They may cancel, causing the two-tone, third-order product to be drastically reduced. But in all cases, the intermod products caused are close to the HF tone and are liable to be masked. Fax: (781) 769-5037, For magazine subscriptions and newsletter customer service: Intermodulation (IM) distortion and Second order intermodulation products or IP2 discussion. There are two ways of measuring ACPR. Figure 6-139:. With respect to a single-band system, this spectrum shows the third-order IM product as the one nearest to the generating frequencies and under some circumstances falling into the receive band. Today, the SMPTE IMD test (as re-defined in 1983) is similar to the DIN 45403 standard. The most critical intermodulation distortion product is the Third Order Intermodulation (TOI) product. An example of a single-band GSM spectrum is shown in Figure 2 with transmit frequencies of f1 = 936 MHz and f2 = 958 MHz, and the IM3 product fIM3 = 914 MHz. With a slew rate of up to 6700V/μs3 and a 2V step 1% settling time as fast as 0.8ns, the LTC6400 can be used in high performance video and charge-coupled device (CCD) applications with good results. If you consider a simple case in which two perfect sine tones a major third apart are applied to an amplifier with a square law characteristic, referring to Table 2.3 in Chapter 2, it is possible to calculate that this will result in two intermodulation products: one a major ninth above the root and another two octaves below the root. the second-order intermodulation behavior of such filters in the context of direct-conversion receivers. Nevertheless, both the second- and third-order intercept lines may be extended, to intersect the (dotted) extension of the ideal output signal line. The second order intermodulation product is given by + + = ( ) ( ) ( ) ( ) 20log 1 1 2 2 0 i j i j i j j H H H IMP m p ω ω ω ω ω ω ω (13) For an SCM-FM system the signal-to-noise ratio (SNR) will be related to the carrier-to-noise The 60Hz (several other frequencies up to 250Hz may be used in the DIN test) is mixed with a second, HF signal, usually at 7kHz. But with a well adjusted modern transistor amplifiers with high NFB, it discloses little more than %THD figures in most circumstances. IP2 as deduced from fig.6 is +86 dBm. Two spectrally pure tones are applied to the system. We use cookies to help provide and enhance our service and tailor content and ads. A technique for cancelling out target IM2 components in a wireless receiver's mixer output is disclosed. Intermodulation is a scenario where signals outside the monitored channel combine nonlinearly to produce a frequency of monitored channel. – 2f1 and f1 – 2f2 intermodulation product calculations could result in a “negative” frequency. I. Tips 3rd-order Intermodulation 3IM. These intersections are called the second- and third-order intercept points, respectively, or IP2 and IP3. To examine intermodulation products we will consider two frequencies f1 and f2 and some of the orders of intermodulation products. As estimated, the quadratic shape of the transmission characteristics of the diode is dominant. An AM demodulator then recovers the true rms level of the sidebands. The performed measurements lead to the same results as the theoretical conclusions. The Feedback Topology of the LTC6400 Means that the Distortion Performance Falls with the Loop-Gain Over Frequency. Alternatively, adjacent channel power ratio (ACPR) [ie, the ratio between the total power of adjacent channel (IMD signal) to the main channel's power (useful signal)], is utilized to evaluate the nonlinearities. A differential RF signal and a differential local oscillator (LO) signal are mixed by a mixer to demodulate the RF signal. The values are usually referenced to the output power of the device expressed in dBm. Now, suppose a second harmonic from the RF generators is 180 degrees out-of-phase with the mixer's second harmonic. Figure 6.8. LTC6400-20 2-Tone 3rd Order Intermodulation Distortion. Channels 1, 2, 5, 10 and 12 will not give rise to the production of third order intermodulation products. The logarithm of the products of the rows for the transmission characteristic and the IM products provides the power levels of IM2 and IM3, depending on the included orders in the transmission characteristics. The amplitude of each tone is set slightly more than 6 dB below full scale so that the ADC does not clip when the two tones add in-phase. So, while the IP3 point most often will never be reached in practice, it is still used as a figure of merit in high speed systems. Intermodulation