DALLAS Texas Instruments Inc. here this week announced an all-digital amplifier chip solution.
The company's TDAA chip set provides a totally digital signal processing chain from line-level input to high-power output. (Apogee Technology unveiled a pulse-width modulator, the front end to a digital amplifier chain, at November's Comdex computer show).
TI's chip set comprises the TAS5000 and two TAS5100s. The TAS5000 is a pulse-width modulator that converts a Sony-Philips Digital Interface (S/PDIF) input or USB data stream into a pulse stream that can be amplified by a digital class-D amplifier, consisting of two TAS5100 H-bridges. The TAS5000 digital modulator takes I2S pulse code modulation (PCM) data a 16- to 24-bit data stream, sampled at 44.1- to 96- kHz rates transforms it into a pulse-width modulated stream to drive the amplifiers and outputs (through the stereo TAS5100 H-bridges) 30 watts per channel into 4-ohm loads.
In addition to high efficiency, the chip set touts audiophile fidelity, a rare feature in low-cost devices, said Niels Anderskouv, director of TI's digital audio development effort. The fidelity of the True Digital Audio Amplification (TDAA) chain (of which the TAS5xxx chip set is a part) follows an eight-year development effort at Toccata Technologies, which TI acquired earlier this year (see March 16 story). The earliest development efforts going back to Danish University research in 1993 relied on pulse-density modulation (a digital amplifier technology still used by companies like Sharp and Tripath Technologies), said Anderskouv. But this technology did not embody the combination of fidelity and efficiency that Toccata was looking for, and development switched to pulse-width modulation. The prototype PWM amplifier was completed in 1995.
Toccata Technology was founded in 1997 in Copenhagen. Its "equibit" technology what Anderskouv believes was the world's first digital audio power amplifier was marketed by TacT. This digital amplifier technology was licensed to TI in the first quarter of 1999 to implement these modulation techniques in semiconductors. TI introduced one of the industry's first USB interfaces for digital audio processing in November of 1999, and at the same time announced its digital audio processor (a DSP-based active equalizer) for PC audio systems. TI acquired Toccata in March.
Though joint TI-Toccata demonstrations at the Consumer Electronics Show in January convinced many analysts that semiconductor amplifiers based on Toccata's digital audio techniques could compete in sound quality with the best high-end linear systems, it would also be another year before the perfected semiconductor was ready for full production. The choice of 30-W output for the first TAS5xxx devices was strategic: Some 90 percent of the amplifier market is below 50 W, said Anderskouv. But additional amplifier devices that will build 200-W amplifiers for home theater systems are being developed. Also in the works for early 2001 is a digital audio device with a 1394 interface.
Besides targeting home and PC audio, the digital audio technology will promote sound quality in other consumer entertainment apps like digital headsets, home theater, car audio systems and traditional mini-stereo systems.
TI is prolific in other parts of the chain, Anderskouv said. Dedicated digital audio processors like the TAS300x devices, for example, perform speaker equalization and dynamic range compression with volume, bass and treble. Early next year, TI plans to offer a 24-bit audio processor (the TAS3002) that performs parametric equalization, treble, bass and volume control.