USB Audio DAC with On-chip DSP (9911)

MICRONAS makes the sound card redundant

Freiburg, September 1999 - The new USB audio controller from MICRONAS renders the use of sound cards unnecessary in future. Thanks to the integration on the chip of a DSP (96 MIPS, 48 MHz, pipelined), an EEPROM, a digital-to-analog converter, an operation amplifier, and a USB controller, this chip contains all that is required to balance a loudspeaker enclosure and to connect the speakers directly to the PC without a sound card. It means that retrieving music from the PC (e.g. via MP3) is possible in high quality and at low cost. This is the rationale for the target applications: digital loudspeakers, speakers in flat panel displays, speakers in VGA screens, home amplifiers, amplifiers in cars and in receivers.

The USB standard (Universal Serial Bus) offers the facility for hot plug-in, enabling peripherals to be connected directly to the PC without having to switch off and reconfigure the PC. So the user needs only to plug in the speakers and that's that. Thanks to HID implementation (HID stands for Human Interface
Device, the data required for which are stored in the EEPROM), the equipment is easy to operate. For example, the volume and other parameters are adjusted directly on the speaker. All settings are transferred to the PC via the bus and displayed on control panels.

The new USB audio controllers UAC 3552A offer the following additional features:

Digital signal processor: An equalizer enables the speaker chassis to be controlled simply without the need for external components. In future, therefore, one design can be used for different speaker types; it is only necessary to change the information for the configuration concerned.

• Sigma-delta DAC: The signal/noise ratio reaches 96 dB with harmonic distortion of the order of 0.01 per cent. Up to now, DACs in comparable modules reached 70 and, at best, 90 dB. The UAC 3552A therefore offers significantly better sound quality.
• Adaptive sample rate converter: Within the frequency range from 5 to 50 kHz the sample rate converter matches itself to the sampling rate of the system. Advantage: The listener is always provided with the optimum conversion regardless of the rates the system works with.
• Integrated EEPROM: Manufacturers of the speakers can store specific data in the integrated EEPROM to match their designs to the corresponding speakers. The programming takes place via the USB bus and can be carried out during final testing of the equipment.
• General-purpose I/Os: With the aid of the eight programmable inputs/outputs, the speaker manufacturer can differentiate his products from those of his competitors. For example, I2C bus interfaces and LCDs can be connected which display MP3 tracks.

These features give the speaker manufacturer scope for completely new options. He can use one and the same design for different speakers; only the content of the EEPROM has to be matched to the corresponding speaker type. Once created, designs can be used time and again. Furthermore, the manufacturer can pass on to the customer tonal characteristics measured in the laboratory, for example supplying classic, jazz or pop settings as presets. For the first time, independently of the sound card, the UAC 3552A therefore permits optimum matching of the PC and speaker systems.

A complete reference design on one circuit board is now available from MICRONAS. The package comprises the schematics, the complete software of a control unit and the software for the EEPROM control. Straightforward adjustment of the parametric 5-band equalizer is possible in Excel. In addition, MICRONAS offers macros in Visual Basic for Applications (VBA). Both can be easily integrated in the measuring instrument environment used by the speaker manufacturers.

MICRONAS supplies the UAC 3552A with pre-programmed on-chip EEPROM in a 44-pin quad flat package. The Windows-based programming software is part of the product range.