Meaning
Generation of an unwanted signal at three times the fundamental frequency of the input signal occurs due to odd-order non-linearities in electronic components or substrates. The level of third harmonic distortion is a critical measure of the symmetric non-linearity in radio-frequency front-end modules. This parameter is bounded by the saturation power of the active transistors and the intrinsic linearity of the passive structures, which limits the maximum error-free power that can be transmitted.
Spectral Impact
Odd-order harmonics are particularly problematic because they can generate intermodulation products that fall directly within the band of the receiver. This can desensitize the receiver and degrade the signal-to-noise ratio. Minimizing these signals is essential for maintaining clear voice and data transmission.
Substrate Engineering
Symmetric non-linear capacitance at the buried oxide interface of silicon-on-insulator wafers is a primary cause of this distortion. Implementing a trap-rich layer captures the mobile carriers and prevents the non-linear modulation of the interface. This maintains the substrate linearity even under high-power conditions.
System Testing
High-power transceivers require rigorous verification of these emission levels using multi-tone test setups. Automated test benches measure the output spectrum under maximum input power to ensure compliance with wireless standards. This ensures the device operates reliably without interfering with adjacent communication channels.
