Amps In 2006: Bargain Prices And Quieter Class D

ISSCC
Among the papers written for the International Solid State Circuits Conference (ISSCC) set for Feb. 4-8 in San Francisco, there is ample evidence that there's still no final resolution in the audio-amplifier wars between straight-analog Class AB output stages and PWM Class D amplifiers.

On the digital side, engineers from Texas Instruments and the Technical University of Denmark emphasize output power in "A 240W Monolithic Class D Audio Amplifier Output Stage." This chip contains two half bridges. When it's used in BTL configuration, the unclipped output power is 244 W into 4 ½. To the best of their knowledge, the authors say, this power level is unprecedented for monolithic output stages.

Also, TI offers "A Digital Input Controller for Audio Class-D Amplifier with 100W 0.004% THD+N and 113dB Dynamic Range." This controller architecture was designed for an audio Class D amplifier using a PWM switching scheme. Its digital input is provided by an integrated digital-to-analog converter (DAC) that has a special configuration to realize direct connection between the DAC and the feedback loop. It boasts 0.0018% total harmonic distortion plus noise (THD+N) at 10-W output power, 0.004% THD+N with 100-W output power, and 113-dB dynamic range.

On the linear side, Philips and STMicroelectronics are developing bipolar/CMOS/ DMOS (BCD) automotive audio power amplifiers, where a DMOS quad bridge forms the output stage.

Philips authors will present "Frequency Compensation of an SOI BCD Car Audio Power Amplifier." For frequency compensation, Philips researchers modified nested Miller compensation (NMC) using the parasitic gate-drain capacitance of the power transistors for most of the miller capacitance. Philips then built a 46-W amplifier using the scheme. With 10-W output, it achieved THD+N values of 0.005% at 1 kHz and 108-dB signal-to-noise ratio.