RU2799392C1 - Device for measuring transient intermodulation distortion of an electrical signal - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: device for measuring transient intermodulation distortion of an electrical signal belongs to the field of instrumentation and is designed to detect and evaluate transient intermodulation distortion introduced by audio frequency signal amplifiers, in particular preamplifiers and power amplifiers, made in both discrete and integrated versions, and mixed techniques. The switching of the phase inverter is carried out by an introduced electronic switch, which includes two controlled electronic keys and an adjustable adder, the first electronic key is connected to the output of the phase inverter, and the second to the output of the first matching unit introduced at the input of the phase inverter, the signals from the outputs of the electronic keys are fed to the corresponding inputs of the adjustable adder, the output of which forms the output of the electronic switch and the output of the entire switched phase inverter, the operation of the electronic keys is controlled by the introduced control signal generation unit, which contains a series-connected second matching unit joined to the output of the phase inverter, a D-trigger, a third matching unit and a tunable programmable counter, output counter signal directly controls the operation of the first electronic switch, while the operation of the second electronic switch controls the output signal of the logic inverter connected to the output of the counter.

EFFECT: expanding the functionality of the unit.

1 cl, 2 dwg

Description

Technical field

The invention relates to the field of instrumentation and is intended to identify and evaluate transient intermodulation distortion introduced by audio frequency signal amplifiers, in particular pre-amplifiers and power amplifiers, made both in discrete and integrated versions, and in mixed technology.

The purpose of the invention is to expand the functionality of the device.

This is achieved by concretizing and complicating the structure of the switched phase inverter to introduce its features such as level control and change in the phase inversion frequency of the measuring signal applied to the input of the device under test, for which the phase inverter is switched by an introduced electronic switch, which includes two controlled electronic switches and an adjustable adder, the first electronic key is connected to the output of the phase inverter, and the second - to the output of the first matching unit introduced at the input of the phase inverter, the signals from the outputs of the electronic keys are fed to the corresponding inputs of the adjustable adder, the output of which forms the output of the electronic switch and the output of the entire switched phase inverter, control of the operation of electronic keys is implemented by the introduced control signal generation unit, containing a second matching unit connected in series, connected to the output of the phase inverter, a D-trigger, a third matching unit and a tunable programmable counter, the output signal of the counter directly controls the operation of the first electronic switch key, while controlling the operation of the second the electronic key carries out the output signal of the logical inverter connected to the output of the counter.

Description of analogues

A similar solution for the same purpose is a device that implements a method for measuring dynamic intermodulation distortion of an electrical signal [1, p. 4.6.4, fig. 14]. The device contains an adder, the first input of which is connected through the first switch to a sinusoidal signal generator, the second input of the adder is connected to the output of the low-pass filter, the input of the low-pass filter is connected to the rectangular signal generator through the second switch, the input of the measured amplifier and the first voltmeter, a second voltmeter, a spectrum analyzer and a load dummy are connected to the output of the measured amplifier.

The presence in the superposition of the input signal of the measured amplifier of a rectangular signal, which has sharp positive and negative drops, and therefore has a wide spectrum, makes it possible to investigate the frequency dependence of the amplitude nonlinearity of the measurement object, since causes the appearance of intermodulation products in the spectrum of the distorted signal, the intensity of which is measured using a spectrum analyzer and further calculation of the distortion coefficients.

Criticism of the analogue

The reasons preventing the achievement of the required technical result of the known device include, firstly, the use of a measuring signal of complex shape, containing the sum of two unrelated components, and secondly, the need for an indirect and time-consuming measuring procedure, as well as the complexity of calculations to obtain quantification of distortions.

Description of the prototype

The closest solution to the same purpose in terms of a set of features is a device that implements a method for measuring transient intermodulation distortion using a sawtooth signal with a frequency of 30 kHz, the phase of which is inverted at a low frequency.

The device for implementing this method contains a sawtooth signal generator connected in series, a switched phase inverter, a high-pass filter shunted by the first switch, a device under test, a low-pass filter shunted by the second switch, and a calibrated oscilloscope [2 - prototype].

The device uses a single-component signal as a measurement signal, and the procedure for obtaining a quantitative estimate of distortion is relatively simple and is carried out using a calibrated oscilloscope.

