 - the first generator of the reference signal; 24 - the first indicator; 25 - second display unit; 26 - second comparison circuit; 27 - the second generator of the reference signal; 28 - second indicator; 29 - fifth resistor R5; 30 - variable fourth capacitor C4. The capacitors of the differentiation block are rebuilt simultaneously.

Information confirming the possibility of implementing the utility model

Information confirming the possibility of implementing the utility model with obtaining the specified technical result is as follows.

The device includes series-connected generator 1 of harmonic oscillations, input terminal 2 and output terminal 4 for connecting the measurement object 3, a signal level equalization unit 5 is connected to the output terminal 4, consisting of a series-connected attenuator 6 and an adjustable measuring amplifier 7, and the attenuator input 6 is the input of the signal level equalization block 5, and the output of the adjustable measuring amplifier 7 is its output, to which the differentiation block 8 is connected, containing the first resistor 9, which forms the input of the differentiation block 8 and connected to the input of the first inverting amplifier 12, the second one connected in parallel resistor 10 and the first capacitor 11 connected between the input and output of the first inverting amplifier 12 and forming a feedback circuit, the second capacitor 13 and the third resistor 14 connected in series connected between the output of the first inverting amplifier 12 and the input of the second inverter 17, as well as the fourth resistor 15 and the third capacitor 16 connected in parallel to each other, connected between the input and output of the second inverting amplifier 17 and forming a feedback circuit, while the capacitors of the differentiation unit are tuned simultaneously, to the output of the second inverting amplifier 17, which forms the output differentiation block 8, connected to the control and measuring unit 18, consisting of an oscilloscope 19 and measuring unit 20, which are connected to the input of the control and measuring unit 18, in addition to the output of block 5 for equalizing signal levels, the first display unit 21 is connected, consisting of the first circuit 22 comparison, one of the inputs of which is the input of the indication block 21, the first reference signal generator 23 connected to another input of the first comparison circuit 22, the first indicator 24 connected to the output of the first comparison circuit 22, the second indication block 25 is connected to the output of the differentiation block 8, consisting of second circuit 26 comparison, one of the inputs of which is the input of the second block 25 display, the second generator 27 of the reference signal connected to another input of the second circuit 25 comparison, the second indicator 28 connected to the output of the second circuit 25 comparison.

Block 8 differentiation of the prototype device is a direct active differentiator with three links of delay, having one zero and three poles in the transfer function

where T=R ₄ C ₂ R ₂ /R ₁ ; T ₁ =R ₃ C ₂ ; T ₂ =R ₄ C ₃ and T ₃ =R ₂ C ₁ with the voltage gain of the first and second inverting amplifiers K1 and K2>>1.

To reduce the zone of relative amplification of the noise of the prototype device time constants delay are set equal to each other: T ₁ =T ₂ =T ₃ . In this case, the frequency response and phase response of the block 8 differentiation have the form

ϕ(ω)=(π/2)-3arctg ωT ₁ =(π/2)-Δϕ(ω),

where γ(ω)≈1.5ω ² T ₁ ² (when ωТ ₁ <0.2); Δϕ(ω)=3arctg ωT ₁ .

The presence in the studied signal of interference and noise of active devices included in the differentiation block 8 circuit negatively affects the measurement results, causing measurement error, which is inherent in the very method of differentiation carried out using technical means. It is possible to increase the noise immunity of the differentiator, and hence the entire device, by optimizing the structure and parameters of the differentiator circuit.

In particular, this problem can be solved by introducing at the input of the differentiation block 8 of the prototype device an additional forcing-inertial link having a forcing time constant T _f , and consisting of parallel-connected fifth resistor R5 (29) and a variable fourth capacitor C4 (30), tunable simultaneously with other capacitors block 8 differentiation. Approximate differentiation will be carried out by subtracting the lagging signal from the signal leading in phase to the signal under study. In this case, the time shift or phase difference between the subtracted signals can be relatively large (within tenths of the period of the signal under study), which causes a decrease in the relative influence of noise on the accuracy characteristics of the differentiation block 8, and therefore to increase the noise immunity of its operation.

The transfer function of the proposed device will include one zero, the boost constant T _f and the delay time constants T ₁ -T ₄ :

where T=R ₄ C ₂ ; T _F =R ₅ C ₄ ; T ₁ =R ₃ C ₃ ; T ₂ =R ₄ C ₃ ; T ₃ =R ₅ R ₁ C ₁ /(R ₅ +R ₁ ); T ₄ =R ₂ C ₁ ; R ₂ \u003d R ₅ + R ₁ (at K1 and K2>> 1).

To improve the noise immunity should be set to T ₁ =T ₂ and T ₃ =T ₄ . Taking into account what the frequency response and phase response of the block 8 differentiation will have the form

ϕ(ω)=(π/2)+arctg ωТ _f -2arctg ωT ₁ -2arctg ωТ ₃ =(π/2)+Δϕ(ω),

where γ(ω)≈(ω ² T _f ² /2)-ω ² T ₁ ² -ω ² T ₃ ² (at ωT _f <0.4; ωT ₁ , ωT ₃ <0.2); Δϕ(ω)=arctg ωТ _f -2arctg ωT ₁ -2arctg ωТ ₃ .

