> 4.9.2 | RF Related Audio Problems

> Figure 26: TDD noise/humming in the output spectrum
> The microphone should be equipped with two internal EMI capacitors for GSM 900/1800 MHz bands (12…18pF + 33pF).
> Semiconductors are always a source of RF demodulation. This behavior can only be cancelled by hardware and layout changes!

> • | Each semiconductor (e.g. ESD diodes etc.) needs to be RF-decoupled using a capacitor from 10 to 33pF.

> • | Serial resistors >50Ohms including the internal capacitance of the semiconductor (e.g. opamp or analog switches etc.) act as low pass for GSM frequencies (see Figure 27).

> • | On the PCB, these capacitors and resistors shall be placed close to the semiconductor and/or input pins.

> Figure 27: Recommended serial resistors for semiconductor inputs