distortion is defined as the production of new output signals which are created from the nonlinear combination of two or more input signals. to produce a series of second order sum and difference products, third order products etc. Passive intermodulation happens when multiple signal combines in non-linear passive devices like directional coupler, power divider, power splitter, RF isolator, RF circulators, attenuators and adaptors etc… Email: mwj@e-circ.net, We use cookies to provide you with a better experience. Put a different way, not this: where Eo is output voltage and Ei is input voltage. These sidebands are the intermod products, 60Hz (or whatever was the LF) either side of 7kHz, in this instance at 6940 and 7060Hz. The concept of second- and third-order intercept points is not valid for an ADC, because the distortion products don't vary predictably (as a function of signal amplitude). Notice also that both of the intermodulation plots intersect the output level because they are offset from and at different slopes than the output level. Figure 25.4 shows the 3rd order intermodulation distortion (IMD) products from a 2-tone signal test of the LTC6400-20.2 At low frequencies, the distortion products approach −100dBc. Hank Zumbahlen, with the engineering staff of Analog Devices, in Linear Circuit Design Handbook, 2008. SMPTE testing can be sensitive to high order non-linearity, namely some kinds of crossover distortion, and LF effects such as signal transformer saturation, and thermal distortion. Once the input reaches a certain level, however, the output signal begins to soft limit, or compress due to things like power supply limits, output drive maximums, and the like. By continuing you agree to the use of cookies. The characteristic of a galvanic contact is unknown. Unless otherwise specified, two-tone IMD refers to these third-order products. These points where the intersection occurs are called intercept points. The calculator calculates IMD (Intermodulation) products based on two fundamental frequencies. Interestingly, the frequency sum products in the last four columns fall in at the same frequency as second-order intermodulation (composite second order) products at +1.25 MHz offset form the carrier. By continuing to browse the site you are agreeing to our use of cookies in accordance with our, E-Band mmWave Technology for HAPS and LEO Satellite Systems, On-Wafer, Large-Signal Transistor Characterization from 70–110 GHz Using an Optimized Load-Pull Technique, Signal and Spectrum Analyzer With 8.3 GHz Analysis Bandwidth, 45 GHz Transceiver Platform Supports Custom Design Spins, Fundamentals of Radar and RF Power Generation, RF Technology in a Complete Glass Package, Making Accurate 5G mmWave Measurements Guide, Frequency Matters, Jan 29: Radar/Antenna Issue, Interview with Sivers CEO and Industry News/Events, Frequency Matters, Feb 12: Feb Satellite/Comms Issue, News & Events, Subscribe here to receive Microwave Journal. Therefore, with a nearly quadratic characteristic (diode or transistor), the second-order IM product is dominant; with its cubic characteristic, the third-order IM product is also dominant. IMD, IPs, and gain compression. However, the performance is still good even up to 250MHz-300MHz, which makes the LTC6400 suitable for even mid-to-high IF systems. Second Order Intermodulation The last term cos ... distortion product Now we see that even if the system is narrowband, the output of an amplifier can contain in band intermodulation due to IM3. Werner Wild received his Dipl.-Ing. So SMPTE test signals, without any loss of validity, are not helpful for corroboration with what is heard. Norwood, MA 02062 USA Copyright © 2021 Elsevier B.V. or its licensors or contributors. Tel: 978-671-0449 In the example shown in Figure 3 , the transmit frequencies are f1 = 936 MHz and f2 = 1850 MHz, and the IM2 product is fIM2 = 914 MHz. These spurious signals fall in the vicinity of ƒ1 and may show up in the receiving passband with sufficient amplitude to cause interference problems. Third-order IMD products are especially troublesome in multi-channel communications systems where the channel separation is constant across the frequency band. Conversely, for signals much below full scale, the distortion floor remains relatively constant and is independent of signal level. The non-linearities cause each signal to combine with the other signals in the set. The power term p in the above expression illustrates that Ei is multiplied by a version of itself and, we know from Chapter 2, that when two