Korea: Audio ICs fit perfectly in portable multimedia devices

High-integrated analog ICs, also known as audio subsystems, are popular these days as the market for mobile phone, MP3 player, portable multimedia player (PMP), navigation, and portable game player is gradually expanding. The main analog IC vendors in Korea offer a variety of product families ranging from low-end to high-end ones, depending on the demand from manufacturers.



The most important requirements of audio ICs in portable devices are (1) the ability of prolonging the lifespan of the device through appropriate output, and (2) ensuring great, noise-free audio quality. As for mobile phones, it is important to remove the audio noise caused by the RF. This is why audio subsystems have become popular.

A BIT OF HISTORY

"It was three years ago when audio subsystems were introduced for the first time. As mobile phones have become slimmer, the popularity of audio subsystems is getting higher," said H. S. Son, a product applications manager at National Semiconductor. "Their performance is expected to be excellent since multi-functions have been added to new applications such as GPS and WiBro."



"Product families of audio subsystems, where main audio parts are integrated into one package, vary depending on purpose and performance," Son added. "Our LM4946 boomer, a Class D audio subsystem, supports the I2C digital interface for the reception of digital broadcasting and does not use output capacitor-less (OCL), which is a cause of noises. The LM4946 is the main digital audio subsystem that integrates a mono amplifier, a stereo headphone amplifier, and RF suppression circuits (for preventing noises), and enables programmable 3D sounds."



IDEAL SIZE

As multimedia devices are getting slimmer and miniaturized, the demand for one-chip solutions has also increased. In a high-integrated audio IC, the operational amplifier, DAC, ADC, codecs, and switches are all integrated into the same chip. Its noise, power consumption, and accuracy have also improved greatly—making it ideal for lowpower applications that require high SNR, such as mobile phones and portable audio devices.



Typically, the SNR ranges from 80dB to 95dB and the amplifier output ranges from 500mW at 3.2V to 3.5V. (Some time ago, Linear Technology launched a super lowpower operational amplifier of less than 1µA.) Some applications use a DC/DC converter to obtain higher output.



Gi-tae Kim, CEO and President of Wolfson Microelectronics Korea, said, "As prices of multimedia processors have become lower, high-performance audio ICs which used to be for high-end applications only are now being installed into regular portable audio devices. This trend is expected to increase."



AMPLIFIFER CLASSES

The two amplifier classes that are widely used in portable multimedia devices are Class AB and Class D. Class AB audio amplifiers are typically used for regular mobile phones.



Meanwhile, Class D audio amplifiers are used for mobile phones that demand more efficient power consumption features. Although Class D is more efficient than Class AB, the latter ensures excellent sound quality, making it more widely used.



Wolfson Microelectronics plc Korea will launch a first-of-its-kind internal audio codec that will enable compatibility between Class AB and Class D audio amplifiers. The new codec will make the most of the advantages of Class AB and Class D audio amplifiers.