REVIEW: Reference design slated to ease diffused IR stereo audio

STMicroelectronics and Infra-Com Develop Wireless Digital Audio Reference Design for High-Quality Home Entertainment Systems

A cost-effective reference design embedding ST and Infra-Com chips featuring non-line-of-sight, high-bit-rate infrared communications and, exploiting the all-digital audio processing and power amplification capabilities of ST's Sound Terminal family

Geneva and Netanya—STMicroelectronics (STM), a world leader in digital audio ICs, and Infra-Com Ltd., a world leader in short range diffused infrared (DIR) wireless communication ICs, announces a complete reference design for a high-bit-rate wireless audio solution intended for consumer electronic products such as home theater systems, surround-sound and gaming speakers, DTV speakers, as well as portable music and aftermarket accessories. The Drum and Violin designs combine Infra-Com's receiver side IrGate IC with the all-digital class D power amplifier and signal processor from ST's Sound Terminal family, creating a complete high-quality remote audio amplification system.

Audio signals using Infra-Com's IrGate wireless infrared protocol are processed by an IrGT801ADR Modem and Interface IC, which receives data from the infrared sensors in the optical/analog front-end via an LVDS (Low Voltage Differential Signaling) interface and drives the ST's full digital amplifier through an I2S (Inter-IC Sound) serial digital audio interface.

The Drum solution embeds ST's STA326, a fully-digital IC amplifier that is able to deliver 2x60W of audio power into 8 ohm loudspeakers. It provides true hi-fi audio quality, with an uncompressed 24-bit 48kHz PCM (Pulse Code Modulation) wireless link, and almost zero latency for perfect lip-sync. Latency is just 150 microseconds compared to typically more than 7ms for competitive RF-based solutions. Amplifier efficiency is up to 92%—among the highest in the market—allowing a compact heatsink and power supply to be used in the overall application. The amplifier enjoys full built-in over-current and over-temperature protection capabilities, and the all-digital audio stream maintains full audio quality and 100dB signal to noise ratio (SNR) and dynamic range.

The Violin solution embeds ST's STA333ML, a fully-digital micro-less IC amplifier that is able to deliver 2x20W without the need of external heatsink. The STA333ML retains the highest digital audio quality without adding software development efforts.

DIR enables optical communication without the need for line-of-sight between the transmitting and receiving nodes. Unlike a direct infrared signal—which emits light in a narrow beam—a diffused infrared device floods the room with the infrared emissions and utilizes natural reflections from the ceiling, walls, floor and other surfaces to maintain robust high bit rate communications, unaffected by obstructions or by moving people within the enclosure. The link effectively behaves similarly to a radio signal within its operating space, but with no possibility of being affected by, or generating, radio frequency interference (RFI); it is also insensitive to remote control signals, and cannot be overheard in an adjacent room. Additionally DIR is a worldwide unregulated technology operating at 870nm.

The STA326 single-chip audio system integrates digital audio processing, digital amplifier control and a DDX digital power output stage. It can be configured easily via digital control to operate in one of several different output modes, and offers a full range of processing and equalization options, including up to 4 programmable 28-bit biquads per channel, and bass and treble tone control. The device is one of a range of single-chip and single-package audio products in ST's Sound Terminal family; other amplifiers in the family can be used with the Drum design to satisfy different audio power requirements, from 2x1W up to 2x80W.

“The Drum is the first of a set of complete and easy-to-use turnkey designs for manufacturers of remote audio products, combining high quality amplification with the user convenience of diffused infrared technology,” said Andrea Onetti, General Manager of the Audio Division within ST's Home Entertainment and Display Group. “The Drum and similar designs will complement other interfaces such as Bluetooth 2.0 EDR (Enhanced Data Rate), WiFi and UWB (Ultra-WideBand) in the Sound Terminal family, and we look forward to introducing a single-package DIR and digital amplification solution in the future.”

The Drum and Violin reference designs are available now as the M2C_IrGT801ADR_STA326 and M2C_IrGT801ADR_STA333ML modules, respectively, for evaluation and product development.

This joint product announcement from Infra-Com Ltd . in Israel, and STMicroelectronics (STM), is enticingly exciting. Unfortunately, although the joint press statement (on the left) claims the companies are offering two “cost-effective reference designs,” little or no details are available about the designs themselves. My call to STM resulted in no further information. Worse, Infra-Com chose to not return my telephone calls at all. Hopefully that's not an indication of the support the company might provide.

