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Audio subsystem integrates smart phone, VoIP phone functions

Posted: 11 Jan 2006 ?? ?Print Version ?Bookmark and Share

Keywords:audio subsystem? speaker driver? National Semiconductor? VoIP?

Class D speaker driver

The audio subsystem with a mono Class D speaker driver from National Semiconductor Corp. integrates all the analog and digital audio functions needed for smart phones and VoIP phones. A member of the Boomer audio power amplifier family, the LM4935 subsystem provides high-quality output power with a minimal number of external components.

"Smart phones bring the convergence of PDA functionality, wireless connectivity and, increasingly, consumer audio to one full-featured device," said Mike Polacek, VP of National's audio products group. "The LM4935 allows handset designers to add the new audio features consumers demand. Its integration drives design simplicity and takes up a minimum amount of board space."

Touted by the company as the industry's smallest, the LM4935 audio subsystem includes multiple digital and analog inputs and outputs. Operating on supplies ranging from 1.8V to 5.5V, the LM4935 combines several features: a Class D speaker amplifier delivering 570mW into an 8? load; a stereo headphone amplifier that supports output capacitor-less or AC-coupled operation delivering 30mW per channel into a 32? load; a mono earpiece amplifier delivering 30mW into a 32? load; and a line output for an external-powered handsfree speaker providing filter-less Class D stereo speaker capability. Other features include a successive approximation register analog-to-digital converter for system monitoring and a high-fidelity digital-to-analog converter.

The LM4935's bi-directional I2S digital interface with PCM capability transmits any audio file or voice data transmission back and forth from the baseband ASIC or processor to the analog outputs. The subsystem also features a read/write I2C compatible digital interface.

National added that the LM4935 gives engineers design flexibility in arranging analog inputs through a sophisticated switching/mixing circuitry, eliminating the need for external audio switches and mixing components. Two analog inputs allow the LM4935 to accept a stereo signal from an FM radio or operate as two separate mono inputs that can accept other analog input signals. Additional analog inputs allow for differential mono input and output from a GSM, CDMA or other cellphone radio module as well as a baseband ASIC. Two additional inputs support internal and external microphone capability.

Available in a 49-bump micro SMDxt package, the LM4935 is priced at $3.95 each in 1,000-unit quantities.

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