NXP Semiconductors develops new algorithm to boost power of micro speakers

NXP Semiconductors has announced that it has developed a new embedded algorithm for audio systems that boosts the output power of micro speakers by over 5 times, improving the sound quality of mobile devices. By driving over 2.6 watts RMS into micro speakers that have previously been limited to 0.5 W, the NXP TFA9887 IC will give mobile phones, portable music players, and tablets much louder sound, deeper bass, and higher sound quality – without risking speaker damage. With a combination of safety features including adaptive excursion control and real-time temperature protection, the TFA9887 monitors speakers through a current-sensing amplifier and enables safe operation while working at near peak output at all times.

“Digital natives have come of age taking poor mobile sound quality for granted. As speakers have become smaller, the quiet, tinny sound we’ve come to associate with mobile devices has got even worse,” said Shawn Scarlett, director of marketing, mobile audio product line, NXP Semiconductors.“Our new audio system transforms the listening experience, enabling louder, richer sound quality from virtually any mobile device. The improvement is so striking that consumers, handset makers and operators will immediately hear the difference.”

Speaker makers have to balance competing demands for good sound, small size and reliability. As micro speakers have shrunk, phone, media player and tablet designers have been forced to limit output power and sound quality. Amplifiers could easily deliver enough power to destroy the speaker at one frequency, while under-powering it at others. Until now, it has been impossible for system designers to know for sure when it was safe to apply extra power. The rule has therefore been to cut out bass frequencies and limit output power to avoid blowing the speaker – a common cause of failures in mobiles.

NXP has developed a new algorithm to boost micro speaker power

By incorporating circuits that monitor speaker performance and prevent damage, the NXP TFA9887 IC allows designers to break this rule, as per an official statement by the company. Adaptive excursion control measures the actual excursion of the speaker membrane to ensure that it never exceeds its rated limit. Real-time temperature protection measures the voice-coil temperature directly to prevent thermal damage.

As the speaker is fully protected, the system can deliver significant levels of extra power to make the sound louder and better than before. A clip avoidance algorithm monitors audio performance and prevents clipping, even when the power supply begins to sag. Bandwidth extension increases the low frequency response well below speaker resonance. And a DC-to-DC boost converter maximises audio headroom from any supply level despite battery undervoltage. The TFA9887 automatically adapts to any changes in the speaker – including ageing, damage to the enclosure, and blocked speaker ports.

The entire system is integrated into a single chip with digital interfaces for portable devices. The IC incorporates NXP’s CoolFlux audio DSP, and a class-D amplifier with current sensing. The embedded algorithms require no separate licensing. Additional tools allow designers to customise audio sound quality and choose how to optimise mobile device performance.