> 4.6 | Decoupling the Speaker Signal

> The speaker signal is balanced. Due to ground bouncing between module and other GND this signal cannot be simply used as unbalanced signal (see also Section 4.9.1). Therefore it is recommended to apply an opamp which transforms the GND reference point. Because of the low gain C3 and C4 are needed for compensation.
> Figure 18: Circuit for transforming balanced into unbalanced – sample 1
> R5 in this picture protects the opamp against RF coming from other circuits.
> Often a simpler circuit for transforming balanced into unbalanced signals is sufficient. The circuit according to Figure 19 is suitable e.g. for connecting the balanced outputs to an audio codec, like AC97, if no digital audio interface can be used.
> Figure 19: Circuit for transforming balanced into unbalanced – sample 2
> Figure 20 shows a sample circuit of headsets connected to the GSM module. C10, R1, R2 avoid RF-demodulation at the output of U1 (see also Section 4.9.2).
> Figure 20: Circuit for connecting a headset