Meter frequency distortion (options)

 

The meter is designed to determine the level of frequency distortion of a two-port, for example, amplification of audio signals. Using the test signal generator and spectrum analyzer to form the signal, the instantaneous value of which is determined by the value of the normalized amplitude-frequency characteristics of the quadrupole. Then the received signal is fed to the input of the subtraction unit. To the second input of the subtraction is supplied to a fixed voltage. The output of the subtraction unit is connected to the input of the unit selection module. The output of the block selection module is connected to the input of the integrator. Quantitative assessment criterion frequency distortion is the square of the frequency distortion resulting from the integration. In the second embodiment, the subtraction unit replaced by the unit taking the logarithm. The meter allows you to enhance the usefulness of the evaluation of the frequency distortion of a quadrupole in the original signal. 2 N. p. F.-ly, 3 ill.

The invention relates to the field of radio, and is intended for integral assessment of the level of frequency distortion of a two-port, for example, amplification of audio signals.

At the output of the analyzer is formed by the voltage Y(t), the instantaneous values of which represent the normalized frequency response Y(surveyed quadrupole. To assess the extent of insertion frequency distortions determine what value of Y() (Y(t)) deviates from a mean value of Y(0)=1, i.e., determine the frequency response, and quantitative assessment of non-uniformity of the frequency response and, consequently, introduced distortion is either the value of Y(), which is the condition |Y()-1|=max, or coefficient of frequency distortionIf the value of Y() expressed in logarithmic units of Y[dB](0)=20lgY()|.

Unfortunately, estimation of frequency distortion obtained in this way are uninformative, as it does not take into account the form of response, as measured coordinates of the points most remote from the straight line is the ideal frequency response. The relative gain(K() - gain on frequency; (0) - gain on certain average frequency0), measured at specific points in the frequency response may not be a measure of frequency distortion. Distortion spectrum signal do not depend on the gain K(i) at a frequency ofifor which it is established that K(ihas at this point the minimum or maximum value, and depend on the type of the function K(), which shows how changing the entire amplitude range of the signal after passing through the investigated quadrupole.

Technical result achieved when using the present invention is to increase the information content of the estimates of the frequency of the claim is tel frequency distortion (option 1), containing the test signal generator and spectrum analyzer, the input of which is the entrance test meter, the test output which is the output of test signal generator, according to the invention introduced the subtraction unit, the unit selection module and an integrator whose output is the output of the meter, the output of the spectrum analyzer is connected to the first input of the subtraction unit, the second input is used to feed him a fixed voltage, the output of the subtraction unit is connected to the input of the unit selection module, the output of which is connected to the input of the integrator.

The technical result is achieved that the measuring frequency distortion (option 2), containing the test signal generator and spectrum analyzer, the input of which is the entrance test meter, the test input which is the output of test signal generator, according to the invention introduced the unit taking the logarithm, the unit selection module and an integrator whose output is the output of the meter, the output of the spectrum analyzer is connected to the input of the block taking the logarithm, the output of which is connected to the input of the unit selection module, the output of which is connected to the input of the integrator.

Brief description of graficheskiy functional diagram of the meter frequency distortion in the first embodiment, a in Fig.3 is a block diagram of the measuring device according to the second option.

Fig.1 contains a graph of the normalized frequency response Y() representing an example of the frequency response of the amplifier of audio frequencies; a constant level Y(0)=1, is equal to the relative strengthening on average frequency0and represents the ideal frequency response; a graph of the magnitude |Y()-1|.

Functional diagram according to Fig.2 comprises a generator 1 of the test signal, the test amplifier 2 with a connected load of RL, spectrum analyzer 3, the subtracting unit 4, unit 5 selection module and the integrator 6. The output of the generator 1 is connected to the input of the test amplifier 2, the output of which is connected to the input of the spectrum analyzer 3, the output of which is connected to the first input of the subtracting unit 4, to the second input of which is applied a constant voltage level “1”, the output of the subtracting unit 4 is connected to the input unit 5 selection module, the output of which is connected to the input of the integrator 6,which is the meter output.

Functional diagram according to Fig.3 comprises a generator 7 of the test signal, the test amplifier 8 connected with naked is nerator 7 is connected to the input of the test amplifier 8, the output of which is connected to the input of the spectrum analyzer 9, the output of which is connected to the input unit 11, the selection module, the output of which is connected to the input of the integrator 12, the output of[dB]which is the meter output.

As an integral criterion for evaluating the linearity of the frequency response accepted functionality(Y()) that determines the distance between the compared values Y() and Y(0)=1:

where [1;2] - operating frequency range of the investigated two-port network, in this case, the test of the amplifier.

Qualitative essence(Y()) it is easy to understand if you refer to a geometric illustration of the expression (1) (Fig.1). The total area of the shaded areas of figures formed due to the non-ideal frequency response, is numerically equal to the value of the functional(Y()) designed to quantitatively take into account the whole set of frequency distortion, which depends from>], and the function Y(or, more specifically, how it is different from the values Y(0). By analogy with the applied theory amplifiers term is the square of the gain functionality(Y()) could be called the square of frequency distortion. Of course, the minimum distortion must meet the minimum of the expression (1) is the minimum area, and the condition(Y())=0 corresponds to the ideal situation of complete lack of frequency distortion.

