Digital Audio Amps Help Create Powerful, Compact Surround Sound Systems

A new technology, called Direct Digital Amplification (DDX), has been tapped to develop audio ICs for use in building powerful, compact surround sound systems, such as DVD home theater systems and mini component stereos. Developed by Apogee Technology and licensed exclusively to STMicroelectronics for developing dedicated audio ICs, DDX technology improves audio performance by eliminating the need for DACs; it also replaces conventional class AB audio amplifiers with more efficient switching amps, slashing power dissipation and the need for heatsinks to cool the chips. The technology was used here to partition the audio functions between a control processor and power amplifiers. The STA304A controller performs the basic DDX modulation function, plus other DSP-based signal functions. It converts two serial digital inputs in IIS or S/PDIF format into five channels of digital drive for the DDX power amplifiers. In addition, the chip performs surround sound processing plus volume, tone and balance control. Other functions such as equalization can be added by embedding additional hardware. Presently, two power amplifiers are available: the STA500 and STA505. They differ only in power rating, with the former delivering 2 x 30W or 60W in parallel mode and the latter delivering 2 x 50W or 100W in parallel mode. Both devices include, among other things, protection features against low or high supply voltages. STMICROELECTRONICS INC., Lexington, MA. (781) 861-2650.