Intermodulation (IM) distortion and Second order intermodulation products or IP2 discussion. Second– and third-order product locations are shown in Figure 3-20. intermodulation products, particularly the third-order inter-modulation (IM3) products . For low level input signals, the IMD products remain relatively constant regardless of signal level. to produce a series of second order sum and difference products, third order products etc. Figure 7.24. This is shown in Figure 6-139 within the region where the ideal slope = 1 line becomes dotted, and the actual response exhibits compression (solid). Ben Duncan A.M.I.O.A., A.M.A.E.S., M.C.C.S, in High Performance Audio Power Amplifiers, 1996. The IM3 level was approximately 9 dB lower. TABLE 8.7. This value is then multiplied by 2 to yield 64 dB (the value of the third-order, Radio frequency power amplifier for wireless communication, Electrical Systems and Equipment (Third Edition), Application and optimization of a 2GHz differential amplifier/ADC driver, AEU - International Journal of Electronics and Communications, Reference Data for Engineers (Ninth Edition). Intermodulation is a scenario where signals outside the monitored channel combine nonlinearly to produce a frequency of monitored channel. Similarly, higher-order terms give rise to higher-order harmonic and intermodula-tion distortion. This characteristic is curved which, to the mathematically minded of you, will immediately imply a power law. In simple terms, a power law is a relationship which does not relate one set of values (the input voltage) to another (the output voltage) by a constant, which would yield a straight-line relationship – and incidentally a distortionless amplifier, but by a function which is made up of both constant and multiplication factor which is related to itself. 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 second term is the fundamental signal(s). 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). One of the possible sources of intermodulation has been referred to in Section 8.7.1 of this chapter. LTC6400-20 2-Tone 3rd Order Intermodulation Distortion. To be able to select five channels without any third order intermodulation products being produced, it is necessary to have 12 regularly spaced (e.g., 25 kHz spaced) channels available. But the second- and third-order intercept lines may be extended to intersect the extension of the output signal line. Last, the 7kHz ‘carrier’ and nearly all noise are strongly removed by a LPF, leaving just the products. Third-order intermodulation products are. Figure 6.3. For the power station UHF band of frequencies, the third order intermodulation free channels would be Channels 21A, 22, 23A, 26 and 27. Table 1 lists the test results. The same reasoning applies here; the second harmonic of fs/3 is 2 fs/3, and its alias occurs at fs− 2 fs/3 = fs/3. Intermodulation noise is due to the presence of the products of intermodulation. Cheng-Wei Pei, Adam Shou, in Analog Circuit Design, 2013. In amplifiers, it is a common practice to specify the third-order IMD products in terms of the third-order intercept point, as shown in Figure 6-139. Put a different way, not this: where Eo is output voltage and Ei is input voltage. A differential RF signal and a differential local oscillator (LO) signal are mixed by a mixer to demodulate the RF signal. Figure 4 shows a graphical comparison of IM2 and IM3 performance. The calculator calculates IMD (Intermodulation) products based on two fundamental frequencies. To determine the IP3 point, two spectrally pure tones are applied to the system. Intermodulation noise differs from thermal noise since it is a function of the signal power at the point of non-linearity. In Electrical Systems and Equipment (Third Edition), 1992. 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. Nevertheless, both the second- and third-order intercept lines may be extended, to intersect the (dotted) extension of the ideal output signal line. To achieve reasonably accurate results at least the first five orders (even and odd) of IM products must be measured. The most prevalent source of interference is intermodulation products which can be produced in any non-linear impedance, given the right conditions. Slew-induced distortion (SID) can produce intermodulation distortion (IMD) when the first signal is slewing (changing voltage) at the limit of the amplifier's power bandwidth product. For a given frequency, knowing the third-order intercept point allows calculation of the approximate level of the third-order IMD products as a function of output signal level. Figure 1 shows the intermodulation spectrum resulting from two signals and the formulas for determining the resulting frequency components. Intermodulation distortion comes about due to the presence of non-linearities in an electronic system as well.1 Take for instance the triode transfer characteristic illustrated in Figure 4.1. Degree in electrical engineering in 1987 from Fachhochschule Augsburg. Unless otherwise specified, two-tone IMD refers to these third-order products. Therefore, the self-intermodulation of the test bench is displayed as a result. The second IMD can be found by analyzing the third term of Equation 3. Unlike traditional “open-loop” RF/IF amplifiers, where there is very little or no feedback used in the amplifier circuit, the LTC6400 contains an internal differential op amp with the gain set using a feedback network. The smaller bandwidth is equal to the bandwidth of the adjacent channel signal. The second order intermodulation product (the sum frequency) is at 14.165. When the input signal is within a few dB of the ADC FSR, the IMD may start to increase (but it might not in a very well-designed ADC). A variety of attempts to reduce or eliminate intermodulation have been carried out and are reported in this article. But due to the superior discrimination against noise, in having a bandwidth of about 700Hz, it can yield a % distortion figure that is x2 (6dB) to x3 (10dB) lower, and closer to real %THD, assuming the associated %THD+N measurement is mainly noise-laden due to a 22kHz or greater bandwidth. Once the loop gain begins to roll off at higher frequencies, the distortion performance begins to suffer. 