QUESTION

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My LTE CatM1 board has passed TRP/TIS but failed RSE. Harmonic in Band12. How do I determine what is the root cause?

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Hi Roberto D,

When determining the root cause of Radiated Spurious Emission issues, it’s important to figure out whether the problem is derived from an intentional radiator or an unintentional radiator.

An intentional radiator RSE is commonly due to harmonics of the transmitted signal and thus are rooted in the transmitter of the wireless device.

               Typical causes:

                              Local Oscillator Leakage

                              Signal Chain Non-Linearity

                              Amplifier Non-Linearity

                              No Filtering in Signal Chain

                              Mixing Products

An unintentional radiator RSE comes from non-transmitter sources and can be classified as everything else on the device.

               Typical causes:

                              Oscillators (Clocks)

                              Memory Interfaces (DDR)

                              Microcontrollers

                              Display interfaces

                              Switching power supplies

A spectrum analyzer, shielded enclosure, low noise amplifier, and EMC probes can be used to determine the source of the radiator by probing different areas of the device within the isolated environment of the shielded enclosure. You can start with the transmitter off first to help narrow down whether the RSE is transmitter related; then with it on (and potentially pushing traffic) while you probe the device to locate the source. Once the source of the RSE is located, mitigation methods would involve PCB layout techniques, shielding, signal filtering, or some combination of thereof.

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edited ago by
A harmonic can have many reasons. If the matching is not perfect it can lead to harmonics. If too few vias have been used then for that often harmonics as well. If you like, we can check your PCB layout for you at a reasonable price.

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