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Tiny digital chip delivers up to 20 W audio output


July 19, 2013

STMicrosystem's new stereo digital audio amplifier

STMicrosystem's new stereo digital audio amplifier

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If you can find one, the new STA333IS digital audio chip and power amplifier from STMicroelectronics (STM) offers a quick and easy solution for converting digital audio into a 10 watt/channel stereo for anything from a boom box to a backyard sound system. Don't misunderstand, they currently are at distributors, selling for about one US dollar apiece. The problem is literally finding the chips. At about one-eighth the volume of a grain of rice and weighing only a few milligrams, drop one on a carpet and its gone for good.

Industry-leading output power density of about 7 watts/cubic millimeter makes the STA333IS the smallest digital audio sound system in its class. It can accept any possible format of serial digital audio input, including the I2S standard. When restricted to 1-2 watts per channel, the system is arguably audiophile grade, with total harmonic distortion (THD) of about 0.05 percent, dynamic range of 100 dB, and crosstalk between channels reduced by 80 dB. Unfortunately, at ten watts/channel output, the THD spec is a full ten percent.

The audio signal is manipulated digitally, depending mainly on STM's proprietary fully flexible amplification (FFX) for digital audio processing. Two channels of FFX processing are provided, one for each stereo channel. In addition to the usual static and dynamic volume, balance, and spectral adjustments, the processing can also adjust the signal so as to counteract, for example, nonlinear response and/or distorted output resulting from the speaker design. This same principle allowed STM to include advanced modes for reducing AM radio interference.

Once the digital audio signal is fully massaged, it must be converted into an analog audio signal sufficiently powerful to drive a set of high-quality speakers. This conversion is carried out by pulse width modulation (PWM) techniques. As a result, the "'audio amplifier" that also performs digital to analog conversion is simply a set of MOSFET switches whose output is controlled by the digital audio signal. This not only results in simple circuitry, but also allows the STA333IS to operate at over 90 percent efficiency.

An evaluation board built around the STA333IS chip, showing how few extra components are r...
Schematic of the evaluation board shown above (Image: STMicrosystems)

Little of the functionality provided by the STA333IS is terribly new. What is new is being able to integrate that functionality onto a single tiny chip. Only 14 small components and a power supply need be added to the 333IS to release that functionality on a digital audio signal – a remarkably small number. While other manufacturers are also moving in this direction, the introduction of the STA333IS provides STM with a tactical advantage in what is a massively dynamic marketplace.

Source: STMicroelectronics

About the Author
Brian Dodson From an early age Brian wanted to become a scientist. He did, earning a Ph.D. in physics and embarking on an R&D career which has recently broken the 40th anniversary. What he didn't expect was that along the way he would become a patent agent, a rocket scientist, a gourmet cook, a biotech entrepreneur, an opera tenor and a science writer.   All articles by Brian Dodson

I don't know about it's power requirements (ie size of batteries), but it seems to me with 10% THD it'd add just a touch of bite.. it could fit right inside a guitar cord and you could just plug your guitar into a speaker directly, and voila! Instant practice amp.

19th July, 2013 @ 04:45 am PDT

Headphone amp?

Tom Swift
19th July, 2013 @ 07:53 am PDT

Tom my thoughts exactly! :) and SGdeluxedoc I think that would be a fine idea, the problem would be finding the power source for the chip.... Hmmm an inline Supercapacitor you could charge could do the trick. :) like this one

Jesse Gunn
19th July, 2013 @ 11:11 am PDT

Killer pre-amp?

Cecil Hutchins
19th July, 2013 @ 11:13 am PDT

sounds good for a phone amp sound quality is important loud and garbled doesn't help.

19th July, 2013 @ 02:29 pm PDT

As for a guitar or headphone amp, sorry.

Serial digital audio input, no analog.

David Bell
19th July, 2013 @ 02:53 pm PDT

I don't know how they are counting, but any way I count it it appears to be more than 14 additional components on the example circuit and board.

20th July, 2013 @ 08:38 am PDT

I was thinking along the lines of a hearing aid. A small button pinned to a shirt and then bluetooth to a small hearing aid in the ear.

S Michael
20th July, 2013 @ 06:53 pm PDT
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