Nonlinear distortion

Nonlinear distortion is a term used (in fields such as electronics, audio and telecommunications) to describe the phenomenon of a non-linear relationship between the 'input' and 'output' signals of - for example - an electronic device. Nonlinear distortion is a term used (in fields such as electronics, audio and telecommunications) to describe the phenomenon of a non-linear relationship between the 'input' and 'output' signals of - for example - an electronic device. For many devices, a linear model is accurate only for small signal levels. For example, at 2 volts input, a typical audio amplifier might put out 20 V, meaning the linear gain is 10 V/V. For 3 V input, it might then output 30 V. However, the model implies that at 50 V input it would produce 500 V, which is not possible with most amplifiers. Mathematically, the input-output relationship of many devices should be described by a polynomial or Taylor series, as shown below. v = ∑ k = 1 ∞ a k u k {displaystyle v=sum _{k=1}^{infty }a_{k}u^{k}} For larger values of u, the higher order coefficients such as a 2 {displaystyle a_{2}} and a 3 {displaystyle a_{3}} come into play. Nonlinearity can have several effects, which are unwanted in typical situations. The a 3 {displaystyle a_{3}} term for example would, when the input is a sine wave with frequency ω {displaystyle omega } , result in an extra sine wave at 3 ω {displaystyle 3omega } , as shown below. v = ( a 1 + 3 4 a 3 ) s i n ( ω t ) − 1 4 a 3 s i n ( 3 ω t ) {displaystyle v=(a_{1}+{frac {3}{4}}a_{3})sin(omega t)-{frac {1}{4}}a_{3}sin(3omega t)} In certain situations, this spurious signal can be filtered away because the 'harmonic' 3 ω {displaystyle 3omega } lies far outside the frequency range used, but in cable television, for example, third order distortion could cause a 200 MHz signal to interfere with the regular channel at 600 MHz. Nonlinear distortion applied to a superposition of two signals at different frequencies causes the circuit to act as a frequency mixer, creating intermodulation distortion.