Have you ever thought that the integrated digital signal processor (DSP) in an audio amplifier is only used for digital filters, equalization, or audio mixing? The reality is that the integrated DSP in modern audio amplifiers can bring more benefits, including improving the efficiency of the amplifier and audio system. Battery-powered speakers are still one of the most convenient ways to play audio, suitable for indoor, outdoor or any other occasions where music is played. In this article, I will discuss how audio amplifiers with integrated DSP can improve the efficiency of speakers and extend their run time. “How long can the battery last?” Obviously, consumers want portable speakers to

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

Battery-powered speakers are still one of the most convenient ways to play audio, suitable for indoor, outdoor or any other occasions where music is played. In this article, I will discuss how audio amplifiers with integrated DSP can improve the efficiency of speakers and extend their run time.

“How long can the battery last?”

Obviously, consumers want portable speakers to be able to play their favorite playlists or podcasts longer, and require shorter charging time. Speaker production companies have noticed this, and sometimes even list the speaker’s playing time on the retail packaging.

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

In the case that the battery capacity cannot be increased flexibly, the question faced by designers becomes “How to achieve longer playback time with a battery of the same capacity?” The answer is to improve efficiency. For audio applications, the more efficient amplifiers with medium and high power (assuming greater than 10W) ​​are still Class D amplifiers, 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 measurements in the laboratory. In fact, for a typical audio clip or song, the measured amplifier efficiency will vary continuously based on the output power provided. This is because at lower output power, the rate of power loss due to heat in the amplifier MOSFET increases. 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 this, because reducing the power supply voltage may reduce the system’s ability to provide higher output power, especially the ability to provide peak power in a higher dynamic range.

Battery life solutions for medium and high power speakers

In order to improve efficiency without affecting the output power, TI introduced the TAS5825P Class D audio amplifier using the Hybrid-Pro algorithm in the DSP. The amplifier continuously analyzes the input audio signal and provides the pulse width to the external DC/DC converter. Modulation feedback can improve system efficiency and reduce unnecessary losses. Using feedback, the DC/DC converter can increase the supply voltage when audio peaks are needed, and reduce the supply voltage when higher output power is not needed. This feature can reduce power consumption and improve efficiency when playing audio at low volume without limiting the amplifier’s ability to provide maximum output power. Figure 1 shows the block diagram of the TAS5825P.

How to improve the efficiency of audio amplifier by integrated audio amplifier DSP

Figure 1: Block diagram of TAS5825P

The Hybrid-Pro concept is very simple. It is the same as the way we try to save energy at home or at work. For example, when the light in the room is not in use, you will turn it off to reduce electricity bills. However, for audio amplifiers, you don’t want to just turn off the music! For a more precise comparison, please consider Hybrid-Pro as an automatic dimmer. The light sensor does not turn off the light (audio amplifier), but automatically dims the light so that it just reaches the brightness required at the time (the power supply voltage of the amplifier). Figure 2 illustrates this concept, where the amplifier’s power supply voltage (PVDD) increases as the required output voltage increases.

How to improve the efficiency of audio amplifier by integrated audio amplifier DSP

Figure 2: TAS5825P Hybrid-Pro envelope tracking

Enabling Hybrid-Pro running test can make battery-powered speakers achieve longer running time. Compared with a typical amplifier with a fixed voltage rail, the TAS5825P configured in Hybrid-Pro mode can extend 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 amplifiers are unprecedented. TI’s class-D audio amplifier product line with integrated DSP continues to push the limits and achieve higher system-level efficiency. Learn more about using DSP to process voice commands.

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