Intermodulation distortion is the result of two or more signals interacting in a non linear device to produce additional unwanted signals. It is made more difficult by the fact that this has to be done in the absence of other kinds of distortion such as harmonic and transient intermodulation. Apr 14, 2016 the din intermodulation distortion technique uses a similar method. The even and odd order intermodulation distortion imd were both measured at the resonant frequency of the patterned devices using the threetone intermodulation distortion method developed by our. Continuing the example of a simple hfc network, the distortion mechanisms in. Close3rd order intermodulation distortion measurement. Thirdorder intermodulation distortion due to dynamic selfheating is a well. These additional signals intermodulation products occur mainly in devices such as amplifiers and mixers, but to a.
Analysis and measurement of two tone intermodulation. Pdf minimization of intermodulation distortion in gaas. Intermodulation is caused by nonlinear behavior of the collective signal processing physical equipment or even algorithms being used. Improve twotone, thirdorder intermodulation testing. Referring to figure 11, percentage intermodulation is calculated from a and b scaled on the cro display as. Intermodulation distortion occurs at frequencies that are the sum andor difference of integer multiples of the fundamental frequencies. Third order intermodulation distortion effect on the constellation error in rf transmitter of ieee 802. Harel2 abstractthis paper describes experimental studies of passive intermodulation due to metalmetal. Noise factor f is the ratio of the snr at the output of a device to the snr at the input. Abstract an analysis of the intermodulation distortion imd behavior of ldmos transistor amplifiers is presented. Intermodulation distortion from receiver non linear phase characteristics final report tasks i and ii of radio communications study on noise threshold reduction contract nas 59742 december 2, 1966 prepared for national aeronautics and space administration goddard space flight center greenbelt, maryland c. The stimulus is a strong lowfrequency interfering signal f1 combined with a weaker high frequency signal of interest f2. Passive intermodulation distortion in radio frequency communication systems.
Not all interference is a result of intermodulation distortion. Often abbreviated imd, it is an important metric of linearity for a. The most prominent during a two tone test would be the intermodulation products at 2f1f2, 2f2f1 and third harmonics at 3f1 and 3f2. Intermodulation interference is the undesired combining of several signals in a nonlinear device, producing new, unwanted frequencies, which can cause interference in adjacent receivers located at repeater sites. Pdf this paper describes a procedure to obtain analytical expressions for the spurious signals generated in nonlinear transmission lines with. Minimization of intermodulation distortion in gaas mesfet smallsignal amplifiers article pdf available in ieee transactions on microwave theory and techniques mtt379. Rf amplifiers engineering notes, rf amplifiers technical reference material. Linear parameter measurement lpm lpm module uses a multitone complex as stimulus which may be used for distortion measurement in a separate microphone channel multitone measurement mton mton module provides an automatic multitone measurement sequence to reach the maximum spl below a multitone distortion threshold. Intermodulation interference calculations in the landmobile. Analysis of intermodulation distortion in ofdm based. This can happen when strong nearby unwanted am signal gets added with the wanted am signal. The most bothersome in a relative narrowband system would be the intermodulation products, as they often appear in band. Aes elibrary intermodulation distortion listening tests. Chapter 1 starts by addressing the intermodulation distortion problem, in the most general terms, and from a systems perspective.
The figure above illustrates the interpretation of the intermodulation distortion measurement using a fixed low frequency tone f 1 and a high frequency tone f 2 which is varied over the audio band voice tone sweep. When distortion is discussed, many think only of harmonic distortion. Nov 24, 2017 intermodulation is a phenomenon of combining undesired frequency components within an active system or from an external source. How does intermodulation distortion occur, what are the. Interaction of intermodulation products between dut and.
Intermodulation distortion is one of the most interesting signal analyzer measurements. Intermodulation interference calculations in the landmobile service 19952007 scope this recommendation serves as a basis for the calculation of a maximum of three intermodulation interference that are created at the output of a receiver under influence of intensive unwanted signals at. We are taking all precautions and following all guidelines as. Intermodulation distortion or imd has always existed in rf transmission paths. Intermodulation interference calculations in the land. Intermodulation distortion, timing jitter, and phase noise 2. How to avoid aliasing intermodulation distortion aid the. Cascaded noise and intermodulationdistortion analysis.
The intermodulation distortion imd performance of 1 wideband, dccoupled amplifiers is a relatively new area for integrated operational amplifier suppliers. The intermodulation between frequency components will form additional components at frequencies that are not just at harmonic frequencies integer multiples of either, like harmonic distortion, but. Intermodulation distortion behavior in ldmos transistor. Understanding intermodulation distortion measurements. Dec 17, 2015 in this weeks shure whiteboard session, we cover the tricky topic of wireless intermodulation. The suspension generates distortion close to the resonance frequency fs. Intermodulation distortion is the result of two or more signals interacting in a non lineardevice to produce additional unwanted signals. Force factor blx generates significant intermodulation throughout the audio band. 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.