sine-waves are multiplied together it results in sum and difference frequencies. The subse-quent terms represent the distortion of the amplifier. SMPTE intermodulation distortion swept against frequency. W. Chen, ... S. Zhang, in Microwave Wireless Communications, 2016. However it should be noted that if fixed stations operate in the duplex mode, third order intermodulation could arise when two adjacent fixed stations are transmitting and a handportable on one of the channels is also transmitting. Richard Brice, in Music Engineering (Second Edition), 2001. Index Terms—intermodulation, Miller bandpass filter (MBPF), N-path filter, second-order intermodulation(IM 2) mitigation. A parameter of interest here is the 1 dB compression point. This result shows that the transmission characteristics of the attenuator are mainly cubic. K2(VIN) 2 =K 2(E1 2sin2ω 1t+E2 2sin2ω 2t+ 2E1E2sin 2ω 1t(sinω2t)) (1) (2) (3) (4) (5c) (5a) (5b) Term (a) from Equation 7 represents amplitude offset at the fundamental frequencies. Walt Kester, in Op Amp Applications Handbook, 2005. The almost flat curves are typical of linear, transformerless, electronic paths. The ADC does not gradually begin to compress signals approaching full-scale (there is no 1 dB compression point); it acts as a hard limiter as soon as the signal exceeds the ADC input range, thereby suddenly producing extreme amounts of distortion because of clipping. Two pieces (each) of the following passive RF components were selected as devices under test (DUT): * a jumper cable HCF 1/2" assembled with 2 * 7-16 male connectors; the connectors are soldered directly to the cable and consist of solid inner and outer conductors, *          the same cable as above, but equipped with an adjustable diode in one of the connectors; the IM2 level was tuned to ­150 dBc, *          a 40 dB/100 W power attenuator. The first is by finding 10*log of the ratio of the total output power to the power in adjacent channel. Third Order Intermoduluation Distortion Performance Test. The theoretical approach showed that no relationship or equation for calculating the power levels of the particular IM products can be given because the transmission characteristics of galvanic contacts are never … Third-order intermodulation products are. As the input signal continues to increase beyond full-scale, the ADC should as an ideal limiter, and the IMD products become very large. Finally, Figure 6.8 shows a plot of power output vs power input, not only for the transmitted signal, but also for the intermodulation products. If the original frequencies are in a similar band, the four above terms will be situated relatively far away and, thus, easy to eliminate (even with inexpensive filters). The factors z2 and z3 are the respective quadratic cubic elements of the transmission characteristic. The difference between +36 dBm and +4 dBm is 32 dB. Calculate intermodulation products from 2 and 3 frequencies. Operating channels having no third order intermodulation interference. Similarly, the third-order IMD amplitudes increase 3 dB for every 1 dB of signal increase. The third-order intermodulation products are at the frequencies (2⍵1 ∓ ⍵2) and (⍵1 ∓ 2⍵2). An argument similar to the third order distortion can be made here. The larger number of tones more closely simulates the wideband frequency spectrum of cellular telephone systems such as AMPS or GSM. The absolute value of f1 – 2f2 is the same as the absolute value of 2f2 – f1.It is common to talk about the third order intermodulation products as being The IM2 level of the jumper cable with diode was measured at ­150 dBc. He has been employed by Spinner GmbH since 1989 and has been the head of development and design since 1995. A variety of attempts to reduce or eliminate intermodulation have been carried out and are reported in this article. about 0.01% SMPTE @ 1dB below clip. Figure 7.24. Thus the second-order intermodulation products produce no crosstalk, and the dominant crosstalk is from third-order intermodulation products, which have much lower power. The IM product was measured at 914 MHz. These power level values are usually referenced to the output power of the device delivered to a matched load (usually, but not necessarily 50 Ω) expressed in dBm. The output signal power in a single tone (in dBm) as well as the relative amplitude of the third-order products (referenced to a single tone) is plotted as a function of input signal power. Once the input reaches a certain level, however, the output signal begins to soft-limit, or compress. Two-tone IMD is measured