News and New Products

Class D amplifiers target space-constrained apps

By Jeff Berman, News Editor -- EDN, 3/3/2005

Analog Devices recently rolled out a line of amplifiers for the automotive and flat-panel-TV markets, which, it claims, combine space- and heat-savings benefits of Class D amplification with Analog's audio-signal-processing technology. The company expects the audio technology to improve sound quality and audio fidelity and to decrease EMI.

According to Bill Slattery, Analog's product-line manager for its digital-audio-product group, linear amplifiers are still leading the way when it comes to quality and performance. Class D amplifiers have their own inherent strengths, however, according to Slattery. "In a linear world, Class D lets you receive a linearlike performance in a smaller space," he says, adding that Class D amps' performance is challenging linear for sleek, small systems lacking the room for bulky amps. "These amps have a more compact design [than linear amplifiers], and … Class D is back to the audiophile performance [that] linear amps have," he says.

The new amplifiers, AD1990, AD1992, AD1994, and AD1996, deliver audiophile sound quality with less than 0.0005% total harmonic distortion plus noise, as much as 40W of output power per channel with at least a 30% heat reduction, and a dynamic range greater than 101 dB.

The amps comprise power-stage-design capability, advanced sigma-delta modulator, closed-loop-feedback topology, and advanced mixed-signal and power and digital CMOS processes."Using sigma in a closed loop gives the best performance, and closed loop is important because it gives nonlinearity in output," Slattery says. "In the past, many Class Ds have used an open loop, which is self-limiting after a certain point." These amplifiers are instrumental in fixing design issues in HDTV and home-theater systems with lower EMI, resulting in lowered interference with other electronic equipment. The amplifiers are currently available for sampling, and full production quantities will be available in April. Sample prices range from $2.90 to $6.72 (1000).

Analog Devices, www.analog.com.