intermodulationsforvrængning

Intermodulation, or intermodulation distortion (IMD), is the creation of new frequency components when multiple signals pass through a nonlinear system. If two input tones occupy frequencies f1 and f2, the system can generate components at frequencies that are integer linear combinations of f1 and f2, expressed as |m f1 ± n f2|, where m and n are integers. In RF practice, a two-tone test is commonly used to characterize IMD. The most troublesome products are typically the third-order components at approximately 2f1 − f2 and 2f2 − f1, because they lie close to the original tones and can interfere with adjacent channels. Second-order products at f1 ± f2 can also appear when even-order nonlinearities are present, along with harmonics such as 2f1 or 2f2.

Causes of intermodulation include nonlinear behavior in active devices such as transistors and diodes, as well as mixers and other nonlinear circuit elements. Poor impedance matching, bandwidth limitations, saturation, temperature changes, and aging can increase IMD by pushing components further into nonlinear operation.

Effects of intermodulation depend on the application. In communications systems, IMD degrades dynamic range, causes adjacent-channel interference, and can raise error rates. In audio and other signal chains, IMD can introduce distortion when multiple signals share a nonlinear stage or when levels are high.

Mitigation strategies focus on improving linearity and reducing nonlinear sources. Methods include operating components within their linear region, using predistortion or feedback linearization, employing high-linearity amplifiers, and applying filtering and proper isolation to suppress intermodulation products. Rigorous testing and adherence to design standards help ensure IMD remains within acceptable limits.