Crossover distortion

A reasonable assumption is that there is negligible distortion for low-level signals, ie x[n = s[n, for s[n 0 so that k0 = 1. (Note that this assumption would not be valid for crossover distortion). This model will be referred to in general as the Autoregressive-Memoryless Non-linearity (AR-MNL) model and as the AR(P)-MNL(Q) to denote a AR model of order P and a memoryless non-linearity of order... 

In Fig. 7.52 the loacUine passes through the zero collector current point of each transistor where one device is turning off and the other is turning on. At this precise point both amplifier devices could be ojf or on. To avoid this glitch or discontinuity, strict Class B is never really used, but instead, each transistor is biased on to a small value of current to avoid this crossover distortion. The choice of bias current has an affect on 1M3 so that it maybe adjusted for best IM performance under a multitone test condition. The quiescent bias current is usually set for about 1-10% of the highest DC collector current under drive. Biased under this condition, the active devices are not operating in strict Class B, but rather, in a direction toward Class A, and is usually referred to as Class AB. 

Crossover distortion A distortion that results in an amplifier when an irregularity is introduced into the signal as it crosses through a zero reference point. If an amplifier is properly designed and biased, the upper half cycle and lower half cycle of the signal coincide at the zero crossover reference. Crossover frequency The frequency at which output signals pass from one channel to the other in a crossover network. At the crossover frequency itself, the outputs to each side are equal. 

It should be noted that there is an appreciable forward voltage drop, about 0.6 volts when the current is around 1 ma. This is typical for silicon PN diodes, but diodes made from the element germanium can be made with "forward voltages" of about 0.3 volts. Completely different kinds of diode, not involving PN junctions can be made, such as Schottky diodes, and some have even lower forward voltages. (The nonlinearity at very low current is "crossover distortion.")... 

High skew rate Intermodulation distortion Harmonic distortion Phase distortion Crossover distortion... 

The Fe(III) complexes of R-substituted salicylaldehyde thiosemicarbazone (R-thsa2- Fig. 6) are among the most studied spin crossover materials of this family. The crystal structures of several of them have been determined at various temperatures. The iron-donor atom distances are compiled in Table 2. The Fe(III) ion is in a distorted FeS2N202 octahedron formed by two thiosemicarbazone ligands, which are geometrically arranged in such a way that the S and O atoms are located in cis positions, whereas the N atoms occupy trans positions, i.e. each tridentate molecule coordinates in an equatorial plane [101]. 

The comparison of Fe(III) spin transition systems with those of other metal ions reveals the greater variety of chromophores for which spin crossover is observed in iron(III). This is reflected in a generally more diverse coordination environment as well as a far broader range of donor atom sets. For six-coordinate systems the spin crossover generally involves an S=l/2<->S=5/2 change, whereas for five-coordinate materials an intermediate (quartet) spin state is involved in S=l/2<->S=3/2 transitions. There is just one report of such a transition in a six-coordinate system and that is considerably distorted [126]. 

Such doubly logarithmic plots are a common tool in visualizing crossover functions. They however give a strongly distorted picture of the physical behavior. Consider for instance the crossover from the dilute to the semidilute excluded volume behavior, which for our example takes place in the range 10-4 < s < 0.1, Figure 14.1b shows this crossover in a direct plot. Clearly... 

Spin-crossover phase transition of a manganese(IU) complex [Mn(taa)] was studied by variable-temperature laser Raman spectroscopy and it was found that the vibrational contribution in the transition entropy is not dominant in contrast to the cases of ordinary iron spin-crossover systems. The discovery of a dynamic disorder in the HS phase by means of dielectric measurements provided an alternative entropy source to explain the thermally induced spin-crossover transition. This dynamic disorder was attributed to the reorienting distortion dipoles accompanying the E e Jahn-Teller effect in HS manganese(III) ions. 

Many ferroelectric materials were found in the past. However, there is a limited number of structures that are adopted by the majority of the commercially important ferroelectric materials. In each of these structures, the ferroelectricity is tied to distortion of the coordination polyhedra of one or more of the cations in the structure. One example is the perovskite structure. Cations that seem to be especially susceptible to forming such distorted polyhedra include Ti, Zr, Nb, Ta, and Hf. All of these ions lie near crossover points between the stability of different electronic orbitals, and so may be likely to form distorted coordination polyhedra [5], Polarizable cations such as Pb and Bi are also common to many ferroelectric materials. In this case, it has been suggested that the lone pair electrons may play an important role in stabilizing ferroelectric structures. Thus the ferroelectric transition temperature and spontaneous distortion of PbTiC>3 is much larger than that of BaTiC>3. 

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