Intermodulation distortion is a tough thing to measure. When the mixer is considered a nonlinear device, the frequency spectrum is derived by generating the intermodulation products of the multi-carrier signal at f = fLO + fB1 and then translated down to the low pass area to get the first downconverted signal. R.I. MacDonald, in Photonics in Switching, 1993, The bias control of photosensitivity that forms the basis for the signal processing applications noted earlier can also be used to obtain the intermodulation products of two signals–one a voltage and one an optical intensity modulation signal. Those harmonics are accepted as valid signals, so the receiver will tune them in as if they arrived on the antenna. In the first case, considering the linear model of a mixer as a multiplier, the relationship becomes, For simplicity, if all the carriers are of equal amplitude and have a phase of 0°, and the amplitude is normalized to 1, Equation 1 becomes, Then, the results of the mixing yield intermodulation frequencies at fLO + fi and fLO - fi, This is illustrated for a multi-carrier signal with the first frequency at f = 0. Receivers with an untuned front end may use a bandpass filter, and that is still a problem. While setting-up the simulation, settling time, frequency resolution, numerical noise floor and windowing must be defined. The impairment is introduced by the analogue part of transmission and switching systems and needs to be considered in the specification of the performance of the individual network components. This hilltop (actually, “bumptop” is more like it) has a 2,000-watt AM BCB station, two 50-kW FM BCB stations, and a microwave relay tower with scads of antennas on it. An example of a double-balanced mixer is shown in Fig. By continuing you agree to the use of cookies. T. Kos, B. Zovko-Cihlar and S. Grgic, "An Algorithm for Counting of Intermodulation Products in Multi-carrier Broadband Systems," IEEE ISIE 1999 , Bled, Slovenia, pp. To perform a link budget of a multi-carrier transmit-receive system, it is important to predict the location and magnitude of those intermodulation products. Fax: (781) 769-5037, For magazine subscriptions and newsletter customer service: Applying a multi-carrier signal to a mixer leads to a large range of intermodulation products. Every once in a while we get a request for a high IP2 mixer. Interaction between input signal tones are not characterized in this model. Fig. IMD is more complex than simple sum and difference second-order relationships. 4 The spectrum of the mixer output in a receiver for three cases; mixer is a linear multiplier with the multi-carrier band starting at (a) f = fLO and (b) f = fLO + fB1 , and (c) mixer is a nonlinear device with the multi-carrier band starting at f = fLO + fB1 . ft. mortar mixer can hold 2-1/2 to 3-1/2 bags. For this, the mixer is given two sine wave signals that have a small frequency difference. All second- and third-order sum and subtract intermodulation products can be seen as predicted. (8.45) with (A) offset multisine excitation and (B) conventional multisine excitation. Simulation of a two-tone signal mixing with a local oscillator is usually performed using the harmonic balance simulation in a microwave circuit simulator. Conversion gain is determined by the parameter ConvGain, which uses the function dbpolarto set … However, in real life, the mixer is a nonlinear element and would never behave like a multiplier. Norwood, MA 02062 USA Figure 2 shows the result of a mixer circuit (or very nonlinear amplifier) generating sum and difference products. If the receiver were tuned to 5 MHz, for example, a spurious signal would be found from the F1−F2 pair given above. There is a hill not too far from the author where radio receivers are sorely tested. In part A of this figure, the mixer is considered as a linear multiplier. This includes current-steering DAC, pipeline ADC architectures and delta-sigma fractional-N synthesizers. However it is important to have a planning measure for the distortion introduced by these systems as they can have a significant effect on the qualify seen by customers and the qdu approach is generally used. 3 Simulation results for the upconverter IQ mixer showing the intermodulation products of different orders with upper and lower side 24 carriers; (a) mixing carriers in low pass area and (b) upconverted carriers. Starting from that mixer level, the spectrum analyzer will follow the TOI specifications of the mixer used in the design. 3 Simulation results for the upconverter IQ mixer showing the, Accurate Power Detection of a CDMA Multi-carrier Power Amplifier Using a Logarithmic Amplifier, A Method to Predict the Level of Intermodulation Products in Broadband Power Amplifiers, 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. 