Bristol, UK—The Class D amplifier is the topology of choice in many audio applications because of its high efficiency, in the 80 to 90% (or higher) range at its higher-power levels. But this efficiency drops off in the standard Class D approach.
Relative newcomer Audium Semiconductor Ltd claims to have overcome this drawback, with a novel, proprietary design which maintains efficiency across all power levels. Their AS1001 100W mono amplifier, targeted at embedded applications such as wireless speakers, home theaters, and portable speakers, minimizes the difficulties of dealing with the relatively high peak-to-average-power ratio (PAPR) characteristic of music applications.
Although the details of the Audium approach are confidential, it does not use pulse width modulation (PWM) but instead uses a low bit rate scheme, along with dynamic adjusting of supply rail, adding rails as needed. The vendor says that for a 1-kHz sine wave with an 8-ohm load, efficiency is as good as it would be for a well-designed Class D unit, even at modest, normal listening levels of 73 dBC sound pressure level (SPL) at one meter, with a speaker sensitivity of 89 dBC/W at one meter; power dissipation is 60 mW when delivering 25 mW into this load.
Input format to this 64-lead QFN IC is via an I2S interface, supporting 32-to-48 kHz rates, at 16 bits per channel. The IC operates from 0.8 to 1.8 rail for the amplifier (compatible with Ni-MH secondary cells as well as basic alkaline primary cells), in addition to a 3.3V source for the logic circuitry. Users can set volume, filter parameters and equalization (12 choices are available), among other factors.—Bill Schweber
Price and availability: The Audium AS1001 is sampling now, and priced at $8 each in 100-piece lots.
For more information: Audium Semiconductor, www.audiumsemi.com.
