Have you ever thought that the integrated digital signal processor (DSP) in the audio amplifier is only used for digital filter, equalization or audio mixing? The reality is that the DSP integrated in modern audio amplifiers can bring more benefits, including improving the efficiency of amplifiers and audio systems.

    Battery powered speakers are still one of the super convenient audio playback methods, which are suitable for indoor, outdoor or any other occasions to play music. In this article, I will discuss how an audio amplifier with integrated DSP can improve the efficiency of speakers and prolong their running time.

    Obviously, consumers want portable speakers to play their favorite playlists or podcasts more permanently, and the charging time is shorter. Speaker manufacturing companies have noticed this and sometimes even listed the playback time of speakers on the retail package.

    If battery life is so important for portable speakers, you should choose a larger battery, right? This is true for some designs, but there is not enough space for compact speakers at all. Alternatively, additional battery capacity may significantly increase the system cost.

    When the battery capacity cannot be flexibly increased, the problem faced by designers becomes "how to use the battery with the same capacity to achieve longer playback time?" The answer is to improve efficiency. For audio applications, the more efficient amplifier of medium and high power (assuming greater than 10W) is still class D amplifier, with a theoretical efficiency of 100% (actually greater than 90%).

Although efficiency greater than 90% is the benchmark, this is usually the result of constant input signal and output power measurement in the laboratory. In fact, for a typical audio clip or song, the measured amplifier efficiency varies according to the output power provided. This is because at lower output power, the ratio of power loss due to heat in the amplifier metal oxide semiconductor field effect transistor will increase. In order to reduce these unnecessary losses, the simplest solution is to reduce the voltage of the power supply. For audio, designers may be reluctant to do so, because reducing the power supply voltage may reduce the ability of the system to provide higher output power, especially the ability to provide peak power in higher dynamic range.

    In order to improve the efficiency without affecting the output power, Ti has introduced tas5825p class D audio amplifier using hybrid Pro algorithm in DSP. The amplifier can improve the system efficiency and reduce unnecessary loss by continuously analyzing the input audio signal and providing pulse width modulation feedback to the external DC / DC converter. Using feedback, the DC / DC converter can increase the power supply voltage when the audio peak is required and reduce the power supply voltage when higher output power is not required. This function can reduce power consumption and improve efficiency when playing audio at low volume without limiting the ability of the amplifier to provide maximum output power. Figure 1 shows a block diagram of tas5825p.

 
   The concept of hybrid Pro is very simple. It is the same as the way we try to save energy at home or at work. For example, when you do not use a light in a room, you turn it off to reduce your electricity bill. However, for the audio amplifier, you don‘t want to just turn off the music! For a more accurate comparison, think of hybrid Pro as an automatic dimmer. The light sensor does not turn off the light (audio amplifier), but automatically dims the light to just reach the brightness required at that time (power supply voltage of the amplifier). Figure 2 illustrates this concept, in which the power supply voltage (PvdD) of the amplifier increases as the required output voltage increases.

    Enabling hybrid pro to run tests allows battery powered speakers to run longer. Compared with a typical amplifier with a fixed voltage rail, the tas5825p configured in hybrid Pro mode can prolong the battery life by more than 20%. In addition, the adjustable audio look ahead buffer in the tas5825p provides advanced voltage rail control without the risk of audio clipping.

    Although DSP was only used for equalization and audio filtering in the past, the benefits of integrating DSP in audio amplifier are unprecedented. Ti has class D audio amplifier product series with integrated DSP, constantly breaking through the limit and realizing higher system level efficiency.