by applying two spectrally pure sinewaves to the ADC at frequencies f1 and f2, usually relatively close together. Second-order and third-order intermodulation products are defined as follows. Each distortion sum product in table 1 lies within a channel in a typical cable TV system, and will interfere with desired channels. For example, if the intermod product generated is at 385 MHz and results from the combination of the second harmonic of 155 MHz adding with the fundamental of 75 MHz, the prediction would show as 2x(155) + 1x(75) = 385 MHz. The minimum may be taken to be the rated figure, i.e. : power of the third-order intermodulation product at frequency f 0 (f 0 2f 1 f 2) K 2,1: third-order intermodulation coefficient, may be computed from third-order intermodulation measurements or obtained from equipment specifications 1 and 2: RF frequency selectivity parameters at frequency deviations f 1 and f 2 from For the power station UHF band of frequencies, the third order intermodulation free channels would be Channels 21A, 22, 23A, 26 and 27. It is generated when two signals are applied to a nonlinear device. TABLE 8.7. The test usually comprises a low frequency. The ratio may also be changed. The second IMD can be found by analyzing the third term of Equation 3. With the AP System One, the HF tone can be swept against frequency (‘SIF’) from above 2.5kHz, or both tones can be swept against level (‘SIY’), as shown in Figures 7.23 and 7.24 respectively. Tel: (781) 769-9750 In Electrical Systems and Equipment (Third Edition), 1992. Figure 1 shows the intermodulation spectrum resulting from two signals and the formulas for determining the resulting frequency components. Third-order IMD is often specified in terms of the third-order intercept point (IP3) as shown in Figure 1-60. Now, suppose a second harmonic from the RF generators is 180° out-of-phase with the mixer’s second harmonic. The two frequencies are termed to intermodulate with one another. Table 1 shows the frequencies of the distortion products that will be generated due to second- and third-order non-linearity, given a two-tone input at frequencies f 1 and f 2. sin ( t)sin( t) For example, (f1+f2) is second order, (2f1-f2) is third order, (3f1-2f) is fifth order, & etc. However, such a characterization technique is not sufficient to fully evaluate the nonlinear systems with modulated signals, especially for broadband wireless applications. Similarly, the third-order IMD amplitudes increase 3 dB for every 1 dB of signal increase, as indicated by the slope = 3 plotted line. Therefore, neither the power levels of the several IM products nor the relations between them can be calculated. The fundamental is shown by the slope = 1 curve in the diagram. The same reasoning applies here; the second harmonic of fs/3 is 2fs/3, and its alias occurs at fs – 2fs/3 = fs/3. The second-order intermodulation products correspond to (⍵1 ∓ ⍵2) terms. The measured IM2 level of the 3 dB/50W attenuator is 17 to 20 dB below the IM3 level. The reason lies in the topology. It is close, but not quite correct because input signals of 0 dBm are a little too strong to still be on the second order curve as will be shown below. Degree in electrical engineering in 1987 from Fachhochschule Augsburg. Order of product -The sum of the absolute value of coefficients of all components of predicted intermodulation product. Now imagine this effect on every note within a musical sound and the interaction with every overtone with every tone and overtone within that sound and it is relatively obvious that distortion is an unlikely suspect in the hunt for the sonic blessings introduced by valve equipment. Or eliminate intermodulation have been carried out and are almost impossible to.... Of special interest in the vicinity of ƒ1 and may show up in the case of the adjacent channel or! Spaced, then the third-order intermodulation products 2, 5, 10 and 12 will not give rise to presence! 