Fortunately we do have images of Infra-Com's transmitter board and the STM reference designs (the Drum is shown immediately below), so there's hope that these items do exist. Again, although the companies insist they're cost-effective, pricing apparently has yet to be established or released for either the low-power Violin or the ear-smashing Drum. Yuk.

In any case, there is technical information available on the reference design sub-components. As the press release states, audio is transmitted using Infra-Com's IrGate infrared (IR) protocol. This is processed by the company's IrGT801ADR chip.

Digital Reception

The IrGT801ADR acts as a digital baseband demodulator and interface. It's also designed to work in conjunction with Infra-Com's mating IrGT801AR , an analog receiver, for 2-way transmitted/received audio. The IrGT801ADR handshakes with the IrGT801AR through two pairs of LVDS (low voltage differential signal) lines, serving as a digital processor between an application's digital interface and the IrGT801AR analog receiver IC.

I digress. Using the reference digital audio systems such as DVDs, MP3 players, active speakers, and digital TV-sound, could be made wireless using Infra-Com's short-range DIR (diffused IR) system. Thanks to the IrGT801ADR's audio interface, you can use standard serial digital audio linking.

The IrGT801ADR, packaged as a 48-pin 9 x 9-mm TQFP (thin quad flat pack), is essentially a DSP. Its internal DSP engine handles de-modulation, FEC (forward error correction) decoding, and supporting up to four selectable digital audio channels for driving four loudspeaker channels.

The device also provides automatic support of 44.1-kHz and 48-kHz sampled audio. Additionally, the IrGT801ADR silicon features audio sample error concealment, muting, and speaker shut-down capabilities. Clock and data recovery is accomplished using a digital PLL (phase locked loop).

Loudspeaker Shut-Down

The IrGT801ADR's speaker shut-down function is interesting. In operation, if a wireless connection remains inactive for a continuous three minutes, the device detects this and provides a hardware output to shut down an audio system's loudspeaker electronics. When the IrGT801ADR chip detects incoming IR frames again, it permits normal speaker operation. In a battery powered product, this can save idling power.

For its part in an audio system, STM's Drum design uses the company's STA326 digital amplifier chip. The STA326, with its built-in heat slug, integrates digital audio processing, digital amplifier control, and the DDX Power Output Stage mentioned in the press release.

The STA326 can be digitally configured to operate in several output modes, and can deliver two 60-W channels of full-bridge output power into 8-ohm loads (operating at 32-V) for stereo. The device can also be configured as a single paralleled full-bridge. In that case it can deliver a whopping 120-W of audio output.

Programmable Processing

On the digital side, the STA326 provides up to four programmable 28-bit bi-quads (equalization, or EQ) per channel, as well as bass/treble tone control. So-called automodes are also available. Automodes include loudness, preset volume curves, and preset EQ settings, to name a few. The device's serial audio data input interface accepts all formats, including I2S (Inter-IC Sound).

In addition to the Drum, STM offers the lower power Violin reference design. It uses the company's STA333ML amplifier to deliver two 20-W channels of digital audio streaming. As you can see in this image, there are no heat spreaders on the substrate, nor heatsinks.

As a single chip, the STA333ML requires no external microcontroller or heatsink. Sidestepping the need for a controller, the STA333ML looks like just the ticket for low cost applications.

The STA333ML also uses STM's 24-bit DDX Class-D modulator, mated with a low RDS ON DMOS output stage. The DMOS output is greater than 90-percent efficient. The STA333ML is also self-protected against thermal overload, over-current, shorts, and over-voltage. It also packs a mute enable function. If enabled, a zero-detect circuit examines each processing channel to see if 2048 consecutive zero value samples are received. If so, the channel is muted.

Click here for further data on the Infra-Com chip.

Click here for a STA326 datasheet (in Adobe Acrobat .PDF format).

Click here for a STA333ML datasheet (in Adobe Acrobat .PDF format).

For more details, contact STMicroelectronics, Inc., Lexington Corporate Center, 10 Maguire Rd., Bldg. 1, 3rd Floor, Lexington, Mass. 02421. Phone: 781-861-2650.

STMicroelectronics , 781-861-2650,

Contact Gilad Hoshen at Infra-Com Ltd., 18 Haplada St., Netanya, 42135 Israel. Phone: 972-9-8617297. Fax: 972-9-8820648. E-mail:

Infra-Com , 852-35190219,

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