Increasing importance of boost audio amplifier
However, the broad trend to include stereo in smartphones does not necessarily ensure a high-quality audio experience. For this purpose, the micro horn shall also be equipped with an intelligent boost audio amplifier to maximize the loudness of the horn while protecting the horn from damage. Smart phone audio designers should use high-voltage audio amplifier, horn monitoring analog-to-digital converter (ADC) and advanced algorithm to keep micro horn in safe operation state to ensure better, louder and clearer audio sound. In addition, two horns usually mean two amplifiers. Therefore, size, efficiency, battery current management, and audio performance are all twice as important. Therefore, as smart phones move towards stereo, the audio amplifier that did not appear before plays a more important role.
The following is a design list to ensure that the smart boost audio amplifier can play its maximum role.
Size - board space is always a consideration when integrating various functions into portable devices. One option is to place two miniature speakers on the top and bottom of the phone. The audio amplifier must be smaller and more integrated, especially when there are now two. In order to solve the size problem, cirrus logic uses 55nm technology to design its latest cs35l41 intelligent boost amplifier with DSP, making it easier for OEMs to adopt the dual horn design without sacrificing the space required for other new functions.
Efficacy - SAR insight research also confirmed that class D audio amplifiers have almost replaced class AB amplifiers in many markets due to the improved efficiency of class D audio amplifiers. Higher efficiency can also be achieved in the design. For example, cirrus logic‘s 11 volt boost class D amplifier also uses a class H DC-DC converter to enhance supply more efficiently than Class G, while additional battery management systems predictably adapt to changing audio, speaker, and battery conditions to regulate battery current and save power. This emphasizes the evolving technology and "enhancement" role of the boost audio amplifier, as shown in Figure 2.
Figure 2: Class G and class H supply rail voltage vs time
Horn protection - according to SAR insight & consulting, in many applications using small horns, such as smart phones, it has become more and more common for embedded DSPs in amplifiers to use horn protection algorithms. These algorithms can achieve higher output without damaging the horn. For example, the cirrus logic audio amplifier achieves more than 5 watts in a 1-Watt horn. This new boost audio amplifier can provide the power required for higher offset to generate louder and clearer audio, especially on hands-free phones, without damaging the subminiature speakers. The SAR insight report further pointed out that "since 2013, the use of horn protection in mid-range smartphones has grown rapidly, because OEMs want to maximize horn performance and combine it with other enhancements (such as high-end codecs) to achieve differentiated design."
Audio enhancements - even with all these features, not all audio enhancements are the same. In order to produce better definition and enhanced stereo audio to match those vivid, larger screens and visual content, advanced algorithms in integrated DSP should also solve audio design problems, such as equalization, compression and psychoacoustic enhancement, to fine tune audio playback.
As users abandon traditional cable or satellite TV and want to see more unrestricted content, smartphones and other mobile devices are rapidly becoming the main platforms for streaming media and content appreciation. In order to match the clearer and brighter visual experience, more and more mobile phones are shifting from mono or mono audio design to dual channel stereo to provide a better listening experience. With the continuation of this trend, the demand for intelligent power amplifier becomes more and more important. This means that smart phone OEMs will not only seek to save space in the headset and hands-free mode, but also seek to improve energy efficiency and audio clarity, so that their products can stand out in the market competition.
1 the data comes from the audio power amplifier report released by Peter conney, chief researcher of SAR insight & Consulting in the fourth quarter of 2017: market growth, channel number, amplifier type, input type, class and horn protection. The updated data comes from the audio signal chain IC forecast database released by SAR insight & Consulting in the first quarter of 2019.