The principle of operation of the meter (Fig.2) is quite simple and consists in the formation of a spectrum analyzer 3 signal Y(t) representing the function Y(as the scan time and then calculating the square of the frequency distortion according to the formula

where [t1; t2] - time signal Y(t).

The calculation of the integral (2), including the calculation pointering expression occurs sequentially in blocks 4, 5 and 6. (In the simplest case, the block 5 may be made under the scheme a full-wave rectifier.) It should be emphasized bound on the input unit 4. So, if the value of the function Y(0) corresponds to Y(t)=1, then input wichitaeagle (second input unit 4) you should also apply a fixed voltage of 1 V.

The relative gain and the ratio of the frequency distortion can be expressed in logarithmic units - in some cases it facilitates the perception of the data, as well as their cumulative records. In this case, to maintain consistency of terminology and the square of the frequency distortion should be expressed in logarithmic units:

Given that lgY(0)=0, since Y(0)=1, then the above expression will be simplified and takes the form

Functional diagram of the device that implements the algorithm (3) in the time domain, shown in Fig.3. As you can see, unlike the first variant according to Fig.2 is merely in the replacement block 4 subtraction block 10 taking the logarithm. In this scheme, the output will be the obtained value of[dB](Y(t)) is the square of the frequency distortion, expressed in the units [dB×Hz] (subscript index for brevity, the unit of measure is indicated conventionally, the th nature of the signal Y(t) at the output of the spectrum analyzer 3 (9). The voltage Y(t) must not be repeated many times, if not provided by the possibility of a periodic reset of the integrator 6 (12), otherwise the output voltage of the integrator will continue to increase. Therefore, during one session of measurement at the output of the spectrum analyzer 3 (9) the voltage Y(t) should appear only once in the form of a pulse with a form that displays Y(). To implement this requirement in various ways, depending on the type of the used spectrum analyzer and test stimuli. For example, if the generator 1 (7) use a sweep generator, controlled by the sawtooth generator, it is sufficient as a last apply phantastron operating in standby mode. Then the session is to begin with a single pulse received at the trigger input phantastron, and end after the end of the process of forming the voltage at the output of integrator 6 (12). To start a new session integrator 6 (12) must be zero (in the diagrams in Fig.2, figs.3 circuit reset not shown).

It should also be noted that the voltage at the output of the spectrum analyzer 3 (9), must repeat the instantaneous values exactly extrenalization gives the non-normalized values and only proportional To(), the specified value should be further divided into K(0) - gain, measured by the average frequency0. Instead of splitting you can use more simple, fairly well-known method, consisting in a preliminary calibration of the tract, which includes the test amplifier. In this case, to obtain the normalized values Y(t), the input signal of the spectrum analyzer output signal of the tested amplifier) should be pre-scaled (to weaken or strengthen; usually have to loosen), so that at a frequency of0the gain of the circuit: the tested amplifier - attenuator would be one. The attenuator in this case performs the function of an adjustable divider output voltage of the tested amplifier and is usually part of the spectrum analyzer in which it is necessary to provide the control voltage at the output of the attenuator to set the desired gain.

Measuring the area of a frequency distortion using the considered devices (Fig.2, 3), arising, for example, audio amplifiers, in contrast to about Dealey, as a quality indicator associated with the psychoacoustic features of auditory perception. The General dimensions, particularly the width, of possible failures and recoveries response, allows you to bind the visibility of the frequency distortions of their objective technical assessment, measured as the value of the functional(Y()). Moreover, it should be emphasized that the frequency dependence of the distortion on the width of the bands for which Y()1, installed long enough [Glukhov A. A. fundamentals of sound broadcasting. M: Communications, 1977, pages 38-39], and it is known that if a relatively wide spectral band dips or rises response will result in corresponding subjective sensations even at the level of 5 dB, the narrow peaks and dips even at the level of 15 dB may not always be noticeable to the ear.

Claims

1. Meter frequency distortions that contains the test signal generator and spectrum analyzer, the output of which is the entrance test meter, the test output which is the output of test signal generator, characterized in that it introduced the subtraction unit, the block selection modes the house block subtraction, the second input is used to feed him a fixed voltage, the output of the subtraction unit is connected to the input of the unit selection module, the output of which is connected to the input of the integrator.

2. Meter frequency distortions that contains the test signal generator and spectrum analyzer, the output of which is the entrance test meter, the test output which is the output of test signal generator, characterized in that it introduced the unit taking the logarithm, the unit selection module and an integrator whose output is the output of the meter, the output of the spectrum analyzer is connected to the input of the block taking the logarithm, the output of which is connected to the input of the unit selection module, the output of which is connected to the input of the integrator.



 

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FIELD: measurement technology.

SUBSTANCE: analyzer can be used for measuring level of frequency distortions introduced by audio channel. Analyzer has two spectrum analyzers which are used to determine signal spectra at output and input of tested four-terminal network. Input and output signal spectra are subject to normalization and are introduced into subtraction unit and later to unit for determining normalized signals difference module. Signal from unit for determining module is sent to integrator to find end value, which characterizes area of frequency distortions introduced by four-terminal network. According to another version of analyzer the module is substituted by squarer. Analysis of frequency characteristics can be performed without turning four-terminal network into special measuring mode.

EFFECT: improved truth of information; increased precision of measurement.

2 cl, 3 dwg

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