Intermodulation distortion article about intermodulation. Jul 14, 2011 intermodulation distortions any distortions that contain frequencies that were not present in the initial input signal are called harmonic distortions. Rf amplifiers engineering notes, rf amplifiers technical reference material. Close3rd order intermodulation distortion measurement. The example contains a typical setup to perform harmonic distortion measurements thd, snr, sinad. Referring to figure 11, percentage intermodulation is calculated from a and b scaled on the cro display as. Higher harmonics and intermodulation products are not labeled. Nonlinear distortion characterized by the appearance of output frequencies equal to the sums and differences of integral multiples of the input frequency components. Not all interference is a result of intermodulation distortion. Not only can a spectrum analyzer be used to measure imd of a device under test dut, but a spectrum analyzer may also contribute imd through its nonlinear properties. Intermodulation distortion is a scenario where signals from outside the monitored channel combine nonlinearly to produce frequencies within monitored channel frequency range. The linear approximations are the correct 31 ratio approximately, with 1db of gain on the waveform the intermods increase by approx 3db. Interfering signals wanted distortion product now we see that even if the system is narrowband, the output of an ampli. This example shows how to select an intermediate frequency if that is free from any intermodulation distortion.
The result is an unpleasant effect known as intermodulation distortion. Analyzing mixers using intermodulation distortion analysis. If the voice coil is at the rest position x0 the instantaneous value of blx0 is maximal and generates the. Dec 16, 2011 im distortion and harmonic distortion are two pairs of shoes and must be defined individually as already shown in the short essay about myth and facts about aliasing but more on this later on. The total harmonic distortion is determined from the fundamental frequency and the first five harmonics using a modified periodogram of the same length as the input signal. Intermodulation distortion imd measurements on modern. Intermodulation distortion is the result of two or more signals interacting in a non linear device to produce additional unwanted signals. These additional signals intermodulation products occur mainly in devices such as amplifiers and mixers, but to a. The figure above shows the intermodulation of a high frequency tone f 2 by a low frequency tone f 1 caused by a nonlinear force factor blx characteristic. This test measures the 2nd and 3rd order intermodulation distortion of the analyzer using a tone separation of 0. Transient intermodulation distortion how is transient.
Provides distortion cancellation up to the 1 db compression point of the main amplifier. Nonlinear elements, nonlinear behavior, intermodulation distortion, ip2ip3, interference use these blocks to specify the nonlinear behavior of amplifiers and mixers. In a multicarrier transmission system, intermodulation distortion imd is generated because of amplifier nonlinearities. This example shows how to perform measurements using the spectrum analyzer block. This matlab function returns the total harmonic distortion thd in dbc of the realvalued sinusoidal signal x. Intermodulation distortion % intermodulation products clc. Analyze the harmonic distortion of a weakly nonlinear system in the presence of noise. This is important for operation under multitone signals or complex modulation wave. How to avoid aliasing intermodulation distortion aid the invisible distortion in digital audio if an adc the components used for the analog to digital conversion receives frequencies at more than the half samplerate, it will mirror the frequencies around the half of the sample frequency, and therefore create new aharmonic frequencies. The computation is performed over a periodogram of the same length as the input using a kaiser window with. These separations are used so the products are inband. A low range setting is used to avoid requiring a high output from the sources. Intermodulation analysis is a type of transient analysis in which two sinusoidal signals are applied to an input source and the resulting intermodulation products at the sum and difference frequencies are computed.
Intermodulation distortion analysis is a type of transient analysis. By fourier analisys, you can see that changing amplitude of a frequency actually implies additional frequencies. The central plots show dashed lines which are linear approximations. It applies two sinusoidal signals to the named input source with userspecified nonharmonic frequencies and amplitudes, and then measures the resulting second and third order distortion in the specified load resistor using the harm function. April, 1994 5 6 3 4 2 the intermodulation distortion imd performance of 1 wideband, dccoupled amplifiers is a relatively new area.
Subtraction is a linear operation, so naturally, both would have the same spectrum with the signs inverted something your magnitude plots doesnt show with the addition of the sine wave itself in the lower spect. Plot the signal spectrum and annotate the total harmonic distortion thd. Figure 10 test for audio intermodulation distortion using cro display. The dynamic intermodulation distortion products are the amplifiers were sansui 771, marantz 2270, harman often generated by tim, that is, the rapid rise of the kardon 230 a, sony ta 5650, salora 2000, dux ta. This is in contrast to im2 where the frequency of the intermodulation was at a lower and higher frequency. Such behavior includes ip2ip3, intermodulation distortion and 1db compression. The basic theory of tim is straightforward and clear l. Intermodulation distortion is the result of two or more signals interacting in a non lineardevice to produce additional unwanted signals. Aes elibrary amplitude and phase of intermodulation distortion. It is shown that amplitude intermodulation distortion aimd in a feedback amplifier is associated primarily with signalinduced changes in the lowfrequency gain of the forward path, whereas phase intermodulation distortion pimd is associated primarily with signalinduced changes in the gainbandwidth product.
Transient intermodulation distortion listed as tim. Chapter 2 deals with nonlinear distortion characterization from a practical point of view. Intermodulation distortion measurements on modern spectrum. Second order sidebands around the high frequency tone are spaced at a frequency equal to the lowfrequency tone fh fl.
Transient intermodulation distortion tim is usually measured by putting a burst of a fixed frequency into a amplifier and then measuring what actually comes out. Tim transient intermodulation distortion acronymfinder. When distortion is discussed, many think only of harmonic distortion. Tim is defined as transient intermodulation distortion frequently. A method for measuring transient intermodulation distortion. How is transient intermodulation distortion abbreviated.
