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EETE JULAUG 2012

account for up to 50 to 75 percent of the radio power consumption, with larger overheads. for ultra-low- power systems, the “one size fits all” standardized option is rarely the optimum solution. instead, design- ers developing solutions for ultra-low-power applica- tions should consider using the protocol best suited for their need. finally, link data rate is one of the most important factors influencing power consumption in duty-cycled wireless links. The average power is Fig. 2: Block diagram of a typical wireless sensor based on the ZL70250. almost inversely proportional to the link data rate; for instance, a 100kbps radio will consume almost half the power 2x3mm, it has standard 2-wire and sPi interfaces for control of a 50kbps radio for the same payload. when comparing Rf and data transfer using any standard microcontroller. The transceivers, “energy per bit” is a better indicator of power ef- microcontroller’s analog-to-digital converter (adC) connects to ficiency than current consumption. But high data rate radios are the ultra-low-power analog front-end device. Combined with often those with the higher peak currents, and these are highly the Zl70250 transceiver, the resulting solution can be used to undesirable for most small batteries as they result in large, develop a wireless eCG solution that can run continuously from leaky, storage capacitors. each of the aforementioned factors a CR series coin cell for up to a week. Similar power efficiency is critical for applications where power is at a premium and can be achieved with such devices as a 3-axis accelerometer or payload is greater than 10 bits/sec. Whereas previous body- pulse-oximeter for patient respiration measurement, as well as a worn wireless sensors could only be used for slowly varying variety of other wearable health monitoring platforms. parameters, new Rf technologies can be used to help observe The advent of micro-power batteries along with advances more rapidly changing physiological parameters, such as heart in ultra-low-power transceiver technology are making it pos- and brain electrical activity or blood oxygenation, that require sible to build smart, flexible and smart wireless sensors. Proper data rates on the order of 0.5 to 5 kbit/s to extract meaningful transceiver selection is critical for addressing a variety of key waveforms. one example of a solution that delivers this level design issues so that wearable wireless medical devices can of performance is the Zl70250 transceiver from Microsemi – perform continuous monitoring of bio-signals for long periods see figure 2. Housed in a chip-scale package measuring about using a single, low-cost battery. Get a New Picture of PCB-Prototyping and Production on Demand High speed laser structuring: LPKF ProtoLaser S Enjoy a clean process with all types of PCB materials. Minimal line/space width of 50/25 μm on ceramics. www.protolaser.com LPKF Laser & Electronics AG Phone +49 (0) 5131-7095-0 info@lpkf.com www.lpkf.com www.electronics-eetimes.com Electronic Engineering Times Europe July/August 2012 31


EETE JULAUG 2012
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