Mobile audio algorithm enables over five times the power to micro speakers

July 17, 2012 // By Paul Buckley
NXP Semiconductors has developed a revolutionary embedded algorithm in a new audio system that the company claims boosts the output power of micro speakers by more than five times while improving the sound quality of mobile devices.

By driving over 2.6 W RMS into micro speakers that have previously been limited to 0.5 W, the TFA9887 IC gives mobile phones, portable music players and tablets much louder sound, deeper bass, and higher sound quality – without risking speaker damage. Applying 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.

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.

By incorporating circuits that monitor speaker performance and prevent damage, the TFA9887 allows designers to break this rule. 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.

Because the speaker is fully protected, the system can deliver significant levels of extra power to make the sound louder and better than before. The TFA9887 optimizes the audio signal based on the movement of the speaker, something no other system is capable of, using the full capabilities of the speaker without pushing beyond the limits. An advanced 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 an intelligent DC-to-DC boost converter