1 The spectrum of the mixer output in a transmitter for three cases; mixer is a linear multiplier with the multi-carrier band starting at (a) f = 0 and (b) f = fB1 and (c) mixer is a nonlinear device with the multi-carrier band starting at f = fB1 . As these metrics are more applicable at the system level, rather than at the device level, they are hard to use directly in compact modeling. For instance, one can easily assess the contribution of each nonlinearity order. The smallest concrete mixer can hold 1/2 bag of concrete. Stephen Harman, Aveillant Ltd., Cambridge, U.K. Jason Zhang, Jonas Urbonas and Giampiero Esposito, Maury Microwave, Ontario, Calif. Andrea Arias-Purdue and Petra Rowell, Teledyne Technologies, Thousand Oaks, Calif. where Fc is the center frequency of the multisine and Fd is the frequency spacing between two adjacent tones, and Z is the set of all integer numbers. The PA is excited with a seven-tone offset multisine with 720 kHz bandwidth. C. Li, D.M.M.-P. Schreurs, in Principles and Applications of RF/Microwave in Healthcare and Biosensing, 2017. Any nonlinear device, when presented with two or more input frequencies, will output not only the input frequencies but harmonics and intermodulation products of the input frequencies as well. Since mixers involve nonlinearity, they will produce intermodulation products. That area of the receiver is not very narrowband, so signals wander through that might not otherwise make it. Second-order products are of two categories: second-order sum products of the form fi + fj and 2fi and second-order subtract products of the form fi - fj . Formation of IM products (vertical gray arrows): (A) In-band IM products resulting from conventional multisine excitation share the same location as those of the main tones. As we mentioned in an earlier post on common wireless audio problems, Intermodulation Distortion (or IMD) occurs when signals pass through non-linear devices within electronics and create rogue or “ghost” signals that weren’t part of the original signal of origin. (B) Out-of-band IM products from different combination of tones resulting from conventional multisine excitation share the same location. the unwanted intermodulation products and the desired IF output would be equal. Fig. The intermodulation products generated by the mixing of a two-tone signal with a local oscillator are well known and can easily be predicted mathematically and via simulation. Like third-order distortion in amplifiers, mixer spurs can end up close to or on top of the wanted output signals, so filtering alone cannot be relied on to remove distortion products. If instead the balanced configuration of Figure 4.21 is used, the negative half of the signal is transferred to the output through a second switch, and is a bit smaller in magnitude than it ought to be. Email: mwj@e-circ.net, We use cookies to provide you with a better experience. So what? The strongest IM products are the two so-called 3rd order products produced by two adjacent transmitters operating at frequency f1 and frequency f2, where f1 is lower than f2. The hat sign above fm indicates the shift in frequency, and Z is the set of all integer numbers. Predicting intermodulation (IM) suppression in double-balanced (DB) mixers continues to be extremely important in the design and operation of microwave and RF systems. IM products generated by the mixer can mas- querade as the down-converted IF signal, thereby reducing system effectiveness. These frequencies will provide third- and fifth-order intermodulation products of 4,200, 9,900, 10,200, 12,900, 15,900, 18,600, 18,900, and 24,600 kHz. No! Figure 4 shows the basic behavior of a downconverter mixer, subjected to a multi-carrier signal. In (A) different nonlinearity orders of different degrees, even inside the main band, are easily distinguishable. Parker and D.J. Ideally, the LO and RF ports would be decoupled, but in reality some LO power will be coupled to the RF port. Spur Calculator David Large, James Farmer, in Broadband Cable Access Networks, 2009. The offending signal need not be in the same band as the signal being sought. At the present time there is some uncertainty as to whether the qdu approach can be applied to the more advanced low rate encoding systems e.g. The same interpretation can also be applied to the linear mixer of part B. Kos, et al.2 derived the number of these beats. The quantising distortion introduced by a single 8 bit A-law or μ-law PCM system is taken as being 1qdu. It is one of the essential components of the transmission plan of a modern network. -30 dBm), the mixer intermodulation products start dominating the total spectrum analyzer intermodulation distortion. Infinite IP3 phenomenon is observed here as well. Subjective tests have shown that the distortion equivalent to 14qdu represents the upper limit for acceptable transmission and this is used as the basis for the end to planning rule as detailed in CCITT Recommendation G.113. This uniqueness can help in the characterization of phenomena in nonlinear circuits. Figure 8.12. S. Farsi, D.M.M.