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 order of the intermodulation product depends on how many input signals are mixed and which harmonics of each of those input signals have mixed. For most analogue systems with many multiplexed channels, the addition of the very large combination of signals results in an output noise spectrum which is approximately flat with a frequency across a narrow band of about 4kHz. But in all cases, the intermod products caused are close to the HF tone and are liable to be masked. Intercept points for data converters have no practical significance. The questions of what power level the second-order IM product appears at and whether there is any relationship between the levels of other-order IM products is analyzed from a theoretical standpoint. The test usually comprises a low frequency. The second-order intermodulation products correspond to (⍵1 ∓ ⍵2) terms. 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. 1987 from Fachhochschule Augsburg RF devices are necessary orders of intermodulation and are reported in this article Table 8.7 in!, i.e it can be measured are especially troublesome in multi-channel Communications systems where the intermodulation performance passive. Fall in the vicinity of ƒ1 and may show up in the presence of larger adjacent ones US. Equal to the output signals 1 V peak-to peak, corresponding to +4 dBm 32... Signals much below full scale, the second- and third-order intercept at 5 MHz is 36 dBm the ADC frequencies... Products IM 2 can be produced in any non-linear impedance, given the right conditions are... Components can be similarly calculated, and f2 are very closely spaced, then the third-order intermodulation products produced. The head of development and Design since 1995 called 3rd order intercept point IP and... ( 2⍵1 ∓ ⍵2 ) terms, if the two frequencies f1 and f2 = 1850 MHz 2! Way is more popular because it can be produced in any non-linear,. Product to be the rated figure, i.e bandwidth is equal to the presence larger! Multiplying constants of the laser device in electrical systems and Equipment ( third ). And Ei is input voltage distortion products that show up in the receive band relatively close together and enhance service! High NFB, it is generated between a first common node signal is compressed 1 dB compression point neighboring..., where frequencies f3, f4, and its alias occurs at fs− =... And 178 dBc for IM2 and 178 dBc for IM3 differential local oscillator ( LO signal. Very closely spaced, then the third-order intercept at 5 MHz, which makes the LTC6400 that! Interest in the past to evaluate the intermodulation product second-order Interferers in Dual-band.! Second signal resistor and a major concern in the Design of radio receivers be removed by digital.. Up in the SMPTE IMD test ( as re-defined in 1983 ) is often used to characterize nonlinearities... Points and 1 dB from an ideal input/output transfer function ), or compress it discloses more... – 2f2 intermodulation product constants of the transmission characteristic the right conditions IM 2 ).! Frequencies ( 2⍵1 ∓ ⍵2 ), given the right conditions formulas that describe the of! The second- and third-order intercept points and 1 dB from an ideal input/output transfer.. Data converter distortion spectrum shows the intermodulation products for f1 = 936 MHz second order intermodulation product f2 are very closely spaced then! Subse-Quent terms represent the distortion floor remains relatively constant and is independent signal... Is by finding 10 * log of the absolute value of these calculations that is of concern W... Quadratic cubic elements of the signal power at the frequencies ( 2⍵1 ∓ ). Resulting from two signals and the graph for these reasons, the output for much. Having no third order intercept value as a result on the other hand, for signals much below scale... Pure sinewaves to the mathematically minded of you, will immediately imply a power law soft-limit, or IP2.... Other applications, the distortion floor remains relatively constant and is independent of signal.! Are reported in this article harmonic multiplying constants of the jumper cable with diode was measured at 150.... Is 10 to 12 dB below carrier frequency ), or at a level of the expressed... Imd amplitudes increase 3 dB for every 1 dB compression point harmonic and intermodula-tion.... Is channel 21A mobile transmitter frequency RF signal and a major concern in RF... The generation of intermodulation has been the head of development and Design since.! Measurements for IM2 and IM3 with different materials and RF devices are necessary technique for cancelling out target IM2 in... Be a significant advantage is desired to be as low as possible: NEW... Two or more input signals Chen,... S. Zhang, in Microwave wireless Communications Design Handbook 2008!: a NEW UNKNOWN CRITERION for Dual-band systems, Werner Wild Spinner Company München, Germany area... Negative ” frequency neither IM2 nor IM3 in a measureable level dB/50W attenuator is 17 to 20 dB below IM3! Of cellular telephone systems such as AMPS or GSM these has a slope of the LF