Single-chip wireless solutions obviously require a single fabrication process, and for many members of the RF design community, CMOS is emerging as the technology of choice. This trend is reflected in Staccato's Ripcord , a Certified Wireless USB (CW-USB) solution implemented with a single CMOS IC.

While the fabrication process for the IC is relatively standard, the design process itself was a unique blend of engineering and business strategy focused on leveraging the advantages of manufacturing in CMOS. According to Roberto Aiello, CTO and co-founder of Staccato, one critical strategic business decision was to hire a design team with experience in designing Bluetooth and Wi-Fi systems entirely in CMOS.

Staccato was started in 2003 to capitalize on the potential of CW-USB. From the outset, the company was closely involved in defining the standard for CW-USB through the WiMedia Alliance to ensure CMOS friendliness. For example, the requirements for low transmit power and the choice of QPSK modulation to reduce amplifier linearity are choices that are compatible with CMOS capabilities. To address the concern for a bandwidth of 3 GHz, which was called for early in the specification for CW-USB, bandwidth partitions of 500 MHz were established.

Another important decision by Staccato was to wait until CW-USB had been fully defined before proceeding with the development of critical RF portions of the project . This was crucial for managing the complex interactions between subsystems on the chip, because an alteration in one subsystem made in response to a specification change could have required additional changes throughout the entire device. Once CW-USB was fully defined after the FCC regulatory process had been completed, the Ripcord IC was then designed and optimized for that finalized standard.

Aiello stated that CW-USB products from other vendors are based on chipsets rather than single chips mainly because the development of those projects began before the CW-USB specification had been fully defined. This required a design flexibility that could only be achieved using separate fabrication process technologies to optimize the baseband and RF functions.

The thoroughness of Staccato's business strategy was complemented with a careful engineering strategy. According to Aiello, Staccato selected and characterized the CMOS process first, and then proceeded to develop the Ripcord IC's circuit design and system architecture. The process selected was a 110-nm CMOS process from Fujitsu, a shrink of Fujitsu's 130-nm process. This shrink process supports RF functions and is also more efficient than the 130-nm process.

Once the basic design had been established, another important step was to immediately produce a test chip. This enabled design flaws in real silicon outside the scope of simulation tools to be detected and addressed quickly.

While the essence of the Ripcord is a single chip, the entire device is a system-in-package that includes all necessary passive components, including a crystal. In the future, there may be an option to remove this crystal and derive timing from a system clock on the host platform, such as a cell phone or laptop.

The antenna is external because small high-grade units are commercially available. There would also be system-level RF certification issues if the Ripcord module included an integrated antenna. In effect, the entire circuit board incorporating such a module would need to undergo the complete RF certification process.

The first application for the Ripcord is presently in USB dongle/hub pairs for wirelessly connected legacy USB devices. However, quickly following this retrofit market will be CW-USB embedded in PCs, hard drives, printers, digital cameras, and MP3 players. The emerging usage model will be for large file transfers, such as those for digital media content, transferred between two mobile devices or between a mobile device and a PC or its peripherals.

At present, the vast majority of Wi-Fi and Bluetooth implementations are single-chip CMOS solutions. These advances, taken together with the single-chip solution for the UWB technology used by CW-USB, indicate a new type of convergence.

Just as entertainment, navigation, and communications functions are converging in ever-shrinking handsets, RF, baseband, and non-volatile storage capabilities appear to be converging on ever-shrinking CMOS process technologies. With the advent of single-chip solutions, CW-USB will probably be a common factor in both of these continuing developments.

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