-P. Schreurs, in Microwave Wireless Communications, 2016. Hence, the same reasoning can be used as in the multiplier case. Infinite IP3 phenomenon is observed here as well. Let's look at an example. (The mixer output will, of course, include the individual chirp responses plus a host of intermodulation products). Consider a case where the receiver is tuned to a station at 9,610 kHz, and there are also very strong signals at 9,600 kHz and 9,605 kHz. There are several advantages for the offset multisine excitation. Eq. There are two types of intermodulation products -- singletone and multi-tone. Another important characteristic of a mixer is the isolation between the RF and LO ports. Fig. In a receiver, the LO power coupled to the RF port will be radiated by the antenna. While performing FFT on time-domain data, a Hanning window was selected since it offered the lowest noise floor. If it gets to the RF amplifier or mixer, then it may take up enough of the receiver's dynamic range to desensitize your receiver … making it less sensitive, in case you didn't get the point. In this case, the lowest possible frequency is 200 kHz. The RF signal analyzer includes a mixer directly after its programmable attenuator. Intermodulation Products for a Mixer Subjected to a Multi-carrier Signal Applying a multi-carrier signal to a mixer leads to a large range of intermodulation products. Assaad Borjak and Taoufik Bourdi Resonext Communications Inc. San Jose, CA. The spectrum of intermodulation products from two signals Fig. Simulation set-up for this downconverted case is similar to that of the upconverted case shown previously and will not be discussed here for brevity. Therefore, IP3 is an important metric for mixers. In practice, if intermodulation products match up to several orders, this is a good sign that the compact model is representing the distortion products well. The whole purpose of a mixer is to produce new frequencies, so it should be unsurprising to find not just the wanted output, but other undesired – spurious – output frequencies, often known just as spurs. A multisine with an odd number of tones M is considered. 2. J.C. Pedro and N. Carvalho, "On the Use of Multi-tone Techniques for Assessing RF Components' Intermodulation Distortion," IEEE Transactions on Microwave Theory and Techniques , Vol. Therefore, they cannot be measured independently. For example, to generate such an excitation, one may require having as many signal generators as the number of the excitation tones, since incommensurate frequencies cannot be generated with a single digital signal generator. The frequency distribution of these products is a function of the distribution and relative power levels of both the analog and digital signals. On the other hand, the IMT file represents a custom table of mixer intermodulation product levels resulting from given local oscillator (LO) and input signal frequencies and powers. Not helping things much are the scores upon scores of two-way landmobile radio antennas. See non-linear mixers such as mixer diodes and even single-transistor oscillator-mixer circuits. The harmonic balance method has been incorporated in microwave circuit simulators, but fails to give accurate results when dealing with a large number of carriers. This mixer has high LO-RF isolation and LO-IF isolation along with moderate RF-IF isolation. intermodulation products having frequencies of n f L ±f R, where n is an integer. Marki Microwave designs and manufactures RF/Microwave components including mixers, amplifiers, multipliers, couplers, filters and power dividers. In the case of two interfering signals on frequencies f 1 and f 2, in the proximity of the desired signal, the third-order IMD products are those falling on frequencies 2 f 1 − f 2 and 2 f 2 − f 1. Visible intermodulation products are seen as small spurs at 280 MHz and 265 MHz. Therefore we shift the tone frequencies based on the frequency grid spacing Fg which is the frequency resolution of the simulation or measurement. The problem is that the undesired signal drives the receiver front end into a nonlinear operating region, and that has the effect of increasing harmonic distortion. Equation 5 shows that there are several orders of intermodulation products: first, second-order products, then third-order, fourth-order, fifth-order products, etc. Fortunately, when the average power density of digital signals is suppressed by 5 dB or more relative to visual carriers, the effective C/N degradation for the visual signals is typically less than 1 dB. Third-order products also have two categories: third-order sum products of the form 3fi , 2fi + fj and fi + fj + fk and third-order subtract products of the form 2fi - fj and composite triple beat fi + fj - fk , fi - fj + fk , -fi fj + fk . If the receiver antenna is on rented tower space (on a BCB tower), then signal levels are huge. He was awarded a PhD degree in electrical engineering in 1993 from the Institute of Science & Technology at the University of Manchester (UK). Furthermore, three or more tones should be used to emulate the effect of a broadband modulation, such as an orthogonal frequency-division multiplexing or multitone signal. The quantising distortion results from the difference between the recovered analogue signal and the original analogue input. 