Criticism of the prototype

The reasons hindering the achievement of the required technical result when using a known device taken as a prototype include the fact that, despite the simplicity of the measuring procedure and the calculation of the distortion criterion, the device does not provide the ability to change the level of the measuring signal applied to the input of the device under test, which is important when testing devices with different nominal input levels. Also, the known device is not allowed to change the phase inversion frequency of the sawtooth signal, which may be required in the practical implementation of the measurement procedure in relation to a particular device under test.

The essence of the invention

The problem to be solved by the invention is to expand the functionality of the device.

This problem is solved by achieving a technical result in the implementation of the invention, which consists in concretizing and complicating the structure of a switched phase inverter to introduce such features as level control and changing the frequency of the phase inversion of the measuring signal.

The specified technical result in the implementation of the invention is achieved by the fact that the switching of the phase inverter is carried out by an introduced electronic switch, which includes two controlled electronic keys and an adjustable adder, the first electronic key is connected to the output of the phase inverter, and the second to the output of the first matching unit introduced at the input of the phase inverter, signals from the outputs of the electronic keys are fed to the corresponding inputs of the adjustable adder, the output of which forms the output of the electronic switch and the output of the entire switched phase inverter, the operation of the electronic keys is controlled by the introduced control signal generation unit, which contains a second matching unit connected in series connected to the output of the phase inverter, D-trigger , a third matching unit and a tunable programmable counter, the output signal of the counter directly controls the operation of the first electronic switch of the switch, while the operation of the second electronic switch controls the operation of the logical inverter connected to the output of the counter.

The analysis of the level of technology carried out by the applicant, including a search for patent and scientific and technical sources of information, made it possible to establish that the applicant did not find analogues characterized by features identical to all essential features of the claimed invention, and the definition of the identified analogues of the prototype as the closest in terms of set of features , made it possible to determine the totality of features essential in relation to the technical result in the claimed device, set forth in the claims.

Therefore, the claimed invention meets the requirement of "novelty" of the current legislation.

List of drawing figures

In FIG. 1 shows the generated measuring signal.

In FIG. 2 shows a block diagram of a device that implements the proposed device, where 1 is a sawtooth signal generator; 2 - switched phase inverter; 3 - high pass filter; 4 - the first switch; 5 - tested device; 6 - low-pass filter; 7 - the second switch; 8 - calibrated oscilloscope; 9 - the first matching block; 10 - electronic switch; 11 - the first controlled electronic key; 12 - second controlled electronic key; 13 - adjustable adder; 14 - control signal generation unit; 15 - second matching block; 16 - D-trigger; 17 - third matching block; 18 - tunable programmable counter; 19 - logical inverter; 20 - complicated switched phase inverter.

Information confirming the possibility of carrying out the invention

Information confirming the possibility of carrying out the invention to obtain the specified technical result is as follows.

The signal generated by the sawtooth signal generator (1) has a high repetition rate of 30 kHz, while the signal has a short decay time (of the order of 30 ns). The switched phase inverter (2) inverts the phase of the signal with a frequency hundreds of times smaller - about 100 Hz (30 kHz/256). The shape of the measuring signal is shown in Fig. 1. The signal has a wide spectrum, covering the entire audio range. The high-pass filter (3), having the ability to be excluded from the circuit using the first switch (4), cuts off the low-frequency part in the range of 0-2 kHz from the measuring signal band, thereby excluding low-frequency and constant components from the signal spectrum.

The excitation of transient intermodulation distortions in the device under test (5) is due to the presence of a “fast” edge in the form of a sawtooth signal, which for several hundred signal repetition periods is a positive drop, and after its inversion is negative. At the output of the device under test (5), with the help of a low-pass filter (6), which has the ability to be excluded from the circuit using the second switch (7), measurement information is allocated in the frequency range of 0-2 kHz.

The procedure for obtaining a quantitative estimate of distortion is relatively simple and comes down to finding the ratio of two values determined using a calibrated oscilloscope (8), one of the values is determined with filters 3 and 6 turned off, the second - with filters 3 and 6 connected.

The introduction of the first matching unit (9) into the structure of the device eliminates the mutual influence of the output circuit of the generator (1) and the input circuit of the switched phase inverter (2), which is especially significant at the moments of the phase inversion of the sawtooth signal. The phase inversion of the signal occurs due to the periodic connection and disconnection of the phase inverter (2) from the measuring path using the introduced electronic switch (10), while switching its controlled first (11) and second (12) electronic keys is carried out by the introduced block (14) for generating control signals .

