Class-D amplifier revs up mobile sound quality

26th April 2016
Mick Elliott

To meet the demand for mobile devices offering top quality sound - without sacrificing power - Nanyang Technological University (NTU) has invented an ultra-high-quality Class-D amplifier. Created by NTU’s Division of Electrical and Electronics Engineering in Singapore, the ultra-high-quality chip can tolerate more 'noise' from other components in a device, which reduces distortion so the sound quality can be significantly improved.

In view of the high power-efficiency requirement, virtually all smart mobile devices today use Class-D amplifiers (CDAs) as the driver to the primary loudspeaker. 

An ideal Class-D amplifying stage has no distortion and no noise generation in the audible band - and provides close to 100% efficiency. However, in practice, CDAs have imperfections that generate distortion and noise.

To obtain high power efficiency without resorting to a high switching frequency, the team at NTU proposed a novel CDA design, which embodies an input-modulated carrier generator and a phase-error-free, pulse-width modulation (PWM) modulator.

During development, the NTU team used Brüel & Kjær’s PULSE system and Head and Torso Simulator (HATS) to ‘listen’ to the sound from a headset driven by a CDA and then measure the acoustical audio signal.

NTU senior research scientist Ge Tong explained: “This was essentially an integrated circuit design project. The development process started with the schematic design and simulation, followed by layout, parasitic extraction and post-layout simulations.”

The result of this project was unprecedented performance from the CDA. The pinhead-sized chip encompassing the novel CDA design ultimately means that the audio from smartphones will sound like it is coming from high-end stereos, while wireless headphone users will be able to enjoy a longer battery life. Future applications of the chip include audio amplifiers, car audio systems and televisions.


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