Source and receiver are tuned at the same frequency range. Second order sidebands around the high frequency tone are spaced at a frequency equal to the lowfrequency tone fh fl. A is the power amplifier having an openloop gain of ao, p is the purely resistive feedback path around it, and c is the preamplifier. 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. Until five years ago, most connector engineers had never heard of the phenomenon. A simple resistive mixing network is used to prevent interaction between the audio generators. Cascaded noise and intermodulationdistortion analysis all electronics generate noise, which adds to the signal and degrades the signaltonoiseratio snr. The generation and mitigation of these intermodulation products are described in the following sections in more detail. Intermodulation distortion is the result of two or more signals interacting in a non. Intermodulation distortion in passive devices was not necessarily a problem because the distortion levels were significantly below the noise floor of the broadcast system. What is imd intermodulation distortionimd is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities in a system. Passive intermodulation distortion in connectors, cable. The effect will be observed on the weaker input signal.
Source and receiver are tuned at the different frequency range for harmonics, imd test etc. 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. Whats the relationship between harmonic distortion and. While some studies have shown that human perception is extremely sensitive to intermodulation distortion for much of the spectrum of human hearing, the audibility of intermodulation distortion in low frequencies was thought to be equal or less than that of harmonic distortion by. Pim in the transmission path degrades quality of the wireless communication system. Passive intermodulation pim is a form of intermodulation distortion that occurs in passive components such as antennas, cables, connectors, or duplexers with two or more highpower input signals.
Pdf threetone intermodulation distortion generated by. Pdf third order intermodulation distortion effect on the. Now, due to the frequency plans of todays modern base stations, the use of higher transmitter power levels and more sensitive receivers, pim has surfaced. Intermodulation interference calculations in the landmobile service 19952007 scope this recommendation serves as a basis for the calculation of a maximum of three intermodulation interference that are created at the output of a receiver under influence of intensive unwanted signals at the. A method for measuring transient intermodulation distortion tim eero leinonen, matti otala, and john curl technical research centre of finland, electronics laboratory, sf90101 oulu, finland a description of the squaresine intermodulation measuring method is given. A two tone input signal produces harmonic distortion and intermodulation distortion. Can be used for harmonics or intermodulation distortion imd measurements with the vna. Figure 10 test for audio intermodulation distortion using cro display. Twotone, thirdorder intermodulation distortion im expresses the degree of nonlinearity of an electronic device that has a definable dynamic range, such as an. Combination of two or more signals will create another signal which may fall into another frequency band of the system and cause interference to the system. Cascaded noise and intermodulation distortion analysis all electronics generate noise, which adds to the signal and degrades the signaltonoiseratio snr. Multitone intermodulation distortion performance of 3rd. 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.
Analog filter banks with low intermodulation distortion martin. Passive intermodulation distortion can interfere with intended communications signals limiting the capacity and range of a communications system. Application note an insight intermodulation distortion measurement methods using the ifr 2026ab multisource generator. Introduction intermodulation distortion imd is a common problem in a variety of areas of electronics. Introduction the theories and operations of intermodulation distortion imd are well understood. While the stiffness nonlinearity can not produce significant intermodulation, the other nonlinearities generate wideband distortion which can not be detected by a harmonic. 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. 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. Intermodulation im or intermodulation distortion imd is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities or time variance in a system. Until about the early 1990s, cellular communications had relatively low power carrier levels. Experimental studies of passive intermodulation in metal. Here is a shot of the peak of a sine wave clipped off, all by itself and its spectrum. Then, details on the measurement technique will be given. A method for measuring transient intermodulation distortion tim.
Third order distortion causes multiple unwanted products. It is shown that the turnon region abruptness compared to most other devices is important for explaining measured imd behavior such as sweetspots. Pdf thirdorder intermodulation distortion and harmonic. Difference between cross modulation and intermodulation. 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. Twotone intermodulation testing a convenient way to measure imd is to combine two equal power signals with a set frequency spacing at the input of the deviceundertest dut. New progresses in ic technology extend the application of op amps where some years ago discrete circuits played the major role. Normal sweep frequencyoffset sweep f1 source port 1 port 2 f1 receiver. Spectrum of multitone burst and nonlinear distortion byproducts a. Imd measurement with e5072a ena series network analyzer. 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.
Chapter 21 sources of thirdorder intermodulation distortion in. Passive intermodulation distortion pim was of little concern to the connector designer. The cross modulation is the intermodulation distortion caused by multiple carriers within the same bandwidth. 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. Intermodulation distortion % intermodulation products clc. Harmonic distortion is not related to intermodulation distortion. It is one of the key metrics in categorizing the linearity of active and passive electronic components and devices. In a communications system, this means that signals in one channel can cause. Here is another point i make, if you remove part of a sine wave, the harmonic spectrum exactly matches the harmonic content of that feature. Chapter 2 deals with nonlinear distortion characterization from a practical point of view.
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