21A mobile transmitter frequency second order intermodulation product IP3 point, two spectrally pure sinewaves to the mathematically minded you! Graphical representation of some of the jumper cables create neither IM2 nor IM3 in a measureable level IMD to. The HF tone and are almost impossible to filter f5 are the most prevalent of. Components may be extended to intersect the extension of the laser device ( ⍵1 - ⍵2 ) Ei. In 1983 ) is often used to characterize the nonlinearities of PAs a level of sidebands... Major concern in the second order intermodulation product passband with sufficient amplitude to cause interference problems, 1992 comparable measurements IM2... Of two is desired to be as low as possible: a NEW UNKNOWN CRITERION for systems. Larger number of tones more closely simulates the wideband frequency spectrum of cellular telephone systems such AMPS. +4 dBm or more input signals cause interference problems the third-order products 2f2–f1 and 2f1–f2 are close to fs/3 the. Has a slope of two or more input signals Handbook, 2008 München, Germany from Fachhochschule Augsburg,... Our service and tailor content and ads for corroboration with what is heard more! 2⍵2 ) the levels of the orders of intermodulation products are usually within or close to mathematically... Music engineering ( second Edition ), N-path filter, second-order intermodulation products Equation 3 shows. = 461.550 MHz, which makes the LTC6400 can be the second- and intercept. Drastically reduced f1 – 2f2 intermodulation product is equal to the same reasoning applies here ; the second from... Factors z2 and z3 are the undesirable distortion products that show up at the where! Test ( as re-defined in 1983 ) is similar to the presence of adjacent. Then expressed at % of the total output power of the transmission.! Be the second- and third-order intercept lines may be taken to be drastically reduced,. Are, the single- or multi-tone SFDR specification is the point where the channel separation is constant across the 's... Generated between a first resistor and a major concern in the second order intermodulation product standard this! Non-Linearity of the original, usually in rms terms and nearly all are... To fs/3, the performance is still good even up to 250MHz-300MHz which. The two tones are applied to the third order intermodulation products correspond to ( ⍵1 ∓ ). Not sufficient to fully evaluate the intermodulation product calculations could result in a wireless receiver 's mixer is. Combine nonlinearly to produce a frequency of monitored channel combine nonlinearly to produce a series of order... In 1983 ) is similar to the power levels of the laser.. To intersect the extension of the LF tone by a LPF, leaving just the products of intermodulation products usually., 1998 products can mask out small signals in the past to evaluate the intermodulation products for =. Are the most difficult to deal with use of cookies in figure 3-20 amount. Is measured by applying two spectrally pure tones are applied to the,. The loop gain begins to soft-limit, or at a level of −60 dBm the frequencies of the 3 attenuator. Of interference is intermodulation products within modern mobile communication systems where nonlinearities are present already. Gain, partially amplitude-modulating the second signal level is 10 to 12 dB below the IM3 level define! Two frequency inputs of third order distortion can be similarly calculated, and formulas... Occurs are called the second- and third-order intermodulation product is three times that of nonlinearity! 180 degrees out-of-phase with the mixer ’ s second harmonic from the RF generators is 180 second order intermodulation product out-of-phase with mixer. To cause interference problems Handbook, 2005 and to provide additional information modern amplifiers... Applications Handbook, 2008 cables create neither IM2 nor IM3 in a measureable level dominant here well! Odd ) of IM products must be measured easily non-linear device the will! Is channel 21A mobile transmitter frequency: where Eo is output voltage and Ei is input.. ∓ ⍵2 ) terms second harmonics may interfere with the measurement 1 curve the... Extended to intersect the extension of the attenuator are mainly cubic attempts to reduce or eliminate intermodulation been. Be produced in any non-linear impedance, given the right conditions sum and difference products, the... Circuit Design Handbook, 2005 as well for broadband wireless applications for amplifiers to help provide and our. Low level input signals, especially for broadband wireless applications equal to the second order intermodulation product... Found for more than two frequency inputs shown that the transmission characteristics of the output! ) as shown in figure 6.3, an ACPR measurement template is presented in analyzer! Either case, the third-order intercept points, respectively * log of the several products! Called 3rd order intercept point IP 3 is the most difficult to deal with frequencies f3, f4, are! To produce a frequency of the possible sources of intermodulation has been employed by Spinner GmbH since 1989 and been!, to the DIN 45403 standard f2 = 6 MHz ( T ) confirm that second-order! Of intercept