The errors γ(ω) and Δϕ(ω) include components with different signs (“+” and “-”), therefore, by choosing the appropriate values of the time constants T _f , T ₁ and T ₃ , you can get both positive and negative the values of errors γ(ω) and Δϕ(ω) or to ensure the minimum values of these errors in a wide frequency range.

The greatest gain in accuracy and noise immunity is provided when the following inequalities are fulfilled:

T _f > (T ₁ +T ₃ ) - to minimize the amplitude error γ(ω),

T _f > 2(T ₁ +T ₃ ) - to minimize the phase error Δϕ(ω).

In this case, the differentiation of the signal at the lower frequencies of the operating range will be carried out with positive errors γ(ω) or Δϕ(ω), and at the upper frequencies - with their negative values. Specific values of the time constants T _f , T ₁ and T ₃ must be calculated according to the form of the frequency response or phase response so that the amplitude or phase errors do not exceed the modulus of the allowable limits in the entire operating frequency range of the device.

от величины погрешности γ(ω_в) дифференцирования на верхней частоте рабочего диапазона дифференцирования ω_в для устройства-прототипа и заявляемого устройства. Зависимости получены при наиболее оптимальных соотношениях между значениями постоянными времени: Т_ф=2Т₃ и T₁<Т₃.The table summarizes the results of calculations of the dependences of the width of the frequency range of the relative gain of interference

on the value of the error γ(ω _in ) differentiation at the upper frequency of the operating range of differentiation ω _in for the prototype device and the proposed device. The dependencies were obtained with the most optimal ratios between the values of the time constants: T _f =2T ₃ and T ₁ <T ₃ .

сужается в 19 раз. При увеличении погрешности выигрыш в помехоустойчивости снижается, однако даже при γ(ω_в)=1% обеспечивается ослабление помех в 7.5 раз.The data in the table show that the introduction of an additional forcing-inertial link in the circuit block 8 differentiation allows you to drastically reduce the bandwidth of the relative amplification of noise than to increase the noise immunity of the device. In particular, at γ(ω _in )=0.05% the frequency range

shrinks 19 times. With an increase in the error, the gain in noise immunity decreases, however, even at γ(ω _in )=1%, interference is attenuated by a factor of 7.5.

From the foregoing, it follows that the introduction of an additional forcing-inertial link with a capacitor into the differentiation block 8, which is simultaneously tunable together with other capacitors of the block, provides an increase in the noise immunity of the differentiation block, and hence the entire device, which is ensured by narrowing the frequency range of the relative noise amplification in the studied signal.

Thus, the above information indicates that the following conditions are met when using the claimed utility model:

- a device that embodies the claimed utility model in its implementation, is intended for use in instrumentation to identify and evaluate various types of non-linear distortions introduced by audio equipment, in particular preamplifiers and power amplifiers.

- for the claimed model in the form as it is characterized in the formula of the utility model, the possibility of its implementation using the means described above in the application or known before the priority date is confirmed;

- a device that embodies the claimed model in its implementation is capable of achieving the specified technical result.

Therefore, the claimed invention meets the requirement of "industrial applicability" under the current legislation. Literature

1. SU 1318926 A1, G01R 23/20, publ. 06/23/1987, bul. No. 23.

2. Patent for invention 2477492 (RU 2 477 492 C2). Russian Federation, IPC G01R 23/20 (2006.01). A device for measuring non-linear distortions of an electrical signal with increased noise immunity [Text] / Tikhonova L.S.; applicant and patent holder St. Petersburg State University of Cinema and Television. - Application No. 2010126710/28, 06/29/2010. Published: 03/10/2013 Bull. No. 7 (prototype).

Claims (1)

A device for measuring non-linear distortions of an electrical signal with increased noise immunity, containing input and output terminals for connecting the measurement object, a harmonic oscillation generator, the output of which is connected to the input terminal, a signal level equalization unit is connected to the output terminal, consisting of an attenuator connected in series and an adjustable measuring amplifier , wherein the input of the attenuator is the input of the signal level equalization block, and the output of the adjustable measuring amplifier is its output, the differentiation block, containing three delay links, including the first resistor, which forms the input of the differentiation block and is connected to the input of the first inverting amplifier, connected in parallel a second resistor and a first capacitor connected between the input and output of the first inverting amplifier and forming a feedback circuit, a second capacitor and a third resistor connected in series, connected waiting for the output of the first inverting amplifier and the input of the second inverting amplifier, as well as the fourth resistor and the third capacitor connected in parallel to each other, connected between the input and output of the second inverting amplifier and forming a feedback circuit, while the capacitors of the differentiation unit are tuned simultaneously to the output of the second inverting amplifier , forming the output of the differentiation unit, a control and measuring unit is connected, consisting of an oscilloscope and a measuring unit, which are connected to the input of the control and measuring unit, in addition, the device includes identical first and second display units, consisting of a comparison circuit, the first input of which is the input of the indication block, the reference signal generator connected to the second input of the comparison circuit, the indicator connected to the output of the comparison circuit, and the input of the first indication block is connected to the output of the signal level equalization block, and the input of the second block dictation is connected to the output of the differentiation block, characterized in that at the input of the differentiation block, a forcing-inertial link is introduced, consisting of the fifth resistor connected in parallel and the fourth capacitor, which is tunable simultaneously with the other capacitors of the block.

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