The amount of intermodulation distortion generated depends on the density of the input spectra. It is one of the key metrics in categorizing the linearity of active and passive electronic components and devices. The practical measuring procedure is described, and measurement results of commercial audio power amplifiers and integrated operational amplifiers are presented, in many cases showing appreciable transient intermodulation in units which have excellent and total harmonic distortion and smpte intermodulation distortion. If sid only occurs for a portion of the signal, it is called transient intermodulation distortion. As with other tests described, two audio signals at different frequencies are fed through the device to be tested and the output is monitored. Audio distortion measurements university of surrey. 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. Rf amplifiers engineering notes, rf amplifiers technical reference material. Harmonics are caused by area, my article in linkedin proves it. Osa measurement of intermodulation distortion in high.
Although imd may affect many types of signal data, this definition focuses on sound. Injecting 20 tones separated by half octaves from 20hz to 20khz, then measuring distortion in. The practical measuring procedure is described, and measurement results of. Unlike traditional im distortion measurements performed on loudspeakers, this technique requires the test stimulus to be played. The results of such measurements are difficult to interpret, compare, and over lay. A more meaningful test than thd, intermodulation distortion gives a measure of. The output of the amplifier is then measured by filtering out the 60 hz part of the signal and then measuring the amount of amplitude modulation on the remaining 6.
Harmonic and intermodulation im distortion are well known examples of nonlinear distortion. Pdf a comparison of nonlinear distortion measurement methods. We encounter this problem every day trying to measure the ip3 of the t3, the worlds highest linearity mixer. Smpte din smpte imd is a technique for measuring imd intermodulation distortion according to the smpte rp1201983 standard. This video shows the onset of intermodulation distortion when moving the compressor to a postmixing point in the signal chain. A description of the squaresine intermodulation measuring method is given. 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. Audio specifications notes on the frequency spectrum. New progresses in ic technology extend the application of op amps where some years ago discrete circuits played the major role. Rf intermodulation distortion measurement two tone test. Im designing an audio amplifier and im trying to simulate and measure all the characteristic features of it output power, offset, bandwidth, inputoutput impedances, etc. The second and thirdorder intercept points ip2 and ip3 are.
Refer second vs third order intercept point basics. While the stiffness nonlinearity can not produce significant intermodulation, the other nonlinearities generate wideband distortion which can not be detected by a harmonic. Intermodulation distortion imd measures the level of unwanted combinations of different frequencies found in the input signal. Scientech 4092 comes with a calibrated monitor output for spectral analysis and visual. Introduction the theories and operations of intermodulation distortion imd are well understood. Measurement method of these intermodulation distortion imd products at 2f1f2 and 2f2f1 is known as two tone test method. Intermodulation causes spurious emissions that can create minor to severe interference to other operations on the signal. Introduction although twotone measurements still represent the industry standard in intermodulation distortion imd characterization, nowadays, engineers seek for alternative test procedures closer to the systems final operation regime. Twotone testing for imd has been used to characterize the non. Interaction of intermodulation products between dut and.
From an audio perspective, any frequencies that result from intermodulation are counted as intermodulation distortion, including sum and difference frequencies should they occur. Two measurement techniques are evaluateda standard twotone measurement and a more complicated threetone measurement technique to measure imd3. For a more indepth look at intermodulation distortion imd as it is measured in amplifying devices, see intermodulation distortion imd. This is also why we developed the pbr series of power combiners. How to avoid aliasing intermodulation distortion aid the. Maintenance engineers make them to ensure equipment is still working to specification, or to ensure that the cumulative defects of an audio path are within limits considered acceptable. Multitone intermodulation distortion performance of 3rd. Intermodulation distortion diagnostics of audio systems. Harmonic distortion and total harmonic distortion may not convey sufficient information. A model of the measurement system is developed and used to analyze the limitations of the two techniques in determining the.
Multitone intermodulation distortion testing audio. This video briefly outlines key measurements for audio products, specifically intermodulation distortion, frequency response and phase. The two interfering signals are defined using a continuous wave cw carrier and a modulated signal. Following test equipments are needed for the intermodulation distortion measurement setup. Measuring intermodulation distortion w keysight m9393a pxie vsa. Passive intermodulation distortion in connectors, cable. Introduction intermodulation distortion imd is a common problem in a vari. The intermodulation distortion imd performance of 1 wideband, dccoupled amplifiers is a relatively new area for integrated operational amplifier suppliers. Thd stands for total harmonic distortion and can be used to estimate the degree to which a system is nonlinear. Intermodulation distortion is one of the most interesting signal analyzer measurements. For receiver intermodulation measurement setups, you need one signal generator for the wanted signal, and two signal generators as interfering signals as shown in figure 3.
