Wednesday, March 28, 2007

Bigger is cheaper for Zigbee

Fabless chip designer Jennic in Sheffield has developed a reference design for Zigbee low power embedded wireless nodes that costs well under $5.
This includes the cost of the Jennic JN5139 wireless microcontroller, a high performance PCB antenna design, and all other ancillary components, and now allows the use of wireless connections for devices such as thermostats and light switches to on installation costs when compared to wired solutions.
The sub $5 price point is achieved by making things larger. Jennic has eliminated the antenna and RF balun (the other key component in the RF path) components by using a larger, balanced antenna printed on the circuit board, requiring no additional components to match the chip's 200 ohm resistive differential RF interface. This gives a 1.5dB improvement in receive sensitivity and transmit power along with higher gain (around 4dBi) than a ceramic antenna (approximately 1.5dBi) and gives the node a range of up to 1km (or helps keep the power down for shorter distances).
Similarly for the crystal, Jennic has used a HC49U surface mounted package measuring approximately 12.5x3.7x4.2mm high, which costs about half the price of equivalent miniature devices. The increased physical size of the resonating element gives higher performance - the equivalent series resistance is smaller, resulting in lower system phase noise and faster oscillator start-up times, saving on overall system power consumption.
But even with these, the two-layer board still measures only 49x25mm to keep the cost of the board to a minimum. The ZigBee/IEEE802.15.4 design is freely available from Jennic's support website - www.jennic.com/support.

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