CSR fields new Bluetooth chips for handsets, headsets

Not to be outdone, CSR has launched its sixth generation of BlueCore silicon for Bluetooth. The BC6-ROM chip is designed for use in handset applications, while the BC6-Audio-ROM is designed for use in headset applications.

As the heir-apparent to the company's BlueCore3, BlueCore6 (BC6) has been specifically designed to offer better voice quality, lower power consumption, better RF performance, a smaller BOM, smaller footprint and easy host interfacing.

So, how did CSR achieve all this?

For voice quality, CSR departed from relying solely on the traditional continuous variable slope delta (CVSD) modulation scheme required by the Bluetooth Specification. In this generation, CSR has introduced AuriStream, a baseband codec option that has the potential to improve either voice quality or power consumption by up to 40 percent. Here's how it works. AuriStream uses adaptive differential pulse code modulation (ADPCM), a low-duty cycle modulation alternative that performs the same functions of CVSD at half the rate (ADPCM scans at 32Kbps while CVSD scans at 64Kbps).

"The addition of ADPCM has allowed us to boost our audio score from 2.46 with CVSD to 4.14, which is analogous to fixed-line voice quality," explained Gene Yan, regional manager for CSR.

Better performance
To address power consumption, the design team at CSR implemented a conditional scan and casual scan feature in the BC6-ROM. What this means is that unlike a traditional full-page conditional scan, the BC6-ROM immediately looks for RF activity in the 2.4GHz band. If it does not detect any, it powers down right away. If it does detect activity, then it initiates a full scan. With the casual scan feature, the BC6-ROM only powers up when the baseband chip is active. With this approach, the Bluetooth silicon does not unnecessarily wake up the host VCTXO (usually shared with the handset). By restructuring how the device scans for other devices, the company reports an 86 percent improvement in Bluetooth power consumption in scan mode. The BC6-Audio-ROM (the headset version) includes the conditional scan feature.

But what about RF performance? The BC6-ROM device incorporates an improved radio. The QFN version provides an impressive 10dBm Tx power and receive sensitivity of -90dBm. As a result, the device offers Class 1 performance (100m/300ft range) without an external power amplifier. Even though this range is often not required in Bluetooth applications, this level of RF performance enables better voice quality in environments with interference. This even includes the so called "cross body interference" caused by the users body when the mobile phone is worn on the belt and interacts with a headset.

The new devices have also been engineered to coexist with Wi-Fi and a Wi-Fi/Bluetooth reference design is available. In terms of size, the BC6-ROM requires 11.2mm? of PCB space and requires only nine passive devices, a balun, and antenna.

The new BC6 devices are also the first generation from CSR to include SDIO and SCPI interfaces, in addition to the UART interface offered in the past. These new interfaces position the devices to support upcoming broader bandwidth and multimedia applications.

The BC6 devices will begin sampling in November/December, with production scheduled for January/February 2008.

- Janine Love
RF Designline