Silicon Substrate Surface Conduction and Dielectric Passivation Fundamentals
Trap-rich polysilicon passivation pins interface charges on high-resistivity silicon, suppressing surface conduction and harmonic spur spikes across RF switches.
Second Harmonic Spur
Meaning
An unwanted signal generated at exactly twice the frequency of the intended transmission represents a major source of electromagnetic interference. Radio designers must suppress the second harmonic spur to meet the strict emission limits set by telecommunications regulatory authorities. This suppression prevents the transmitter from disrupting other wireless services operating at higher frequencies.
Generation Cause
Asymmetrical distortion in the power amplifier or the switching circuits represents the primary source of even-order harmonic energy. When the transistor operates close to saturation, the output waveform becomes clipped, generating these unwanted frequencies. Measuring the second harmonic spur allows engineers to evaluate the linearity of the transmitter chain.
Filter Solution
Lowpass or bandpass filters placed between the power amplifier and the antenna are designed to attenuate these high-frequency spurious emissions. These passive filters must offer high out-of-band rejection while maintaining low insertion loss at the fundamental frequency to avoid wasting transmitter power. Proper shield placing on the circuit board prevents the spur from bypassing the filter through radiative coupling.
Compliance Testing
During the certification process, the device is placed in an anechoic chamber and tested for radiated spurious emissions. Special receiver sweeps are performed to check for any signal peaks at double the carrier frequency of the active transmitter. Developers must ensure that the second harmonic spur remains below the maximum allowed decibel level to pass the regulatory audit.
Passing this test is a mandatory requirement before the product can be legally sold in commercial markets and deployed in public communication networks.