The third order intercept point relates nonlinear products. There are two key measurements in determining power amplifier quality, efficiency, and linearity. Since the noise of the adc isto firstorder approxima tionindependent of signal level, the higher the input level the better the snr, up to a point. The second and thirdorder intercept points ip2 and ip3 are figures of merit for these specifications and allow distortion products to be computed for various. This response can be written to the third order nonlinearity as. The third order law says that the intermodulation product grows with the input amplitude raised to a power of three. The intercept point can be determined by measuring and plotting both the fundamental signal and an. P1db vs toi1db compression point,third order intercept point. In reality, the intercept power is 10 to 15 dbm higher than the p1db gain compression power, so the circuit does not amplify or operate correctly at the iip3 level. In telecommunications, a third order intercept point ip 3 or toi is a measure for weakly nonlinear systems and devices, for example receivers, linear amplifiers and mixers. It is an interpolated point where the fundamental component power curve meets the second order intermodimd2 component power curve consider a nonlinear amplifier whose inputoutput characteristic is represented by a 3 rd order polynomial given by 1. Third order intercept point is just one of several specifications that can be. It is a theoretical point, where the intermodulation products at the duts output grow as large as the original tones at the dut output side.
Since the power slope is known for both the fundamental signal slope. Calculate the intermodulation distortion products imd3 arising from third order nonlinearities third order intercept point, ip3 in rf receivers under twotone input. Ip2 vs ip3 difference between second order intercept. Whats the difference between the thirdorder intercept. Third order distortion causes multiple unwanted products. Pdf on upper bound for the third order intercept point. Ip3 may be given as the input level or as the output level for that point and which one has to be specified. One uses the terms input intercept point iip3 and output intercept point oip3. The input power level is known as iip3, and the output power when this occurs is the oip3 point. At high bias voltage, the thirdorder intercept point ip3 of the waveguide photodiode is constant at low frequency and. Behaviors of the third order intercept point for pin waveguide photodiodes article pdf available in optics express 1716. Additionally, the socalled third order intercept point ip3 can be calculated. Intercept point, gain compression and blocking university of.
Reviewing the basics of intermodulation distortion. In telecommunications, a third order intercept point ip 3 is a specific figure of merit associated with the more general third order intermodulation toi distortion, which is a measure for weakly nonlinear systems and devices, for example receivers, linear amplifiers and mixers. However, it is useful in determining the linearity condition of an amplifier. Block 1 has a gain, g1, at rf and an equivalent third order input intercept point iip31. Note that for a 10db backoff from theip3 point, the im3 improves 20db. Pin, pout, iip3 and oip3 are the input and output power and third order intercept point, respectively. The output intercept point equals the input intercept point plus the device gain.
Device a has a thicker absorber and shorter length, resulting in a bandwidth of 20 ghz while device b reduces the absorber by half while maintaining. In practice, we usually refer all quantities to the input. Ip3 3rd order intercept point is a theoretical figure of merit describing the 3rd order distortion performance of a circuit. It is based on the idea that the device nonlinearity can be modeled using a low order polynomial, derived by means of taylor series expansion. Imd measurement with e5072a ena series network analyzer. The lt5575 also has high 3rd order linearity and a low noise figure of 12. Once the ip3 point is known, the im3 at any other power level can be calculated. The nth order intercept point ipn is where the asymptotes for the nth order intermodulation product and the fundamental cross. Well, ip3 is a figure of merit for comparing amplifiers.
F2 f12f1 f2 2f2 f1 deltaf im3 relative to carrier dbc fundamental pf1 pf2 p2f1f2 frequency ip3 can be calculated by the equation using lowside im3. Simple model for fundamental a intermodulation analysis of. Cascaded budget 2tone, 3rdorder intercept point ip3 rf. Traditional definitions of the nth order intercept point. The computation is performed over a periodogram of the same length as the input using a kaiser window with. Skript zum thema mischer pdf intercept point, gain compression and. Iip3 mentioned above is the 3rd order intercept point at the input of the amplifier for oip3 output third order intercept point. Second order intercept point ip2 is a used to quantify weak nonlinearity in an amplifier or rf system. Calculating noise figure and thirdorder intercept in adcs introduction noise figure nf and the thirdorder intercept point ip 3 are used in radio receiver link budget analysis as a means to quantify the effects of device noise and nonlinearity on the sensitivity of the radio. Higher ip3 values indicate that the amplifier is more linear, and will generate fewer output tones, otherwise known as intermodulation products. The extrapolated point where the curves of the fundamental signal and third order distortion product signal meet is the intercept point ip3. These intercept points are observed in saturated amplifier gain response. When amplifier operates in non linear region or when it is over driven it generates intermodulation products of input signals fed at the input. It is based on the idea that the device nonlinearity can be modeled using a low order polynomial, derived by means.
In figure 4, the gain is normalized to unity so input ip2 output ip2 iip2 oip2. Third order intercept point versus temperature fig 12. Plot of intermodulation is assumed in the form of straight lines small signal approach, with slopes 1 and 3. Block 2 has a gain, g2, at if and an equivalent third order input intercept point iip32. Most radio physical level protocols have ip3 requirements as part of the receiver specifications. Through twotone simulation at the same quiescent bias, the simulated third order intercept point is 5. Figure 4 below shows the third order intercept value as a function of frequency for a typical wideband lowdistortion amplifier.