The key operation control signal is formed from the output signal of the phase inverter (2), to the output of which the second matching unit (15) is connected, which serves to match the analog and logic parts of the unit (14). The D-trigger (16) responds to positive signal drops by generating square-wave clock pulses at its output with a repetition rate of 30 kHz. Further, the pulses through the third matching block (17) are fed to the input of a tunable programmable counter (18), the conversion factor of which can vary from 1 to 256.

The output low-frequency signal of a rectangular shape from the output of the counter (18) is fed to the first controlled electronic key (11). To generate a control signal for the second electronic key (12) operating in antiphase with the first one, the counter signal (18) is fed to the logic inverter (19).

The adjustable adder (13) forms the final form of the measurement signal, while allowing its level to be changed before being fed either to the input of the high-pass filter (3) or to the input of the device under test (5), as required by the measurement procedure.

The introduced blocks form the structure of a complicated switched phase inverter (20).

If the output signal of the device under test (5) has transient intermodulation distortion, a low-frequency square wave signal will appear at the output of the low-pass filter (6). The swing of a rectangular signal, fixed on the scale of the oscilloscope, will be proportional to the amount of distortion introduced. To obtain a relative quantitative estimate of the distortions introduced by the device under test, the amplitude of the rectangular signal should be compared with the signal amplitude at the output of the device under test (5) with filters (3) and (6) disabled, taken as 100%.

The proposed device has extended functionality that allows you to change the parameters of the measuring signal in accordance with the characteristics of a particular device under test, than to ensure its operation under nominal measurement conditions. Thus, the possibility of adjusting the level of the signal applied to the input of the device under test will make it possible to achieve distortions in its output signal, and the introduced possibility of changing the phase inversion frequency of the sawtooth signal during the formation of the measuring signal will make it possible to take into account and eliminate such features of the device under test as the probability of an oscillatory process occurring at the fronts of a rectangular signal at the output of the low-pass filter, which is associated with the peculiarities of the shape of the frequency response of the device under test, which is prone to self-excitation. Increasing the frequency of the phase inversion of the measuring signal will allow leveling the oscillogram and simplifying the acquisition of measurement results.

Concretization of the structure of such an important unit of the device as a switched phase inverter, with the introduction of the possibility of adjusting the parameters of the measuring signal, makes the device as a whole more multifunctional in practical application.

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

- a device embodying the claimed invention in its implementation is intended for use in the field of control and measurement technology and is intended to detect and evaluate transient intermodulation distortion introduced by audio frequency signal amplifiers, in particular preamplifiers and power amplifiers, made both in discrete and in integrated versions, and in mixed technology;

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

- a device embodying the claimed invention 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. GOST 23849-87. HOUSEHOLD RADIO-ELECTRONIC EQUIPMENT. Methods for measuring the electrical parameters of audio signal amplifiers. - M.: Ed. standards, 1990 (rev. with changes), p. 4.6.4, fig. 14.

2. Fildmann L. Measuring TIM Distortion. Radio-Electronics, June, 1979 - prototype.

Claims (1)

A device for measuring transient intermodulation distortions of an electrical signal, containing a sawtooth signal generator connected in series, a switched phase inverter, a high-pass filter shunted by the first switch, a device under test, a low-pass filter shunted by the second switch, and a calibrated oscilloscope, characterized in that the phase inverter is switched the introduced electronic switch, which includes two controlled electronic keys and an adjustable adder, the first electronic key is connected to the output of the phase inverter, and the second - to the output of the first matching unit introduced at the input of the phase inverter, the signals from the outputs of the electronic keys are fed to the corresponding inputs of the adjustable adder, the output which forms the output of the electronic switch and the output of the entire switched phase inverter, the operation of the electronic keys is controlled by the introduced block for generating control signals, containing a second matching block connected in series connected to the output of the phase inverter, a D-trigger, a third matching block and a tunable programmable counter, the output signal of the counter directly controls the operation of the first electronic key of the commutator, while the operation of the second electronic key controls the output signal of the logic inverter connected to the output of the meter.

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