Distortion intermodulation

Many parameters are important in audio devices and merit attention in the measurement process. Some common audio measurements are frequency response, gain or loss, harmonic distortion, intermodulation distortion, noise level, phase response, and transient response. 

Non-linearity in amplifiers or other parts of the system gives rise to intermodulation distortion [Sinclair, 1989],... 

Non resonant techniques are only of limited use to determine microwave losses with high precision, in particular when the losses are very small. Flowever, for the investigation of nonlinear absorption phenomena (i.e. rf power dependent on surface impedance or loss tangent) by intermodulation distortion measurements broad-band test devices are more common. Typically, a planar transmission line with an impedance of 50 Ohms can be employed for intermodulation... 

Tables in the present chapter contain in their upper part data on the spin-rotation interaction constants e q (q = Inertial axes a, b, c) and In their lower part data on the rotational constants A, B, and C. Methods of measurement, references, and remarks are the same for either constant. The quartic (A, 8 and A, 5) and sextic (O, (p) centrifugal distortion constants listed In the first table (for the electronic ground state of PHg) are defined by the A-reduced form (asymmetric reduction) of the respective Hamiltonian for spin-rotation Interaction and rotation [1 to 3]. Abbreviations used in the tables are MW for microwave absorption, EL AB for electronic absorption, LMR for laser magnetic resonance, FIR for far IR, IMF for Intermodulated fluorescence.

A class A ampMer is used in applications requiring low harmonic distortion output power. A class A ampMer can be operated with low intermodulation distortion in linear RF amplifier service. Typical plate efficiency for a class A ampMer is about 30%. Power gain is high because of the low drive power... 

A class AB power amplifier is capable of generating more power—using the same tube than the class A amplifier, but more intermodulation distortion will also be generated. A class B RF linear ampMer will generate still more intermodulation distortion, but is acceptable in certain applications. The plate efficiency is typically 66%, and stage gain is about 20-25 dB. 

FIGURE 7.45 For intermodulation distortion analysis, the amplifier undertest maybe thought of as an ideal amplifier shunted by a mixer that creates the intermodulation product components. Multiple frequency signal components make up the inputs to the mixer. 

FIGURE 7.46 Example output spectral components are shown for a teal linear amplifier with odd order intermodulation distortion. A two-frequency (two-tone) input signal is shown amplified at the output along with odd order difference frequencies generated within the amplifier. 

TABLE 7.1 Some Odd Order Intermodulation Distortion Components to the Ninth Order... 

Odd order intermodulation distortion and 1-dBm gain compression go a long way to characterize the linearity of a hnear amplifier, but they are by no means the only ones. Other distortion types tend to be apphcation specific relating to their importance. For video signals other distortion type include the following ... 

Third-order intermodulation performance for Class AB or B is generally worse than Class A, and harmonic distortion is better in the sense that even harmonics are canceled to a large degree in the primary of the output transformer. These currents flow in opposite directions at the same time and net to zero, whereas odd order harmonic currents do not. An amplifier model for a Class AB or B amphfier is shown in Fig. 7.54. Its topology is the same as that for the Class A in Fig. 7.51 except that listandardLoad(sL) inside the amplifier is replaced by liintemai or Ri t- For a maximum power efficiency, //niax = 78.5%,... 

Intermodulation distortion The result of two or more time-domain signals being multiplied together when they were intended to be only added together. Undesirable multiplication takes place in every amplifier amplifying multiple signals yielding sum and difference frequency components that are not present at the input to the amplifier. 

In an intensity modulated link the amplitude of the intermodulation terms depend primarily on the linearity of the modulation device, in this case the diode laser. The IM-free DR is defined as the maximum difference between the noise floor and the fundamental output, which produces distortion terms of equal amplitude to the noise floor. The noise floor in turn depends on the link bandwidth (BW), which varies by application. Consequently to make the IM-free DR measurements have general applicabihty, the results are often given in terms of a 1-Hz bandwidth. To use such results in a specific apphcation simply requires scaling the 1 -Hz data to the application bandwidth. The bandwidth scaling exponent depends on the order of the dominant distortion for second-order distortion, the IM-free DR scales as (BW) or the square root of bandwidth, for third-order distortion, the IM-free DR scales as (BW). ... 

Distortion is a measure of signal impurity. It is usually expressed as a percentage or decibel ratio of the undesired components to the desired components of a signal. There are several methods of measuring distortion, the most common being harmonic distortion and several types of intermodulation distortion. 

SMPTEIM A method of measuring intermodulation distortion in an audio system standardized by the Society of Motion Picture and Television Engineers. 

Intermodulation distortion The distortion that results when two or more signals interact, usually because of nonHnearities in the equipment, to produce new signals. 

Intermodulation distortion (IMD) The distortion that results from the mixing of two input signals in a nonlinear system. The resulting output contains new frequencies that represent the sum and difference of the input signals and the sums and differences of their harmonics. IMD is also called... 

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

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