Third order intercept point the third order intercept point is the imaginary extrapolated point where the amplitude of a desired signal output from a device is equal to the amplitude of an unwanted output. Calculating noise figure and thirdorder intercept in adcs. The formula is useful in order to characterize linearity of a rf receiver for signals below the saturation level. In telecommunications, a thirdorder intercept point ip 3 is a specific figure of merit associated with the more general thirdorder intermodulation toi distortion, which is a measure for weakly nonlinear systems and devices, for example receivers, linear amplifiers and mixers. A power series describes all of the possible combinations of generated frequencies. This page on ip2 vs ip3 describes difference between second order intercept point ip2 and third order intercept point ip3. Ip3 is the most commonly used intercept point, but others, including ip2. Second order intercept point ip2 analogrf intgckts. The thirdorder intercept point ip3 or the thirdorder intercept toi are often used as figures of merit for imd. Ip3o output third order intercept point f 450 mhz 5. Analogtodigital converters adcs are used in radio receivers to convert the. Thrid order intercept point ip3 is a used to quantify weak nonlinearity in an amplifier or rf system. Cascaded 2tone, 3rdorder intercept point ip3 when two or more tones are present in a nonlinear device, intermodulation products are created as a result.
Input third order intercept point for crystal filters. The third order intercept point ip3 is the point at which the the extrapolated third order intermodulation level im3 is equal to the signal levels in the output of a twotone test when the extrapolation is made from a point below which the third order intermodulation follows the third order law. Order intercept point an overview sciencedirect topics. All measurements done on characterization board without matching, deembedded up to the. It is an interpolated point where the fundamental component power curve meets the third order intermodimd3 component power curve consider a nonlinear amplifier whose inputoutput characteristic is represented by a 3 rd order polynomial given by 1. Third order intercept point ip3 the third order intercept point ip3 or the third order intercept toi are often used as figures of merit for imd. 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. In this test, the difference between 1db compression point and third order intercept point is 12db. Waveguide pin photodiodes with different absorber thicknesses and lengths were fabricated and characterized for linearity. In the presence of strong signals even a few db of input attenuation is often enough to drop the ips back into the noise, while afflicting the desired signals only a. The power level of each of the two offchannel cw interferers present at the receivers input is assumed to equal pi, which is the. The second order intercept point is called ip2 and the third order intercept point is called ip3.
Pdf download nov 26, 20 there are two key measurements in determining power amplifier quality, efficiency, and linearity. The measurement of the 3rd order intercept point is illustrated in figure 2. Receiver second and third order intercept points are typically much greater than the 1db compression points, but there is no reliable method for predicting one value from the others. This is fictitious signal level at which the fundamental and third order product terms would intersect. Intermodulation distortion considerations for adcs pdf. The ip3 value must be much greater than both tone levels for the calculation to be meaningful. By convention, in any 2tone test including third order intercept point ip3 tests, the power levels plotted refer to one of the input tones and one of the output product tones.
Calculating noise figure and third order intercept in adcs introduction noise figure nf and the third order intercept point ip 3 are used in radio receiver link budget analysis as a means to quantify the effects of device noise and nonlinearity on the sensitivity of the radio. Dynamic range is a key parameter in electronic systems, but one that is often difficult to compare at the component level when trying to design a system for optimum performance. Often it is assumed that the tones are at the exact same level and the im products are identical. For example, the input ip3 is represented as iip3, whereas the output ip3 is represented as oip3. Third order intercept point third order intercept point ip3 is a term sometimes heard when amateur radio operators are discussing the qualities, or lack thereof, of a receiver. In order to prove the simple mathematical relationship, a crosscoupled differential pair was implemented as a fully. Ip3 is the point where 3rd order products would overtake fundamentals in output power. Im3 is dependent on the amplitude a of the input tones. I also feel that the example given for tones 15db below the intercept point is wrong for 3rd order products. Interestingly, one receiver feature that can help reduce ip levels is the use of a frontend attenuator or input attenuator. Analogtodigital converters adcs are used in radio receivers.
The frequency behavior of the thirdorder intercept point in a. It is a theoretical point that is never achieved in practice. This point is the third order intercept point toip. In this case, the 3rd order distortion products will be 30db down on the signal and 45db below the intercept point.
Two receivers with identical 1db compression points may have third order intercept points which differ from each other by as much as 20 db, and vice versa. According to the article, the nonlinearity is modeled using polynomial series expansion taylor series. Finding the ip3 point the third order intercept point. A simple technique for iip3 prediction from the gain. In figure 2, this is the intersection of the dotted lines. The intercept points are further defined with respect to the input amplitude or the output amplitude where the intersections occur. Pdf behaviors of the third order intercept point for pi. The most important linearity specification for direct conversion mixers is the 2nd order intercept point iip2 due to the 2nd order distortion product falling within the baseband output spectrum, and the lt5575 boasts 54. Maxim design support technical documents tutorials. Pin curves are extrapolated out, the interception point is called the 3rd order intercept point ip3.
202 1284 214 1438 991 686 222 1254 272 1367 127 212 1319 310 917 1451 863 270 1266 560 458 1149 1136 1485 143 39 537 969 778 98 233 614 936 212 1153 1464 745 1440 312 67 182 1251 1044 290 172 1195