8.4.2.4.2 Considerations for Setting the Speaker Amplifier Gain Structure

Configuration of the gain of the amplifier is important to the overall noise and output power performance of the TAS5760LD. Higher gain settings mean that more power can be driven from an amplifier before it becomes voltage limited. Moreover, when output clipping "at the rail" is desired, it becomes important that there be enough voltage gain in the signal path to drive the output signal above the PVDD level in order to "clip" the output signal at the PVDD level in the output stage. Another desirable aspect of higher gain settings is that the dynamic headroom of an amplifier is increased with higher gain settings, which increases the overall dynamic audio quality of the signal being amplified.

With these advantages in mind, it may seem that setting the gain at the highest setting available would be appropriate. However, there are some drawbacks to having a gain that is set arbitrarily high. The first drawback is that a higher gain setting results in increased amplification of any noise that is present in the signal path. If the gain is set too high, and the speaker is sensitive enough, this may result in an audible "hiss" at the speakers when no audio is playing. Another consideration is that the speakers used in the system may not be rated for operation at the power levels which would be possible for the given PVDD supply that is present in the system. For this reason it may be necessary to limit the voltage swing of the amplifier via a lower gain setting to reduce the voltage presented, and therefore the power delivered, to the speaker.