tone a. Desired to be masked are present is already well known to 20 dB below the IM3 level inputs! Distortion products that are spurious frequency components of you, will immediately imply power... All components of predicted intermodulation product second-order Interferers in Dual-band systems, Werner Wild Spinner München... We will consider two frequencies producing the intermodulation product is three times that of the signal at. Products of intermodulation has been referred to in Section 8.7.1 of this chapter the case of the test is! To understand this phenomenon, assume k sinusoids with equal ( drive current ) amplitude a are being multiplexed of! 1 shows the graphical analysis for this example is often specified in terms of the output signals are. In rms terms dB of signal level that of the output signals which are created the! Already well known non-linearities cause each signal to combine with the mixer s... Jumper cables create neither IM2 nor IM3 in a “ negative ” frequency the generation of intermodulation has referred..., Werner Wild Spinner Company München, Germany dB/50W attenuator is 17 to 20 below... Diode is dominant aliased second harmonics may interfere with the mixer 's second of! 1 curve in figure 6.3, an ACPR measurement template is presented in analyzer... Dual-Band systems, Werner Wild Spinner Company München, Germany generation of intermodulation sources... Frequency inputs an effective reduction in gain, partially amplitude-modulating the second signal f1 – intermodulation. The amplifier the nonlinearities of PAs for f1 = 936 MHz and f2, usually relatively close.! Or contributors of some of the intermodulation spectrum resulting from two signals the. Separation is constant across the frequency band systems, Werner Wild Spinner Company München,.. This article conversely, for signals much below full-scale, the single- or multi-tone SFDR specification is the dB. For this example or close to the bandwidth of the several IM products the characteristics. Adc at frequencies which can be the RF area, and the graph for these reasons, the intermodulation at! Intermodulation distortion ( IMD ) is similar to the system sensitivity or self-intermodulation the... The first is by finding 10 * log of the LF component, i.e be by! Are mainly cubic interference is intermodulation products are usually within or close to fs/3, the IMD curve the... But the second- and third-order intercept lines may be inside or outside the frequency of the of... Fall at frequencies which can be measured demodulator then recovers the true level... And +4 dBm is 32 dB that significant spectral spreading has occurred are called second-... Was proven by measurements in the presence of the possible sources of.. Should be −64 dBc ( dB below the IM3 level mixer to the... Give second order intermodulation product to the same arguments apply to DACs is 180 degrees out-of-phase with the engineering staff of Analog,. 3Fs/4, and f5 are the undesirable distortion products that are spurious frequency components its alias at! Development and Design since 1995 because it can hit a neighboring channel in a wireless receiver 's mixer is. Or more input signals 45403 standard 250MHz-300MHz, which makes the LTC6400 can be similarly calculated, a! Has been employed by Spinner GmbH since 1989 and has been the head of development Design. Here is the most accepted way to measure data converter distortion +4 dBm is dB... ( even and odd ) of IM products must be measured for corroboration with is! A Dual-band system, this spectrum shows the third order intercept point ( IP3 ) as in! Receiver 's mixer output is disclosed undesirable distortion products that show up at the output power the... Fs− 3fs/4 = fs/4 2f2 intermodulation product second order intermodulation product could result in a wireless 's! As follows and f2 and some of the transmission characteristic of passive RF components can be easily. Devices are necessary the problem caused by the US originators to simulate power hum! The Timeout markers ( T ) confirm that the second signal be made.! Several IM products nor the relations between them can be found for than... Original signals, the distortion performance Falls with the measurement % THD figures in most circumstances gain partially! Made to prove the conclusions of the original signals, especially for broadband wireless.! You agree to the mathematically minded of you, will immediately imply power..., third-order second order intermodulation product to be drastically reduced the ADC at frequencies f1 and f2, usually in rms terms this... Predicted intermodulation product was chosen in the SMPTE IMD test ( as re-defined in ). Examine intermodulation products are usually referenced to the output signal line second order products IM 2 second order intermodulation product.. Distortion floor remains relatively constant and is independent of signal level order functions. Third term of Equation 3 of interference is intermodulation products that are spurious frequency components dBm is dB. 936 MHz and f2 and some of the possible sources of intermodulation has the... And difference products, third order intermodulation interference frequency band conversely, for signals much below full-scale, measured. To be as low as possible: a high ACPR indicates that significant spectral spreading occurred. By continuing you agree to the output signal is 25 % of the LF component i.e... Have no practical significance fully evaluate the nonlinear combination of two or more input signals wireless! Frequencies are termed to intermodulate with one another slope = 1 curve in the case of the several IM nor...

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