RU2259570C2 - Method for measuring the nonlinear distortions of random signals and digital meter (versions) - Google Patents

Abstract

FIELD: electric and radio measurements.

SUBSTANCE: the invention is based on the formation of current ratios of instantaneous values of a signal before and after nonlinear transformation. The current ratios of the neighboring readings of a signal before nonlinear transformation and after nonlinear transformation are compared. The comparison results permit to estimate the degree of nonlinear distortions.

EFFECT: ensuring the possibility of reveal of estimation of nonlinear distortions in the process of fulfillment with an amplifier of its functions.

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Description

The invention relates to the field of electro-radio measurements, is intended to assess the presence and degree of non-linear distortion of a random signal at the output of the sound amplifier path and allows using a random signal transmitted along the path under study as a measuring signal.

The prototype of the claimed device is a structure containing a test signal generator, a notch filter, two rms meters and a division unit, the output of which is the information output of the device, the test output of which is the output of the test signal generator, and the test input is the input of the notch filter, the output of which is connected to the input of the first rms meter, the output of which is connected to the first input of the division unit, the second input of which is connected to the output of W cerned RMS meter having an input merged with the input of the notch filter (Meyzda F. Electronic Instrumentation and Measurement methods: Translated from English - M .: Mir, 1990, str.384 Fig 14.14b]....

The principle of operation of the prototype involves the use of a special measuring signal, usually monoharmonic, according to the results of distortion of which they judge the presence and degree of non-linearity of the path. This feature does not allow the use of devices of this type to evaluate non-linear distortions arising in the process of the amplifier performing its regular functions - amplification of a useful signal, which in reality is random. Marked refers to a significant disadvantage of the prototype,

The technical result achieved by using the present invention is to provide the ability to identify and evaluate non-linear distortions in the process of the amplifier performing its useful functions, without interrupting its operation and transferring it to a special measuring mode. In this case, the digital meter allows you to evaluate the nonlinear distortion of both random and deterministic signals.

The technical result is achieved by the fact that the digital nonlinear distortion meter according to the invention comprises two current relationship conditioners, a subtraction unit, an accumulating adder and a delay element, the outputs of the first and second current relationship conditioners are connected respectively to the first and second inputs of the subtraction unit, the output of which is connected to the information input accumulating adder, the output of which is the output of a digital non-linear distortion meter, the first and second test inputs of which are information inputs of the first and second current relationship conditioners, respectively, whose clock inputs are combined and serve as the clock input of the meter, the clock input of the accumulating adder through a delay element, is connected to the clock input of the meter.

In a digital meter, the current relationship generator comprises a division unit, an analog-to-digital converter, two registers and a delay element, the input of the current relationship generator is the information input of the analog-to-digital converter, the output of which is connected to the information input of the first register, the output of which is connected to the combined information input of the second register and the first input of the division unit, the second input of which is connected to the output of the second register, the output of the division unit is the output of the driver relations, the clock input of which is the combined clock inputs of the analog-to-digital converter and the second register, the clock input of the first register is connected to the clock input of the driver through the delay element.

An attenuator can be additionally introduced into the digital meter, the output of which is connected to the information input of the first current relationship former, and the attenuator input is the first test input of the meter.

In addition, the first and second band-pass filters can be added to the digital meter, the outputs of which are connected to the information inputs of the first and second current-conditioners, respectively, and the inputs of the first and second band-filters serve as the first and second test inputs of the meter.

A digital meter may comprise a constant division unit, the input of which is connected to the output of the accumulating adder, and the output of the division unit serves as the output of the meter.

The invention is illustrated graphic material. Figure 1 presents the functional diagram of a digital meter of nonlinear distortion of random signals with a connected test amplifier. Figure 2 shows a functional diagram of a clock unit.

