Cirrus Logic: Why smart power audio amplifiers are increasingly important for smartphones

There seems to be no end to what people consume on smartphones, tablets or other portable devices. As smartphone screens become larger, brighter, and provide a better overall visual experience, consumers are experiencing mobile content in entirely new ways, not just through headphones. It’s common for friends to get together and turn their phones sideways to watch videos using the phone’s external speakers, sharing the experience of watching and listening. Many phones have gotten larger screen sizes over the years, but the audio experience doesn’t always keep up, especially in “loud” speaker mode.As a result, more high-end phones offer stereo as an additional feature

Cirrus Logic: Why smart power audio amplifiers are increasingly important for smartphones

There seems to be no end to what people consume on smartphones, tablets or other portable devices. As smartphone screens become larger, brighter, and provide a better overall visual experience, consumers are experiencing mobile content in entirely new ways, not just through headphones. It’s common for friends to get together and turn their phones sideways to watch videos using the phone’s external speakers, sharing the experience of watching and listening. Many phones have gotten larger screen sizes over the years, but the audio experience doesn’t always keep up, especially in “loud” speaker mode. As a result, more high-end phones offer stereo as an additional feature, usually with tiny speakers at the top and bottom. Now, when users look at their stereo-enhanced phone from the side (i.e. landscape view), they will find a speaker on both sides to help create a better “stereo” listening experience.

The trend towards stereo audio in smartphones and other audio playback devices shows that audio amplifiers play an especially important role in smartphone design. As a result, audio amplifiers have seen substantial growth in both capacity and technology (see Figure 1 below).According to SAR Insight & Consulting Audio Power Amplifier Market Growth Report1 : “Compared to 2010, the market shipments of audio amplifiers increased threefold in 2018, not only because of the increase in shipments of audio playback devices, but also the number of channels per device.” The report also noted that, Stereo speakers have been widely used in the high-end smartphone market priced above $550, especially since the introduction of stereo for iPhone® 7 mobile digital devices in 2016. Since then, many other flagship smartphones have also adopted stereo speakers in their products. The analyst firm also expects stereo to expand to mid-range phones priced between $200 and $500, with an estimated nearly 600 million amplifiers used in the mid-range market in 2018, which is expected to increase to nearly 700 million by 2023.

Cirrus Logic: Why smart power audio amplifiers are increasingly important for smartphones

Figure 1: Global Market Overview of Standalone Speaker Amplifiers by End Market

(Source: Q1 2019 report released by SAR Insight & Consulting)

The growing importance of boost audio amplifiers

However, the widespread trend of including stereo in smartphones does not necessarily ensure a high-quality audio experience. To this end, the miniature speakers should also be equipped with a smart boost audio amplifier that allows the speakers to reach their maximum loudness while protecting them from damage. Smartphone audio designers should use high-voltage audio amplifiers, speaker-monitoring analog-to-digital converters (ADCs), and advanced algorithms that keep tiny speakers in safe operation, ensuring better, louder, and clearer audio sound. Also, two speakers usually means two amplifiers. So size, efficiency, battery current management and audio performance are all twice as important. So, as smartphones move toward stereo, audio amplifiers that weren’t there before play an even more important role.

Below is a checklist of designs to ensure the smart boost audio amplifier works at its best.

Size – Board space is always a consideration when incorporating various features into a portable device, and one option is to place two miniature speakers on the top and bottom of the phone. Audio amplifiers must be smaller and more integrated, especially now that there are two. To address the size issue, Cirrus Logic used 55nm technology to design its latest CS35L41 smart boost amplifier with DSP, making it easier for OEMs to adopt dual speaker designs without sacrificing the space required for other new features.

Efficiency – SAR Insight research also confirms that Class D has almost replaced Class AB amplifiers in many markets due to improved efficiency in Class D audio amplifiers. Higher power 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 the supply with higher efficiency than Class-G, while an additional battery management system predictably adapts to changing audio, speaker and Battery condition to regulate battery current and save power. This underscores the evolving technology and “enhancement” role of boost audio amplifiers, as shown in Figure 2.

Cirrus Logic: Why smart power audio amplifiers are increasingly important for smartphones

Figure 2: Class G and H rail voltage vs time

Speaker Protection – According to SAR Insight & Consulting, the use of speaker protection algorithms with embedded DSPs in amplifiers has become increasingly common in many applications such as smartphones where small speakers are used. These algorithms allow for higher output without damaging the speakers. For example, the Cirrus Logic audio amplifier achieves over 5 watts of power in a 1 watt speaker. This new boosted audio amplifier delivers the power needed for higher excursions to generate louder, clearer audio, especially on speakerphones, without damaging the ultra-compact tiny speakers. The SAR Insight report further states, “The use of speaker protection in mid-range smartphones has grown rapidly since 2013, as OEMs look to maximize speaker performance and combine it with other enhancements such as high-end codecs. , to achieve a differentiated design.”

Audio Enhancement – Even with all of these features, not all audio enhancements are the same. To produce better clarity and enhanced stereo audio to match those vivid, larger screens and visual content, advanced algorithms in the integrated DSP should also address audio design issues such as equalization, compression and psychoacoustic enhancement to fine-tune the audio playback.

Smartphones and other mobile devices are fast becoming the primary platform for streaming and enjoying content as users abandon traditional cable or satellite TV and want to see more unrestricted content. To accompany a clearer, brighter visual experience, more and more phones are moving from mono or mono audio designs to two-channel stereo for a better listening experience. As this trend continues, the need for smart power amplifiers becomes increasingly important. This means that smartphone OEMs are not only looking for space savings in headsets and hands-free modes, but also for improved energy efficiency and audio clarity to differentiate their products from the competition.

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