Calculate intermodulation products from 2 and 3 frequencies. The percentage intermodulation distortion is defined as the percentage of amplitude modulation, represented by the second and third order pair of sidebands, of the highfrequency signal. The dynamic intermodulation distortion products are the amplifiers were sansui 771, marantz 2270, harman often generated by tim, that is, the rapid rise of the. Intermodulation distortion measurements on modern spectrum analyzers this application note describes the differences in intermodulation distortion measurements between traditional spectrum analyzers with analog narrowband if signal path and modern spectrum analyzers using a wideband if signal path and digital rbw filters. The modified periodogram uses a kaiser window with. The causes of intermodulation distortion in magnetic tape recording are discussed. It is a side effect of the use of a too strong negative feedback, which makes the modern transistor amplifiers, in particular, very susceptible to it.
The presence of imd degrades the performance of such systems. This example shows how to use the rf blockset circuit envelope library to test intermodulation distortion of an amplifier using twocarrier envelope analysis. Intermodulation or intermodulation distortion imd is the amplitude modulation of signals containing two or more different frequencies in a system with nonlinearities. Apr 14, 2016 the din intermodulation distortion technique uses a similar method. Interaction of intermodulation products between dut and. The example contains a typical setup to perform harmonic distortion measurements thd, snr, sinad, sfdr, thirdorder intermodulation distortion measurements toi, adjacent channel power ratio measurements acpr, complementary cumulative distribution function ccdf, and peak to average power ratio papr. Transient intermodulation distortion how is transient intermodulation distortion abbreviated. Rf blockset lets you simulate nonlinear rf amplifiers and model memory effects to estimate gain, noise, evenorder, and oddorder intermodulation distortion. This intermodulation distortion is a completely undesirable but unavoidable scenario in rf. In a communications system, this means that signals in one channel can cause. Second order sidebands around the high frequency tone are spaced at a frequency equal to. Theory of intermodulation distortion measurement imd application note 5c043 page 1 of 3 introduction intermodulation distortion occurs when the nonlinearity of a device or system with multiple input frequencies causes undesired outputs at other frequencies.
If the voice coil is at the rest position x0 the instantaneous value of blx0 is maximal and generates the peak in the envelope of the sound pressure signal. A simple resistive mixing network is used to prevent interaction between the audio generators. Intermodulation distortion imd plays an important role for many spectrum analyzer based measurements. It is shown that nonsymmetrical input signals can be a source of intermodulation in tape recording. The stimulus is a strong lowfrequency interfering signal f1 combined with a weaker high frequency signal of interest f2. Pdf a phase shift technique for intermodulation cancellation.
Three harmonics were used to model each of the rf signals. Intermodulation products third order from matlab and fft. The intermodulation known in the field of rf communications has nothing to do with the audiophile term, intermodulation distortion imd. A method for measuring transient intermodulation distortion tim. The concept of harmonic distortion is easy to understand you apply a clean sine wave, with very low content at its harmonic frequencies, and then analyze the output from the device you are testing for increased relative levels at those harmonic frequencies. Intermodulation distortion in large amounts produces the discordant, chimelike effect of the ring modulator. Intermodulation on the other hand is a known fact of life in the rf domain, and both active within an analog amplifier and passive rusty hardware im can cause serious emc issues. Chapter 1 starts by addressing the intermodulation distortion problem, in the most general terms, and from a systems perspective. Jan 26, 2018 the central plots show dashed lines which are linear approximations. The thd function computes the power ratio of the harmonics to the fundamental and.
Fryer distortion listeninq tests l10 introduction it is fairly simple to measure the amount of intermodulation distortion produced by loudspeakers, but it is more difficult to find out how much of this kind of distortion is found objectionable or just detectable when masked by music. It can be a tremendous job to calculate the intermodulation products from several frequencies, below is a calculator that calculates the intermodulation product from two and three frequencies. Intermodulation distortion, timing jitter, and phase noise 2. Simulation and modeling of intermodulation distortion in. Aes elibrary intermodulation distortion listening tests. The rfal technique for cancellation of distortion in power. Intermodulation distortions any distortions that contain frequencies that were not present in the initial input signal are called harmonic distortions. Tim stands for transient intermodulation distortion.
This is due to an interaction between two or more frequencies in which many signal byproducts are generated that have no direct harmonic relationship to the. Intermodulation distortion in audio is usually specified as the root mean square rms value of the various sumanddifference signals as a percentage of the original signals rms voltage, although it may be specified in terms of individual component strengths, in decibels, as is common with rf work. Im distortion and harmonic distortion are two pairs of shoes and must be defined individually as already shown in the short essay about myth and facts about aliasing but more on this later on. Efficient low intermodulation distortion configuration that doubles the output power of the main amplifier over wide input power and frequency ranges. Nonlinear elements, nonlinear behavior, intermodulation distortion, ip2ip3, interference. Twotone envelope analysis using real signals matlab. A close correlation exists between harmonic distortion and intermodulation distortion measurements when the individual orders of distortion are measured separately. These additional signals intermodulation products occur mainly in devices such as amplifiers and mixers, but to a lesser extent they also occur in passive devices such as those found in many transmission. A widely used standard for measuring intermodulation distortion is the smpte society of motion picture and television engineers standard.
968 451 439 592 1174 1402 603 1137 334 1258 911 325 615 798 778 233 1306 731 435 773 40 1079 212 868 539 555 11 547 490 523 399 681