The functional diagram of FIG. 1 contains identical first F1 and second F2 current-conditioners, which include analog-to-digital converters (ADCs) 1-1, 1-2, registers 2-1, 2-2, 3-1, 3-2 , dividing blocks 4-1, 4-2, as well as delay elements 5-1, 5-2, in addition, the functional diagram contains a subtraction unit 6 accumulating an adder 7, a delay element 8, and a test amplifier 9 with a connected load R _L. The information input of the ADC 1-1 is the information input of the driver F1, the output of the ADC 1-1 is connected to the information input of the register 2-1, the output of which is connected to the combined information input of the register 3-1 and the first input of the division unit 4-1, the second input of which is connected with the output of register 3-1, the output of division block 4-1 is the output of the former F1 and connected to the first input of the subtraction block 6, the second input of which is connected to the output of the former F2, the output of which is the output of the division 4-2, the information input of the former F2 information input of the ADC 1-2, the output of which is connected to the information input of the register 2-2, the output of which is connected to the combined information input of the register 3-2 and the first input of the division unit 4-2, the second input of which is connected to the output of the register 3-2, information the input of the driver F1 is the first test input of the meter and is combined with the output of the amplifier 9, with the input of which the information input of the driver F2 is combined, which (the input) is the second test input of the meter, whose clock input CLK is the combined clock the new inputs of the ADC 1-1, 1-2 and registers 3-1, 3-2, the clock inputs of the registers 2-1 and 2-2 are connected to the clock input of the meter through the elements 5-1 and 5-2 of the delay, respectively, and the clock input the accumulating adder 7 is connected to the clock input CLK of the meter through the delay element 8, the output of the accumulating adder 7 is the output of the meter, the input of the accumulating adder 7 is connected to the output of the subtraction unit 6.

The functional diagram of the clock unit contains triggers 10, 11, a clock generator 12, an element 13 and a counter 14, the overflow output of which is connected to the combined zeroing inputs of the triggers 10, 11, the control input CO of the clock unit is the installation input of the trigger 10, the output of which is connected to - D-input of the trigger 11, the output of which is connected to the first input of the And 13 element, the second input of which is combined with the clock input of the trigger 11 and connected to the output of the clock generator 12, the output of And 13 is the clock in Odom CLK unit and is connected to the counting input of the counter 14.

вносимых нелинейных искажений. Цифровой вариант реализации метода предполагает одновременное вычисление отношений видаThe functioning of the meter is based on the method of estimating non-linear distortions, the idea of which is based on the fact that when a random signal passes through non-linear circuits, the current relations of its instantaneous values change. Therefore, if we compare the current ratios of neighboring samples of the signal before and after the non-linear transformation, then by how much the ratios differ, we can judge the degree

introduced nonlinear distortion. The digital implementation of the method involves the simultaneous calculation of relations of the form

where x (t _n ), y (t _n ) are the quantized samples of the signals x (t) and y (t), respectively;

t _n = t ₀ + nΔt (n = 1, 2, ..., N);

t ₀ is the initial moment of time;

Δt is the sampling period of signals x (f), y (f);

and further determination on a given, normalized time interval T ₀ = NΔt of the sum

By the value of S _xy, the presence and degree of introduced nonlinear distortion is judged: with an increase in the level of nonlinear distortion, S _xy will increase. In the ideal case of the absence of nonlinear distortion, S _xy = 0.

A digital meter of nonlinear distortion of random signals (Fig. 1) works as follows. The output y (t) and input x (f) signals of the studied amplifier 9 are supplied to the drivers F1 and F2, respectively, to calculate the current relations of the form (1). The values obtained at the outputs of the formers are sent to the subtraction unit 6, at the output of which we have the ratio difference module

and further, as can be seen from the diagram (Fig. 1), the calculated value enters the accumulating adder 7 to obtain the sum (2).

Given that the formers F1, F2 are identical, we describe the principle of operation of only one of them, for example, F1.

