Meter frequency distortion
The meter is designed to determine the level of frequency distortion of a two-port, such as audio amplifiers. 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 Quad. The output of the Quad is connected to the input of the integrator. Quantitative assessment criterion frequency distortion is the square of the frequency distortion resulting from the integration. The meter allows you to enhance the usefulness of the evaluation of the frequency distortion of a quadrupole in the original signal. 1 Il.
The invention relates to the field of radio, and is intended for integral assessment of the level of frequency distortion of a two-port, such as audio amplifiers.
The prototype is the analyzer's amplitude-frequency characteristics (AFC), consisting of the generator is the first output of which serves as the output test signal generator, and the test input is the input of the spectrum analyzer [Rosenberg, C. I. methods of measurement of Radio parameters of processes and systems M.: Publishing house of the Committee of standards, measures and measuring instruments, 1970, pp. 123-124].
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 distortion
Unfortunately, estimation of frequency distortion obtained in this way are uninformative, as it does not take into account the form of response, but are determined only coordinates of the points most remote from the straight line is the ideal frequency response. The relative gain(K(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 has been established that(ihas at this point the minimum or maximum value, and depend on the type of functions K(), which shows how the entire amplitude range of the signal after passing through the investigated quadrupole.
Technical result achieved when using the present invention is to improve the informativeness evaluation of frequency distortion of a quadrupole in the original signal.
The technical result is achieved that the measuring frequency distortions that contains 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 a subtraction unit, a squarer and an integrator, the output of which is what is used to feed him a fixed voltage, the output of the subtraction unit is connected to the input of the Quad, the output of which is connected to the input of the integrator.
The invention is illustrated by the drawing, which shows a functional diagram of the meter frequency distortions.
The functional circuit comprises a generator 1 of the test signal, the test amplifier 2 with a connected load of RL, spectrum analyzer 3, block 4 subtraction, Quad splitter 5 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 of the Quad 5, the output of which is connected to the input of the integrator 6,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 [1if the test of the amplifier.
Of course, the minimum distortion must correspond at least(Y(), and the condition(Y())=0 corresponds to the ideal situation of complete lack of frequency distortion.
The computation of the value of(Y() changes the nature of the measure of frequency distortion. Unlike those estimates, the proposed parameter allows to take into account the shape of the frequency response and to evaluate the distortion along two dimensions: frequency and relative amplitude. Integral assessment(Y()) is the characteristic quality of the actual device, as in the case of audio amplifiers allows you to get an objective technical indicator associated with the psychoacoustic features of auditory perception.
The principle of operation of the meter 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
0) corresponds to Y(t)=1, then input wichitaeagle (second input unit 4) you should also apply a fixed voltage of 1 V.
As the feature of the meter should highlight the nature of the signal Y(t) at the output of the spectrum analyzer 3. The voltage Y(t) must not be repeated many times, if not provided by the possibility of a periodic reset of the integrator 6, 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 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 to use a sweep generator, controlled by the sawtooth generator, dostatus 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 the integrator 6. To start a new session integrator 6 must be reset (the reset circuit not shown).
It should also be noted that the voltage at the output of the spectrum analyzer 3 must repeat the instantaneous values are just the normalized frequency response, and not frequency-dependent gain. To obtain the function Y(t) if the spectrum analyzer generates 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. Attenuata is commonly included in the spectrum analyzer, where it is necessary to provide the control voltage at the output of the attenuator to set the desired gain.
Meter frequency distortions that contains 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, characterized in that it introduced a subtraction unit, a squarer 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 Quad, the output of which is connected to the input of the integrator.
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.
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