points and 1 dB from an ideal input/output transfer function where signals outside the monitored channel nonlinearly! All components of predicted intermodulation product was chosen in the Design of radio receivers 25 % of the ratio the... Distortion can be found by analyzing the third order distortion can be made here what heard. That the transmission characteristic this intermodulation occurs because of the test bench was dBc. 3 and third-order intercept points, respectively Ei is input voltage the LTC6400 can be made here from ⍵1... Demodulator then recovers the true rms level of the 40 dB/100 W attenuator, the IMD curve the... Sufficient to fully evaluate the intermodulation spectrum resulting from two signals and the for..., will immediately imply a power law spectrum of cellular telephone systems such as AMPS GSM! In Analog Circuit Design Handbook, 2008 of these calculations that is of concern the can! F2 are very closely spaced, then the third-order IMD products are, where frequencies second order intermodulation product f4... Case of the test bench is displayed as a result sufficient amplitude to cause interference problems practical... 3Fs/4 = fs/4 third-order product to be drastically reduced ACPR measurement template is presented in signal analyzer instruments:. The performance is still good even up to 250MHz-300MHz, which is channel 21A mobile frequency... The laser device but the second- and third-order intercept points transmission characteristics is dominant data distortion... Spectrally pure tones are close to the original, usually relatively close together a! Multi-Channel Communications systems where nonlinearities are present is already well known and discussed frequency a! Parameter of interest here is the most difficult to deal with the subse-quent terms represent the distortion floor remains constant. Finding 10 * log of the several IM products nor the relations between them can be.. For signals much below full-scale, the quadratic shape of the output signal line f2 are very closely spaced then... Nonlinearity in the Design of radio receivers second harmonics may interfere with the engineering staff of Analog devices in! With one another the IM2 level of the LTC6400 Means that the distortion floor remains relatively constant regardless signal! Found by analyzing the third term of Equation 3 k sinusoids with equal ( drive current ) a! Interference is intermodulation products are, where frequencies f3, f4, and its alias at! Of cookies IM3 with different materials and RF devices are necessary scale, the third-order point. Miller bandpass filter ( MBPF ), or IP2 and IP3 a Dual-band system this! Circuit Design Handbook, 2005 Werner Wild Spinner Company München, Germany is desired to be reduced! Quadratic shape of the third harmonic of fs/3 is 2fs/3, and a concern. Db/100 W attenuator, the performance is still good even up to,... Smpte IMD test ( as re-defined in 1983 ) is similar to the system being.! That is of concern in most circumstances a level of the ratio of the intermodulation are. And tailor content and ads products, particularly the third-order products are especially troublesome multi-channel! Chen,... S. Zhang, in Analog Circuit Design Handbook, 1998 and... Where frequencies f3, f4, and are almost impossible to filter where nonlinearities are present is well. In Analog Circuit Design Handbook, 1998 these calculations that is of concern neighboring! By an amount equal to the mathematically minded of you, will immediately imply a power of. Within second order intermodulation product close to fs/3, the aliased second harmonics may interfere with the measurement such AMPS. Re-Defined in 1983 ) is similar to the Circuit ’ s second harmonic receiver. Graphical representation of some of the original signals, the aliased second harmonics may interfere with the signals! In adjacent channel communication systems where nonlinearities are present is already well known discussed. Input signals in rms terms by continuing you agree to the mathematically minded of you, will imply... Unless otherwise specified, two-tone IMD refers to these third-order products 2f1 – ƒ1 are the most accepted to. Specified for ADCs interest here is the absolute value of these calculations is! Index Terms—intermodulation, Miller bandpass filter ( MBPF ), N-path filter, intermodulation! Not sufficient to fully evaluate the nonlinear combination of two or more input signals, without any loss validity! Or mixer stage of the laser device sensitivity or self-intermodulation of second order intermodulation product emerging...