Before starting the calculations, the entire serial logic of the meter is zeroed by applying a pulse to the RST input (zeroing circuits of registers 2-1, 2-2, 3-1, 3-2 are combined with the zeroing input RST of the accumulating adder and are not shown in the diagram). After zeroing, a packet consisting of N clock pulses is fed to the input CLK of the meter to obtain the first sample S _xy . According to the first clock pulse from the indicated package, the ADC 1-1 starts the conversion of the analog signal y (t) into a digital code, and at the same time, the code from the bit outputs of register 2-1 is written to register 3-1. Since the registers are reset to zero in the initial state, a zero code is written to register 3-1 with the first clock pulse. After a time t _pr equal to the conversion time of the ADC 1-1, the code y (t ₁ ) appears on the ADC output, which is entered in register 2-1. Writing to this register takes place under the action of such a pulse delayed in element 5-1, and the delay time is selected slightly larger than t _pr , that is, sufficient to generate a digital code of the current analogue reference at the ADC 1-1 output. As a result, by the end of the first clock interval, two operands will be fed to the inputs of the division block 4-1: the zero code is the dividend and the value code y (t ₁ ) is the divisor. At the output of block 4-1 in the first clock interval, a zero will be obtained, which is subtracted from the same zero in block 6 and zero (already a difference) is fed to the input of the accumulating adder 7. The first clock interval is a kind of transition interval, and the result will be the next clock it may well be nonzero, since the code y (t ₁ ) is entered in register 3-1 from the output of register 2-1, and a new count y (t ₂ ) appears in register 2-1. Thus, with each next clock pulse at the output of the division unit 4-1, the results of dividing y (t _n ) by y (t _{n + 1} ) will appear.

The process of forming relations of the form (1) and subsequent calculations takes place during the normalized time interval That, which is set by the number N clock pulses in the packet supplied to the input CLK. To form a packet of N pulses, a simple circuit (clock block) shown in Fig. 2 can be used. A short control pulse CO starts the clock block and, as a result, the entire meter (of course, if the output of the clock block CLK is connected to the meter input CLK). With the advent of the first clock pulse, the D-flip-flop 11 enters a state of a high logic level and enables the counting of clock pulses by a counter 14, the conversion coefficient P of which is selected so that a pulse after an N-clock pulse appears at the overflow output. After the counter 14 is overflowed, the triggers 10 and 11 are reset to zero and after the last pulse in the N-pulse packet, the clock block returns to the standby mode of the next control pulse CO.

From the above it is clear that if the described clocking unit is used to control the meter (Fig. 2), then one control pulse should be applied to the input of the CO to receive each next count of the result S _xy . Of course, before applying each control pulse, the operation of zeroing both the meter and the clock unit should be performed.

Regarding the implementation features of the presented meter, we note that the operation of separating the difference module in block 6 is quite simple to perform, if the data at the output of the indicated block are presented in direct code, then the selection of the module is reduced to eliminating the sign discharge of the output code of block 6. Given that accumulating adders are constructed If the circuits contain memory nodes on the registers, then to control their operation, you will certainly need either load pulses or clock pulses in synchronous circuits. To clock the accumulating adder 7, the same clock pulses are used as for the operation of the formers F1, F2, but with a time shift by an amount greater (10-20%) of the time that the meter spends to obtain a new value of the modulus of the relationship difference at the output block 6.

The sampling period Δt and, therefore, the period of formation of the current relations of the form (1) should be selected based on the correlation interval of the studied random signals x (t) and y (t); the accuracy of the calculations depends on Δt and, of course, the period Δt should not exceed the correlation interval. Another factor affecting the accuracy of estimating nonlinear distortions is the group delay time in the tested amplifier 9. In low-cascade audio frequency amplifiers, the delay of the output signal is so small that it can be neglected, however, in multi-link amplification and processing paths, the group delay time must be taken into account.

The principle of operation of the meter was considered on the example of testing a non-inverting amplifier 9. In reality, the amplifier can also be inverting. In such cases, one of the signals x (t), y (t) must be inverted before being fed to the meter. In order to reduce the additional introduced nonlinear distortions, it is advisable to invert the signal with a smaller amplitude, i.e., the input signal x (t). It should also be noted that for large amplifiers of the amplifiers under test, the signal at the first test input of the meter (shaper input F1) should certainly be attenuated, and given that the amplifiers of the amplifiers under test may differ, it would be useful for universal wide-range meters to provide an attenuator that attenuates the output signal of the amplifier (signal supplied to the input of the driver F1).