Passive intermodulation distortion in connectors, cable and cable assemblies reduce or eliminate the pim generated by the active devices in the system david weinstein. From a single intermodulation measurement, ip3 can be estimated using the following formula. Application note an insight intermodulation distortion measurement methods using the ifr 2026ab multisource generator. The din intermodulation distortion technique uses a similar method. The intermodulation measurement measures the third order and. Several techniques are currently in use for measuring distortion of audio equipment. 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. Intermodulation distortion imd is an important consideration in microwave and rf component design. The intermodulation distortion performance of wideband dccoupled amplifiers is an important aspect of design using operational amplifiers, especially in the field of satellite communications where the usable bandwidth for each transponder is limited and multiple signals. Intermodulation distortion is a tough thing to measure.
As the input signal becomes more complex the intermodulation distortion becomes greater, and this can be seen of a speaker measurement in figure 15, where hundreds if not thousands of spectral distortion components are generated from a handful of. Imd something new elliott sound products the audio. Graphing, interpretation, and comparison of results of. 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. Although it is feasible for a modeler to explicitly call out this distortion, its existence is normally a function of happenstance and not something the modeler can reliably predict. 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. Guidelines to designing low pim connectors and cable assemblies will be outlined including a discussion of the. This effect results from nonlinearities in your audio system. The integral of time and voltage is energy, and that energy shows up as harmonic distortion. Intermodulation im or intermodulation distortion imd is the amplitude modulation of signals. 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. Transmit intermodulation is a measure of a transmitter to inhibit the generation of intermodulation products in the presence of the modulated signal and the tone signal. Intermodulation distortion imd is a popular measure of the linearity of amplifiers, gain blocks, mixers, and other rf components.
Microphone intermodulation distortion measurement listen. Measurement of intermodulation distortion at audio frequencies. The existence of intermodulation components can affect the performance of an audio production in various ways. Whats the relationship between harmonic distortion and. Intermodulation distortion article about intermodulation. Measurements and perception of nonlinear distortioncomparing numbers and sound quality. Intermodulation distortion considerations for adcs.
Practically all audio equipment has some nonlinearity, so it will exhibit some amount. Thd total harmonic distortion in audio measurement. 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. Accurately characterizing third order intermodulation distortion imd3 in highlinearity photodiodes is challenging. Intermodulation distortion audio mixing example by dr rob. Intermodulation distortion measurements on modern spectrum.
However, i dont know how to measure intermodulation distortion imd or transient intermodulation distortion tim. Intermodulation should not be confused with general harmonic distortion which does have widespread use in audio effects processing. Understanding intermodulation distortion measurements. Imd adds components to the sound that are not found in the original signal. Intermodulation distortion may violate the limits of a spectrum mask that is modeled to contain the ideal signal. Designers take measurements so that they can specify the performance of a piece of equipment.
Often abbreviated imd, it is an important metric of linearity for a wide range of rf and microwave components. Scientech 4092 audio distortion meter tenders a minimum residual distortion and noise of 0. I have always had a vision of running a 20tone intermodulation test. Measurements that have two tones in the stimulus are used to measure imd. The most common method for indicating the amount of nonlinear distortion introduced by an audio amplifier is the total harmonic distortion thd.
Audio intermodulation distortion and frequency response. 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 high isolation allows us to measure very high ip3 values without distortion from the synthesizers affecting the measurement. We are taking all precautions and following all guidelines as. If a modern spectrum analyser is available, the relative amplitudes in decibels from all components at the output can be displayed. Chapter 6 modulation measurements, am, fm, digital, quadrature chapter 7 distortion measurements, harmonic and intermodulation distortion chapter 8 noise and noise measurements, power spectral density, equivalent noise bandwidth chapter 9 pulse measurements, pulse spectrum, pulsed rf. 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. For measurements of this type, the test waveform is a nominally pure singlefrequency sinusoid and the measure is the summed level of any components produced at harmonics of the chosen frequency. 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 shows the basic principles of each measurement, why it is significant, and how to test and calculate correctly. Ratio measurement procedures are optimistic in up to 7db when evaluating real cochannel distortion. My book distortion explains exactly where harmonic distortion comes from and its not related to intermodulation distortion. Human hearing distortion audibility part 3 audioholics. Audio system measurements are made for several purposes.
1320 153 34 561 810 954 1300 977 476 155 970 1556 1103 605 1544 129 787 1475 1541 1263 1198 1542 1509 53 1220 555 700 1155 1247 134 1007 96 701 994 446 882 1178