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Transceiver reduces power for wireless connectivity

Posted: 14 Nov 2005 ?? ?Print Version ?Bookmark and Share

Keywords:cypress semiconductor? wirelessusb? cyrf6936? transceiver?

Designers of wireless mouse/keyboard combinations, remote controls and wireless/VoIP headsets are highly concerned with power consumption. As with all portable equipment, consumers want exceptional functionality, long battery life, and low cost. Looking to lock in a lead in this market, Cypress Semiconductor designed its second-generation WirelessUSB product which is also known as WirelessUSB LP or part number CYRF6936.

In terms of functionality, one of the key issues with such a product is: will it work? While this may sound a bit flippant, Dave Wright, WirelessUSB LP Chip architect explained, "Not only does the wireless product need to operate in the presence of potentially interfering systems, such as WiFi, cordless phones, Bluetooth and microwave ovens, it also needs to be able to be located near other similar products." For instance, 27MHz is the currently more popular frequency for wireless keyboards/mouse combinations. "Unfortunately, 27MHz is unworkable in a typical close office environment with more than two systems," said Wright, "In some 27MHz systems, an employee is typing on one computer, and the work has been known to appear on someone else's computer. This is, by far, the greatest limitation of 27MHz technology."

Cypress is using 2.4GHz direct sequence spread spectrum (DSSS) technology for its devices, and credits DSSS with allowing it to achieve excellent performance in complex wireless environments. Wright notes that in this market, datasheets cannot prove that a product works in an environment that has many potential interferers. "We provide our customers with reference designs and set up tests that push our products to the limit, setting up the worst imaginable environments with multiple WiFi, cordless phones, Bluetooth devices, and collocated systems to test our device and protocol together and demonstrate link robustness," says Wright.

The device demonstrates a data rate of 1Mbps in GFSK mode 250 kb/s in DSSS mode. The team reports that the number one design challenge for this chip was trading off features/performance/time-to-market/die size. The early technical challenge facing the team was how to improve the DSSS data rate without trading off robustness. "We developed innovative, patent pending techniques in order to drive up the data rate without sacrificing throughput."

Well, that addresses performance, but what about power consumption? "With this product, we have reduced the power consumption significantly, resulting in 1 year of battery life on a wireless mouse with typical usage," reported Aravind Nagarajan, Product Manager for the WirelessUSB LP.

The design team reports that it redesigned the entire chip from the ground up to be completely focused on low power. "We changed the system architecture somewhat to minimize the block by block current at a circuit design level, and, from an architecture point of view we developed as low as possible power blocks," explained Wright. The team also addressed voltage, which is a concern for devices in this market space. The new chip design integrates a boost converter (with 85% efficiency) for the blocks on the device that need to operate above 1.8V, and it can also supply external devices that require boosted voltage, such as the microcontroller in a keyboard. This feature allows for the use of lower-cost microcontrollers and reduces the overall BOM.

Other nice features that make this device worthy of a closer look include an autotransaction sequencer that automatically switches from Tx to Rx mode without microcontroller intervention, an autorate transceiver, and the company's KISSBind and TouchWake technologies to simplify installation and minimize battery consumption, respectively. Besides these integrated features that improve performance, Cypress also provides its customers with the source code for its WirelessUSB protocol, which they can use in total or customize; this saves R&D time in protocol development and speeds time to revenue.

The CYRF6936 is priced at $1.20 each in high volumes. It is sampling now with full production quantities expected in Q1 2006.

- Janine Love


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