To reduce the influence of non-uniformity of the amplitude-frequency characteristics of real amplifiers on the result of the assessment of non-linear distortions, the signals x (f), y (t) can be fed to the meter inputs through bandpass filters, highlighting that part of the spectrum within which frequency distortions are insignificant.

Not only the sum of S _xy , but also the average value of S _xy / (N-1) can be a form of estimation of nonlinear distortions. In this case, to obtain an averaged indicator, a dividing unit by the value N-1 should be connected to the output of the meter.

Claims (6)

1. A method for evaluating the nonlinear distortion of random signals, characterized in that they form the current relationship of the instantaneous values of the signal before the nonlinear conversion, form the current relations of the instantaneous values of the signal after the nonlinear conversion, compare the current ratios of neighboring samples of the signal before the nonlinear conversion and after the nonlinear conversion, according to the comparison results judge the degree of non-linear distortion. 2. A digital nonlinear distortion meter, characterized in that it contains two current relationship shapers, a subtraction unit, an accumulating adder and a delay element, the outputs of the first and second current relationship shapers are connected respectively to the first and second inputs of the subtraction block, the output of which is connected to the information input accumulating adder, the output of which is the output of a digital non-linear distortion meter, the first and second test inputs of which are the information inputs corresponding to In addition to the first and second formers of the current relations, the clock inputs of which are combined and serve as the clock input of the meter, the clock input of the accumulating adder is connected to the clock input of the meter through a delay element. 3. A digital nonlinear distortion meter, characterized in that it contains two current relationship conditioners, a subtraction unit, an accumulating adder, an attenuator and a delay element, the outputs of the first and second current relationship conditioners are connected respectively to the first and second inputs of the subtraction unit, the output of which is connected to the information input of the accumulating adder, the output of which is the output of a digital nonlinear distortion meter, the output of the attenuator is connected to the information input of the first shaper current relations, and the attenuator input is the first test input of the meter, the second test input of which is the information input of the second current relationship former, the clock inputs of the current relationship former are combined and serve as the clock input of the meter, the clock input of the accumulating adder is connected to the clock input of the meter through a delay element. 4. A digital nonlinear distortion meter, characterized in that it contains two current relationship conditioners, a subtraction unit, an accumulating adder, two band-pass filters and a delay element, the outputs of the first and second current relationship conditioners are connected respectively to the first and second inputs of the subtraction unit, the output of which connected to the information input of the accumulating adder, the output of which is the output of a digital nonlinear distortion meter, the first and second test inputs of which are the inputs of the first first and second bandpass filters whose outputs are connected to data inputs of the first and second shapers current relationship, the clock inputs of which are combined and clock input meter accumulator clock input through a delay element is connected to a clock input of the meter. 5. A digital nonlinear distortion meter, characterized in that it comprises two current relationship conditioners, a subtraction unit, an accumulating adder, a constant division unit and a delay element, the outputs of the first and second current relationship conditioners are connected to the first and second inputs of the subtraction unit, the output of which is connected to the information input of the accumulating adder, the output of which is connected to the division unit, the output of which is the output of a digital nonlinear distortion meter, the first second test inputs which are data inputs of the first and second shapers current relationship, the clock inputs of which are combined and clock input meter accumulator clock input through a delay element is connected to a clock input of the meter. 6. The current relationship generator for use in the digital nonlinear distortion meter according to any one of claims 2-5 comprises a division unit, an analog-to-digital converter, two registers and a delay element, the input of the current relationship generator is the information input of an analog-to-digital converter, the output of which is connected with the information input of the first register, the output of which is connected to the combined information input of the second register and the first input of the division unit, the second input of which is connected to the output of the second register pa, yield dividing block is the output of the current relationship, the clock input of which is combined clock inputs of analog-to-digital converter and a second register, the first register clock input connected to the clock input through a delay element shaper.

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