What is AM Distortion?
AM distortion (Amplitude Modulation distortion) is an undesirable form of signal degradation caused by amplitude variations in a communications system. It occurs when non-linear components — particularly power amplifiers — alter the amplitude relationship between input and output signals, introducing harmonics and intermodulation products that corrupt the transmitted waveform. AM distortion is especially problematic in OFDM-based systems like 5G NR, where high peak-to-average power ratios make signals particularly susceptible to amplitude non-linearity.
How Does AM Distortion Work?
AM distortion arises when a power amplifier operates near its saturation point. The transfer function between input and output power becomes non-linear, causing gain compression — where increases in input power produce progressively smaller increases in output power. This non-linearity generates spectral regrowth (energy spreading into adjacent channels) and in-band distortion (constellation point displacement). It is characterised by AM/AM conversion curves and managed through techniques such as output power back-off and digital pre-distortion (DPD).
Use Cases
Power amplifier linearization and DPD design, transmitter signal quality testing, EVM root-cause analysis, 5G NR base station and UE RF performance optimization, and wideband signal integrity assessment for carrier aggregation scenarios.
3GPP / Standards Reference
3GPP TS 38.104 (NR BS radio transmission), ITU-R SM.1541 (Unwanted emissions in the out-of-band domain)
Related Terms
AM distortion | EVM | PAPR | ACPR | Beamforming
Learn More
This glossary entry is part of the 5GWorldPro Complete 5G Glossary. To go deeper into 5G architecture and technology, explore our 5G Training courses.
