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Audio PA betters Class-D for battery-driven speakers

 

Audium Semiconductor is a recently founded fabless chip-maker that has designed a power-amplifier chip offering very high efficiency at normal listening levels. It is targeting designers of products such as wireless speakers, home-theatre surroundsound speakers and battery-powered travel speakers. For applications such as surroundsound speakers, Audium offers the concept of a unit that will have both a wireless receiver and a power amplifier operating.

Normal Class-D designs, the company says, offer high effi ciency at full output power but have signifi cant quiescent current that limits their low-output-power effi ciency. Normal domestic levels—which Audium defi nes as a 73-dBC SPL (sound-pressure level) at a distance of 1m, with a speaker sensitivity of 89 dBC/W at 1m—equate to low levels of electrical power. Audio content typically has a high peak-to-average ratio in its amplitude, the company says, and its technology exploits this.

Its chips accept standard digital audioprogramme streams and use an effi cient, pulse-frequency-modulation scheme to generate a digitally modulated output to drive a loudspeaker. At low signal amplitudes, the chip runs from a low-voltage rail; at the same time, a dc/dc converter in the design generates a higher voltage rail and stores charge at that higher voltage in external capacitors. When the audio-programme material contains a loud peak, the chip drives its output devices from the higher voltage reserve, enabling it to deliver “up to 100W peak”, according to the company, with 20 times the effi ciency of a Class-D design. With typical audioprogramme material, a wireless speaker will run for three hours per day for 10 months on four C-size 1.5V cells, Audium claims.

According to Audium’s Chief Commercial Offi cer Huw Davies, “We make no claims to be “Hi-Fi”; but harmonic distortion is low at under 1%.” Coded AS1001, Audium’s fi rst product comes in a 64-pin QFN package and operates directly from a 0.8-to-1.8V supply. Samples are available now; pricing is from $8 (1000).

Audium Semiconductor, www.audium.com