26 AUTOMOTIVE AUDIO SYSTEMS https://www.ti.com/ Issue 2 2024 Power Electronics Europe www.power-mag.com Shrinking automotive audio system designs with Class-D amplifier 1L modulation Sophisticated digital processing and analog semiconductors are helping audio designers create new ways to deliver an immersive audio experience to meet consumer demand for enhanced audio technologies – on portable speakers, laptops, sound bars and in automotive sound systems. Today’s automotive audio systems are far more sophisticated than the vacuum tube-powered amplifiers used in the very first single-speaker car radios. Some new car models have two dozen or more speakers throughout the vehicle. The progression from these first systems to the immersive, high-quality audio systems available today centers on four design trends that can deliver better audio in vehicles: size, weight, cost and audio quality. These trends are well-known across the automotive audio market. However, the real challenge is how to shrink a solution and its cost while maintaining quality audio performance. Pushing audio amplifier designs further For several years, automotive audio systems used Class-AB audio amplifiers to deliver sound to car speakers. In past years, there’s been a trend to switch from ClassAB amplifiers to Class-D amplifiers. Class-D amps help designers achieve higher power efficiency, as well as reduced thermal dissipation and system weight targets. Design engineers familiar with Class-D automotive amplifiers know that they require two inductor-capacitor (LC) filters per channel of audio to filter highfrequency switching noise. To shrink the size of the LC filters, TI developed audio amplifiers to support up to 2.1MHz switching, enabling the use of significantly smaller and cheaper inductors. Figure 1 compares this size evolution of the inductors from 400kHz to 2.1MHz. Now, TI is taking the next step to further reduce LC filter size with an audio amplifier integrating our proprietary one-inductor (1L) modulation technology. This technology maintains Class-D performance, while cutting the number of inductors per channel by half, which leads to 50% less inductor cost and a solution up to 50% smaller and lighter. The end benefits include simplified audio designs and increased efficiency. 1L modulation technology in action Our 1L modulation technology halves the inductor count in the LC filters. Now imagine a carmaker whose vehicle trim line includes a high-end model with a sound system that requires 32 audio channels. For every channel of audio, there is a speaker, and every speaker has two connectors: positive and negative. For an amplifier only supporting BD or one-sided pulse-width (1SPW) modulation, each lead requires an LC filter, totaling 64 inductors. With a 1L modulation amplifier, you only need one LC filter per channel of audio, reducing the number of inductors to 32. Mark Ritchey, Product Marketing Engineer at Texas Instruments
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