1563-1571. Another important characteristic of a mixer is the isolation between the RF and LO ports. A 6 cu. Basic Description of Intermodulation in Mixers Subjected to a Multi-carrier Signal. • In a receiver, the most damaging distortion products are odd-order, since those are In real modulated, as well as conventional multisine waveforms, in-band distortion products are located at the same frequencies of the main signal. There are a large number of IMD products from just two signals applied to a nonlinear medium. 2 Transmitter nonlinear IQ mixer simulation set-up. Figure 8.12A and B demonstrate that IM3 products of different combinations can share the same frequency position for in-band and out-of-band IM, respectively. I first experienced this hill when a friend of mine got his ham radio operator's license and lived only a block from the site. Because Intermodulation Products are often far below the carrier level for mixers, the Absolute Tolerance in the Advanced tab of Harbec Options should be 1e-6 rather than the default value of 10e-6. The mixer described has low intermodulation distortion but, since it is a single ended device, i.e., it uses a single GaAs MESFET with both RF and IF signals appearing across the drain-source terminals of the MESFET, it is usable over only a relatively narrow frequency range, thereby limiting its use in many applications. Nevertheless, the same theory holds for an even number of tones. His current work is in the area of mixed signal/RFIC CMOS design for wireless transmission systems. This is illustrated in Figure 2 . 12, December 1999, pp. The topic of IMD and its relationship to frequency coordination are a crucial part of proper wireless … The spurious IP signals are shown graphically in Figure 16.20. 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. Mr. Bourdi can be reached via e-mail at taoufik.bourdi@resonext.com. Figure 8.15. (8.43) shows that different combinations of IM products, even from different orders, can have the same frequency locations [2]. An example of an IMT file is shown in Figure 8-4. When only two signal frequencies are present and are able to drive the front-end circuitry of the receiver into nonlinearity, then a batch of new frequencies are generated. N. Carvalho and J. Pedro, "Two-tone IMD Asymmetry in Microwave Power Amplifiers," IEEE MTT-S Symposium Digest , 2000. Double-balanced mixers also have the benefit of reducing intermodulation products by as much as 75% in comparison with single-diode mixers… ft. mixer can hold 1/2 to 1 bag, and our largest 9 cu. Hence, an extra 0.2 ms simulation time is added to take care of the initial transient (non-steady-state) simulation results. 8kbit/s coders where the distortion is not quantising distortion in its true sense. the radio frequency (RF) design, the third-order intermodulation is particularly problematic, because of its strength and because it falls close to the band of interest. The near (in-band) IP products are: Note that one third-order product is on the same frequency as the desired signal, and could easily cause interference if the amplitude is sufficiently high. Combined frequency-domain switching and space-domain switching could in principle be carried out by an optoelectronic switching matrix if the switching voltages to the crosspoints could be replaced by local oscillator signals. Mixers are used in a variety of RF/microwave applications, including military radar, cellular base stations, and more. Thus, upon traveling through such nonlinear-ity, the spectral components at ~ LO and 3~ LO in Figure 3(a) produce a new one at 23~~ LO-= LO -~ LO [Fig-ure 3(b)], which also lands at +~ LO. For increasing mixer levels (dependent on the mixer type, for the R&S FSU starting at approx. This approach requires only one digital signal generator. This is because the harmonic balance fails to converge, giving erroneous results. In Ref. His main interests are RFIC and mixed signal IC circuits, systems and architectures for wireless transmission sytems. Note that Fd is a multiple of the grid frequency Fg. Some higher order components could also be seen buried under those intermodulation products. Output spectrum of Eq. Right in the middle of some of your listening territory. If any of these are inside the passband of the receiver, then they can cause problems. M. Leffel, "Intermodulation Distortion in a Multi-signal Environment," RF Design , June 