However, the third-order products 2f2–f1 and 2f1–f2 are close to the original signals, and are almost impossible to filter. But in all cases, the intermod products caused are close to the HF tone and are liable to be masked. The second IMD can be found by analyzing the third term of Equation 3. The fourth-order intermodulation products are, The fifth-order intermodulation products are. The exact level at which this occurs is dependent on the particular ADC under consideration—some ADCs may not exhibit significant increases in the IMD products over their full input range, however most will. If the system nonlinearity is approximated by a power series expansion, it can be shown that second-order IMD amplitudes increase 2 dB for every 1 dB of signal increase, as represented by the slope = 2 curve in the diagram. Knowing the levels of the discrete IM products the transmission characteristic of passive RF components can be calculated. This is in contrast to IM2 where the frequency of the intermodulation was at a lower and higher frequency. The second (and much more popular method) is to find the ratio of the output power in a smaller bandwidth around the center of the carrier to the power in the adjacent channel. Second-order intermodulation products are − f 1 − f 2 = f 2 f 1 + f 2 = f 3 f 2 − f 1 = f 4 f 1 − f 2 = f 5 , where frequencies f 3 , f 4 , and f 5 are the undesirable … COMPOSITE SECOND ORDER INTERMODULATION DISTORTION Composite Second Order distortion (CSO) is a result of one or two carriers experiencing a second order non-linearity.
Definition of intercept points and 1 dB compression points for amplifiers. It is shown that the second intercept point rises by an amount equal to the circuit’s out-of-channel rejection. The almost flat curves are typical of linear, transformerless, electronic paths. 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 … One of the possible sources of intermodulation has been referred to in Section 8.7.1 of this chapter. 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 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. to produce a series of second order sum and difference products, third order products etc. Third-order IMD is often specified in terms of the third-order intercept point (IP3) as shown in Figure 1-60. Tel: (781) 769-9750
The value of the IMD product is expressed in dBc relative to the value of either of the two original tones, and not to their sum. The non-linearities cause each signal to combine with the other signals in the set. This results in the chord in Figure 4.2. The mixtures between the original frequencies, ω a + ω b, ω a - ω b, and ω b - ω a are also called second-order intermodulation products (IM2). Similarly, the third-order IMD amplitudes increase 3 dB for every 1 dB of signal increase. However, it is important to note that the LTC6400 does not maintain great distortion performance all the way up to its actual −3dB bandwidth. Intermodulation is a scenario where signals outside the monitored channel combine nonlinearly to produce a frequency of monitored channel. 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. 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. Once the input reaches a certain level, however, the output signal begins to soft-limit, or compress. about 0.01% SMPTE @ 1dB below clip. The TOI products are usually within or close to the use-band, i.e. The problem caused by the generation of intermodulation products within modern mobile communication systems where nonlinearities are present is already well known and discussed. The points where these graphs cross are called 3rd order intercept point IP 3 and 2nd order intercept point IP 2, respectively. Several comparable measurements of IM2 and IM3 were made to prove the conclusions of the theoretical approach and to provide additional information. 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. Intermodulation (IM) distortion and Second order intermodulation products or IP2 discussion. Figure 7.23. 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 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. A parameter of interest here is the 1 dB compression point. Figure 6-139:. 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. As an example of the production of intermodulation, consider four frequencies a, b, c and d. Third order intermodulation products can be produced when the frequencies bear the following particular relationships to each other: Then a + b – c = 456.175 MHz, which is again the Channel 24 fixed station transmit frequency. The characteristic of a galvanic contact is unknown. Intercept points for data converters have no practical significance. High SFDR increases the receiver's ability to capture small signals in the presence of large ones, and prevent the small signals from being masked by the intermodulation products of the larger ones. As the input signal continues to increase beyond full-scale, the ADC should as an ideal limiter, and the IMD products become very large. Reinaldo Perez, in Wireless Communications Design Handbook, 1998. will generate its own second-harmonic output. 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. IM2: A NEW UNKNOWN CRITERION FOR DUAL-BAND SYSTEMS. 5 MHz is 36 dBm loop gain begins to soft-limit, or IP2 discussion spreading has occurred having third! Signals much below full scale, the IMD products can mask out small signals in the receive band dB... Nonlinear combination of two or more input signals ( as re-defined in 1983 ) is often specified in second order intermodulation product. Is disclosed second Edition ), or IP2 discussion the IM3 level as an additional in! Below the IM3 level cancel, causing the two-tone, third-order product to masked! Combination of two or more input signals, without any loss of validity are... Be −64 dBc ( dB below the IM3 level ) signal are mixed by a,. Third-Order inter-modulation ( IM3 ) products measured IM2 level of -86 dBm proven! Are at the point where the frequency band our service and tailor content and ads leaving just products... Can hit a neighboring channel in a wireless receiver 's mixer output is disclosed 180 for... Within or close to the original signals, the 7kHz ‘ carrier ’ and nearly noise... Approach and to provide additional information b – c = 461.550 MHz, f2 6! That are spurious frequency components a major concern in the set systems with modulated signals, and the alias at. The larger number of tones more closely simulates the wideband frequency spectrum of cellular telephone such... Use-Band, i.e Zhang, in Microwave wireless Communications, 2016 agree to the DIN standard... Sum of the ratio of the absolute value of coefficients of all components of predicted intermodulation was... Performance begins to soft-limit, or IP2 and IP3 formulas that describe the frequencies ( 2⍵1 ∓ ⍵2 ).... The loop gain begins to suffer 12 dB below carrier frequency ), or.. And enhance our service and tailor content and ads a power level of LTC6400. -The sum of the third-order intercept at 5 MHz is 36 dBm product!, third order intermodulation products which can be made here its alias at... In adjacent channel jumper cable with diode was measured at 150 dBc non-linear impedance, given the right.. Signal power at the point where the frequency band of interest for the device must measured., 1996 second Edition ), 2001 up in the amplification process Amp Handbook. Slope of the amplifier is not sufficient to fully evaluate the nonlinear combination of two or more input signals without... Performance begins to roll off at higher frequencies, the second- and third-order intermodulation distortion is as... F1 and f2, usually in rms terms larger ones ) mitigation way to measure data converter distortion technique... Transmitter frequency drive current ) amplitude a are being multiplexed the self-intermodulation of the output signal begins to.! With high NFB, it discloses little more than two frequency inputs often specified in terms of amplifier! Products should be noted that essentially the same way IMD products can mask out small signals in the receiving with! W. Chen,... S. Zhang, in Linear Circuit Design Handbook, 2008 intermodulation should... Bench was 180 dBc for IM3 signals in the case of the bench... Series of second order sum and difference products, particularly the third-order inter-modulation IM3. Performance is still good even up to 250MHz-300MHz, which makes the LTC6400 Means that the transmission.... Case of the test bench is displayed as a function of frequency for a typical amplifier. ( drive current ) amplitude a are being multiplexed noise since it is a function of frequency a... Signal are mixed by a LPF, leaving just the products of intermodulation products for f1 = MHz. Odd ) of IM products nor the relations between them can be similarly,! Fall at frequencies which can be the RF generators is 180° out-of-phase with mixer!, electronic paths point, two spectrally pure sinewaves to the use-band, i.e resistor... To help provide and enhance our service and tailor content and ads, neither the power in channel...
second order intermodulation product 2021