Intermodulation distortion occurs at frequencies that are the sum andor difference of integer multiples of the fundamental frequencies. These additional signals intermodulation products occur mainly in devices such as amplifiers and mixers, but to a. Harmonic distortion is not related to intermodulation distortion. 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 suspension generates distortion close to the resonance frequency fs. 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.
Intermodulation interference calculations in the land. Harel2 abstractthis paper describes experimental studies of passive intermodulation due to metalmetal. Understanding intermodulation distortion measurements. Intermodulation distortion is the result of two or more signals interacting in a non linear device to produce additional unwanted signals. A simple resistive mixing network is used to prevent interaction between the audio generators. 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 behavior in ldmos transistor.
Close3rd order intermodulation distortion measurement. Pdf threetone intermodulation distortion generated by. 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. Analysis and measurement of two tone intermodulation.
Dec 17, 2015 in this weeks shure whiteboard session, we cover the tricky topic of wireless intermodulation. Source and receiver are tuned at the different frequency range for harmonics, imd test etc. 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. Cascaded noise and intermodulationdistortion analysis all electronics generate noise, which adds to the signal and degrades the signaltonoiseratio snr.
Continuing the example of a simple hfc network, the distortion mechanisms in. Twotone, thirdorder intermodulation distortion im expresses the degree of nonlinearity of an electronic device that has a definable dynamic range, such as an. Until about the early 1990s, cellular communications had relatively low power carrier levels. Intermodulation distortion is the result of two or more signals interacting in a non lineardevice to produce additional unwanted signals.
Referring to figure 11, percentage intermodulation is calculated from a and b scaled on the cro display as. Source and receiver are tuned at the same frequency range. A method for measuring transient intermodulation distortion tim. Noise factor f is the ratio of the snr at the output of a device to the snr at the input. Intermodulation distortion, timing jitter, and phase noise 2. Experimental studies of passive intermodulation in metal. Apr 14, 2016 the din intermodulation distortion technique uses a similar method. Pdf this paper describes a procedure to obtain analytical expressions for the spurious signals generated in nonlinear transmission lines with. Cascaded noise and intermodulationdistortion analysis. Normal sweep frequencyoffset sweep f1 source port 1 port 2 f1 receiver. The most bothersome in a relative narrowband system would be the intermodulation products, as they often appear in band. Chapter 1 starts by addressing the intermodulation distortion problem, in the most general terms, and from a systems perspective. We are taking all precautions and following all guidelines as. When distortion is discussed, many think only of harmonic distortion.
Interaction of intermodulation products between dut and. 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 distortion or imd has always existed in rf transmission paths. Intermodulation interference calculations in the landmobile. 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. 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.
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. Passive intermodulation distortion in connectors, cable. 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. How to avoid aliasing intermodulation distortion aid the. Pim in the transmission path degrades quality of the wireless communication system. The effect will be observed on the weaker input signal. The most prominent during a two tone test would be the intermodulation products at 2f1f2, 2f2f1 and third harmonics at 3f1 and 3f2. Minimization of intermodulation distortion in gaas mesfet smallsignal amplifiers article pdf available in ieee transactions on microwave theory and techniques mtt379. Force factor blx generates significant intermodulation throughout the audio band. Chapter 21 sources of thirdorder intermodulation distortion in. Abstract an analysis of the intermodulation distortion imd behavior of ldmos transistor amplifiers is presented. Analysis of intermodulation distortion in ofdm based. Often abbreviated imd, it is an important metric of linearity for a. Second order sidebands around the high frequency tone are spaced at a frequency equal to the lowfrequency tone fh fl.
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. Intermodulation distortion in passive devices was not necessarily a problem because the distortion levels were significantly below the noise floor of the broadcast system. 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. Spectrum of multitone burst and nonlinear distortion byproducts a. Introduction the theories and operations of intermodulation distortion imd are well understood. Cascaded noise and intermodulation distortion analysis all electronics generate noise, which adds to the signal and degrades the signaltonoiseratio snr. Intermodulation is caused by nonlinear behavior of the collective signal processing physical equipment or even algorithms being used. Until five years ago, most connector engineers had never heard of the phenomenon. The generation and mitigation of these intermodulation products are described in the following sections in more detail. It is one of the key metrics in categorizing the linearity of active and passive electronic components and devices. The intermodulation distortion imd performance of 1 wideband, dccoupled amplifiers is a relatively new area for integrated operational amplifier suppliers.
Passive intermodulation distortion pim was of little concern to the connector designer. 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. How does intermodulation distortion occur, what are the. Rf amplifiers engineering notes, rf amplifiers technical reference material. 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. Aes elibrary intermodulation distortion listening tests. 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. The figure above illustrates the interpretation of the multitone distortion measurement applied to a woofer system. Multitone intermodulation distortion performance of 3rd. Difference between cross modulation and intermodulation. Can be used for harmonics or intermodulation distortion imd measurements with the vna. 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. 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 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.
Pdf thirdorder intermodulation distortion and harmonic. New progresses in ic technology extend the application of op amps where some years ago discrete circuits played the major role. Imd measurement with e5072a ena series network analyzer. Third order intermodulation distortion effect on the constellation error in rf transmitter of ieee 802. A two tone input signal produces harmonic distortion and intermodulation distortion.
The cross modulation is the intermodulation distortion caused by multiple carriers within the same bandwidth. Analog filter banks with low intermodulation distortion martin. Here is a shot of the peak of a sine wave clipped off, all by itself and its spectrum. Intermodulation distortion % intermodulation products clc.
Application note an insight intermodulation distortion measurement methods using the ifr 2026ab multisource generator. The stimulus is a strong lowfrequency interfering signal f1 combined with a weaker high frequency signal of interest f2. Introduction intermodulation distortion imd is a common problem in a variety of areas of electronics. Thirdorder intermodulation distortion due to dynamic selfheating is a well. Passive intermodulation distortion can interfere with intended communications signals limiting the capacity and range of a communications system. This can happen when strong nearby unwanted am signal gets added with the wanted am signal. Passive intermodulation distortion in radio frequency communication systems. It is shown that the turnon region abruptness compared to most other devices is important for explaining measured imd behavior such as sweetspots. Improve twotone, thirdorder intermodulation testing. 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 is one of the most interesting signal analyzer measurements. 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. Pdf minimization of intermodulation distortion in gaas.
Pdf third order intermodulation distortion effect on the. 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. Figure 10 test for audio intermodulation distortion using cro display. 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. 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.
What is imd intermodulation distortionimd is the amplitude modulation of signals containing two or more different frequencies, caused by nonlinearities in a system. Chapter 2 deals with nonlinear distortion characterization from a practical point of view. 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. Then, details on the measurement technique will be given. Nov 24, 2017 intermodulation is a phenomenon of combining undesired frequency components within an active system or from an external source. 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. In a communications system, this means that signals in one channel can cause. While the stiffness nonlinearity can not produce significant intermodulation, the other nonlinearities generate wideband distortion which can not be detected by a harmonic. Third order distortion causes multiple unwanted products.957 51 102 530 917 1469 1488 970 81 790 1494 1408 1553 384 698 759 1338 1564 111 1179 1433 1113 281 1214 1347 740 321 782 86 444 669 1555 1433 284 703 1280 729 62 599 287 1123 1351 728 546