RF chip set provides CD-quality digital audio wireless links
( 01 May 2003 )
Terry Koh in Singapore
The market for digital RF transmission is driven largely by data applications. High-end audio applications often have to battle with data-centric idiosyncrasies such as data fragmentation, high latency and lack of determinism.
FreeSystems, a Singapore-based digital audio semiconductor company, has introduced what it claims is the first audio-centric digital RF chip set on the market. The FreeSpan FS2103 chip set promises CD-quality digital audio wireless links using RF. It targets consumer products such as wireless headphones, extension speakers, wireless surround speakers, and high-performance wireless digital audio links. The FS2103 supports transmission over both the 900 MHz and 2.4 GHz ISM bands.
The companion pair comprises the FS2103TX transmitter chip and the FS2103RX receiver chip, and their high integration minimizes system costs and reduces design time.
The chips provide a robust, low-latency (12 ms, suitable for Dolby applications) digital link with proprietary error-correction and jitter reduction algorithms, and dual antenna diversity system support. Full-bandwidth stereo audio is transmitted in uncompressed digital format, resulting in a signal-to-noise ratio of up to 96 dB. Transmission occurs over one of four frequency channels, and the receiver has an auto-scanning function so the user need not select the appropriate channel manually.
In these FreeSpan designs, the algorithms and other key functions are implemented in a hard-wired processor, resulting in higher performance at lower power consumption. The transmitter chip consumes 25 mA at 3.3V and the receiver 38 mA at 3.3V.
The audio interface to the chips is a 48 ksamples/s I2S interface. A serial EEPROM interface also allows the chips to store customization and configuration data.
A simple “soft key” interface transmits error-checked control data: the states of four input pins on the transmitter chip are sampled and sent as four data bits every 5 ms. Furthermore, a reverse channel (from receiver chip to transmitter chip) is available, providing two data bits every 5 ms. (Implementing this reverse channel in a product would require the RF front-end sections to be transceivers.) With a µP or other logic, more sophisticated use of these control bits would obviously be possible.
The fully-functional board-level modules containing the FS2103TX or FS2103RX are priced at US$20 per module in production quantities. Evaluation kits are also available at US$1,000 each. Both chips are packaged in fine-pitch, 80-pin, 12-mm square TQFP packages. Mounting height is 1.5 mm.
