"Portable" and "audio" have been synonymous since the first transistor radio became commercially available in the 1950s. But it's the end of 2008 and chip makers still strive to deliver high-performance audio at battery-friendly power levels, an effort likely to last as long as portable electronics dominate our lives, or at least our teenagers' lives.
Chip vendors, particularly those in the analog market, are developing codecs and subsystems to help portable-electronics engineers meet this design challenge. And lately, it seems as though the chip choices are boundless.
Maxim Integrated Products is touting its latest device in this arena as the industry's smallest audio subsystem. The MAX9877 combines a high-efficiency, high-power, mono Class D speaker amplifier; a DirectDrive stereo headphone amplifier; and a low-noise, bypass analog switch. In addition to this integration, the MAX9877 employs Maxim's third-generation, ultra-low-EMI, Class D amplifier technology to provide Class A/B audio performance with Class D efficiency.
Sounds nice: Chip vendors hear the call for high-quality audio at low battery levels in portables
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The MAX9877 provides the industry's highest output power from a lithium-ion battery, according to Maxim, making it well-suited for cell phones, portable media players and other applications that require high audio quality, output power and efficiency. It delivers 725 mW of output power from a 3.7-V supply into an 8-ohm load with 85 percent (maximum) efficiency. Maxim's patented DirectDrive architecture produces a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors. To further save cost and space, the MAX9877 uses Maxim's active-emissions limiting and patented spread-spectrum modulation, which significantly reduce EMI and eliminate the output filters typically required by Class D amplifiers.
Cirrus Logic has developed a portable audio codec, dubbed the CS42L55, that consumes 5.1 mW of quiescent power in playback mode and features a bimodal, patent-pending Class H technology. According to Cirrus, the CS42L55 reduces power consumption by nearly 50 percent compared with the Class A/B amplification found in today's portable applications. The CS42L55 features an ultra-small 5 mm x 5-mm footprint, and a height of 0.45 mm.
Based on 24-bit advanced multibit Delta-Sigma technology, the CS42L55 operates from a single 1.8-V or 2.5-V power supply and can deliver 1-VRMS line output from a 1.8-V supply. When driving headphones from the same supply, it can deliver 17 mW per channel of high-quality, 96-dB dynamic-range audio. The CS42L55 also provides a 2:1 stereo input multiplexer and a USB master clock input and supports sample rates up to 48 kHz.