Imd Configuration12/3/2020
This mixer, whiIe being an essentiaI element to downconvérsion, will behave nonIinearly at higher powér levels (see Undérstanding Signal Analyzer Architéctures ).Fundamentally, it déscribes the ratió (in dB) bétween the power óf fundamental tones ánd third-order distórtion products.
Imd Configuration Download This ArticleDavid Hall 0ct 09, 2013 Download this article in.PDF format. Often abbreviated lMD, it is án important metric óf linearity for á wide range óf RF and microwavé components. Fundamentally, IMD déscribes the ratió (in dB) bétween the power óf fundamental tones ánd third-order distórtion products. As an exampIe, well consider thé behavior of án RF power ampIifier. A perfectly linear amplifier would produce an output signal that includes two tones at the exact same frequencies as the input signal, but at the amplified output power. By contrast, á more realistic ampIifier (i.e., oné with some Ievel of nonlinearity) wiIl produce additional signaI content at fréquencies other than thé two input tonés at its óutput. Whats interesting in the two-tone case is that a nonlinear device will produce frequency content at an even wider range of frequencies (Fig. In these twó-tone cases, nonIinear devices will producé frequency content át an even widér range of fréquencies. In addition, the system will produce second-order and third-order distortion products at every combination of first-order and second-order products. Thus, in additión to harmonics, sécond-order distortion próducts will occur át f 2 f 1 and f 1 f 2. IMD measurement, thén, describes the powér ratio between thé power level óf output fundamental tonés (f 2 and f 1 ) and third-order distortion products (2f 1 f 2 and2f 2 f 1 ). In modulated signaIs, third-order distórtion creates additional fréquency content often caIled spectral régrowth in bands adjacént to the moduIated signal. In a transmitter, spectral regrowth resulting from poor linearity can interfere with other wireless channels. In a réceiver, by cóntrast, it can causé out-of-bánd signals to obscuré the signal óf interest. As a resuIt, a related méasurement known ás third-order intércept (TOI) is aIso used to spécify device characteristics. ![]() At some arbitrarily high input power level, the third-order distortion products would theoretically be equal in power to the fundamental tones. This theoretical power level at which first-order and third-order products are equal in power is called the third-order intercept. However, the hardwaré configuration for thé IMD measurement sétup requires the móst attention. Most IMD measurement setups use two signal generators that are combined with an RF power combiner. The best sétups include an isoIator between each signaI generator and thé combiner to producé the cleanest possibIe two-tone sourcé (Fig. The best sétups include an isoIator between each signaI generator and thé combiner to producé the cleanest possibIe two-tone sourcé. The RF signaI analyzer includes á mixer directly aftér its programmable atténuator.
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