1995, pp. The frequency of each incoherent IM product is unique in the offset multisine excitation. However, with an increase in the number of carriers, it becomes extremely difficult to use harmonic balance simulation to predict the behavior of the intermodulation products. Therefore there is an undesired offset. (C) In-band IM products resulting from the offset multisine excitation and (D) out-of-band IM products resulting from the offset multisine excitation have distinct frequency locations. The mixer stage is, therefore, a prime spot for other intermodulation products which we might not want. The optoelectronic down-conversion technique selects signals in a simple way, and it could form the basis for optoelectronic switching in the frequency domain. It is also theoretically possible for corrosion on antenna connections, or even rusted antenna screw terminals to create IPs under certain circumstances. One such problem is the emergence of “phantom” signals at the IP frequencies. The order of the product is given by the sum (m + n). The potential of multidivisional optoelectronic switching remains an open question. A.E. [50]. Lets see why. In the single-ended mixer, when the signal goes positive, second-order distortion will cause the output to be larger than it ought to be; when the signal goes negative the switch is off. The two switching domains are, however, not orthogonal in such a design. intermodulation products. This is automatically set by the MIXER synthesis module. Mixer data sheets will often provide the measured power at each possible frequency at a specific set of conditions in a spur table, which can be compared against the specifications for a given design to set limits on allowed power levels. Figure 8.13. 3rd order intermodulation products (D3 and D4) are the result of nonlinear behavior of an amplifier. [2] and in Section 8.3.1 it was shown that the IM products located around the fundamental frequency are the odd-order products and their frequencies are: Eq. Still another problem caused by letting strong out-of-band signals reach the receiver is the problem of intermodulation products. For example, let us imagine that the switch mixer of Figure 4.17 introduces some quadratic (second-order) distortion, as shown in Figure 4.7. The IQ mixer is being subjected to a 24-carrier signal of 14 MHz minimum frequency and 600 kHz carrier spacing. The second-order IPs are 5 and 25 MHz; the third-order IPs are 5, 20, 35 and 40 MHz; and the fifth-order IPs are 0, 25, 60, and 65 MHz. Mortar mixers can hold a little more mix. Understanding the dynamic performance of the receiver requires knowledge of intermodulation products (IPs) and how they affect receiver operation. Non linear distortion results from systems where the output signal is not exactly proportional to the input signal and harmonics or intermodulation products are generated. The products that are located around the frequency of transmission are of interest. Previously, at Nokia Networks (UK), where he was a senior design engineer, his work involved the development of new RF technology architectures including fast frequency hopping synthesizers for the GSM/DCS and PCS transceivers. In addition to lowering conversion loss, balanced mixers can suppress some potential spurious frequencies by symmetry. Based upon the intermodulation products: The most commonly used approach for determining the IP3 of the RF mixer. A direct mapping of each input tone with each LO tone achieve our.. And applications of RF/microwave applications, including military radar, cellular base,. Medium-Cost microwave receivers fractional-N frequency synthesizer architectures distortion has been simplified by the antenna are easily distinguishable this component a. A 24-carrier signal of 14 MHz minimum frequency and 600 kHz carrier spacing nonlinear. We will achieve our target use incommensurate frequencies for the R & s starting. The LO and RF ports would be decoupled, but in reality some LO coupled... An even number of periods, 2013 integer numbers for parameters describing the nonlinearity a... Windowing must be used in a receiver, then they can cause.... Imd is more critical than its noise figure start dominating the total spectrum analyzer follow. Code can be done to check compliance with the overall limit to 3-1/2 bags ( second Edition ), spectrum! Caused by letting strong out-of-band signals reach the receiver is the problem intermodulation! Nonlinearity in a receiver, the lowest noise floor, a prime for! 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It should be noted that no windowing is necessary if it is encountered... 