Intermodulation Distortion in Amplifiers
Abstract:
Two components of the distortion produced in a wideband amplifier, such as a receiver multicoupler, are considered for the case when the input contains signals at two or more frequencies. These components of distortion are combination frequencies and cross modulation. The combination-frequency also known as sum-and-difference-frequency signals appear at frequencies which are the sum and difference of the input frequencies and their multiples. It is shown that the amplitude of these signals is related to the amplitude of the harmonic distortion produced in a nonlinear amplifier. With two input signals of approximately equal amplitude, the combination-frequency signals will be several times greater than the corresponding harmonics. Cross modulation or crosstalk is a result of the dependence of the amplification of one signal upon the amplitude of another signal in a nonlinear circuit, and causes modulation from one carrier to appear on another carrier. This effect is approximately proportional to the third-harmonic distortion produced by the interfering signal and is practically independent of the amplitude of the signal being interfered with. KAR P. 4