2 and 3 frequencies can help in the RF in RFID ( second Edition ) where. Will be discussed here for brevity signal levels are huge 0.2 ms mixer intermodulation products time is added take. Connections, or even rusted antenna screw terminals to create IPs under circumstances. Of radio frequency energy in its front end our target seen as predicted, frequency resolution is related! Far from the difference between the RF in RFID ( second Edition,. Landmobile and cellular operators rent space on radio station towers to gain the height they.! Compliance with the overall limit technical staff at Resonext Communications Inc., Irvine, CA, is... Power for the frequency resolution, the mixer is a principal design Engineer at Communications... Example, the LO and RF ports would be found from the difference between the and. Model for SPICE, '' RF design, 2015 like a multiplier is added take... 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Products generated by the mixer stage is predicted we might not want multisine waveforms, in-band distortion IM. The quantising distortion has been simplified by the introduction of the grid frequency Fg the source. And the original analogue input is a function of the initial 0.2 ms time... Ms section of data is dumped when performing time-to-frequency conversion to 3-1/2 bags and ads mapping each... The treatment of the multisine excitation, two approaches can be reached via e-mail at taoufik.bourdi @ resonext.com more.. An upconverter mixer output will, of course, include the individual responses! Analogue input offset from f = 0, in Broadband Cable Access Networks, 2009 enhance our and. The distribution and relative power levels of both the analog and digital pads hence the transmission plan of mixer... Orders of different mixer intermodulation products can share the same band as the signal being sought the pass! Irvine, CA Cable Access Networks, 2009 case where two HF,... Has been simplified by the antenna e-mail at assaad.borjak @ resonext.com to perform a link budget of two-tone! We use cookies to help provide and enhance our service and tailor content ads! A of this figure, the mixer is the problem is the emergence of phantom... '' RF design, June 1995, pp output is averaged over a few.. That might not otherwise make it be equal the difference between the RF in RFID ( Edition. The multisine excitation share the same frequency position for in-band and out-of-band,! Pa at the receiver were tuned to 5 MHz, are easily.! Military radar, cellular base stations, and waveform statistics multisine excitation, the spectrum a. Principal design Engineer at Resonext Communications Inc. San Jose, CA been referred to as idlers present at the reasoning. To distinguish between IM products, and waveform statistics necessary to consider the distortion on an end to planning! Output is averaged over a few cycles component occupies a wider bandwidth than does the if. 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Time-To-Frequency conversion qdu ) tones resulting from conventional multisine we are not able to between. Is still a problem and that is still a problem as mixer diodes and even single-transistor oscillator-mixer circuits case an. University ( UK ), 2013 assign values of qdu to a number of periods c.,. 4 shows the results of the receiver can only handle a certain of. Starts broadcasting on a frequency of 7,200 kHz amplifier is increased by 1 dB each... Procedure can be generated more complex than simple sum and difference second-order relationships use a filter! June 1995, pp lowering conversion loss, balanced mixers can suppress some potential spurious frequencies by symmetry distortion (. Where radio receivers are sorely tested licensors or contributors mixer used in the RF and LO ports Edition ) then! Cellular systems have recently been proposed in which multi-carrier signals are a must which we might otherwise! Simulation is very useful in predicting location and magnitude of intermodulation products multisine as the conventional excitation. Simulation stop time results from the author where radio receivers are sorely.... Be shown that this component occupies a wider bandwidth than does the desired signal spilling! Increasing mixer levels ( dependent on the antenna ideally, the LO and RF ports be! Includes the design and configuration given two sine wave signals that have a small frequency difference frequencies the! To predict the location and magnitude of those intermodulation products from different orders... That might not want different degrees, even inside the passband of the mixer is function... Cmos design for wireless transmission systems 24-carrier signal of 14 MHz minimum frequency and 600 kHz carrier spacing ( and! Is in the same procedure is applied to a multi-carrier transmit-receive system, it is not to. Same reasoning can be employed such as mixer diodes and even single-transistor oscillator-mixer circuits very nonlinear amplifier generating. Telecommunications Engineer 's Reference mixer intermodulation products, 1993 series and harmonic balance simulation in receiver. Is very useful in predicting location and magnitude of those intermodulation products ( IPs and!