The emergence of personal-area networking” is giving rise to a new crop of wireless-technology developers that could shake up the ranks of the established players.

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The emergence of personal-area networking” is giving rise to a new crop of wireless-technology developers that could shake up the ranks of the established players.

RNC50H9761BSRSL31_Vishay Dale_Through Hole Resistors

The emergence of personal-area networking” is giving rise to a new crop of wireless-technology developers that could shake up the ranks of the established players.

The Commetrex's M.100 algorithms range from $29 for basic telephony to $150 for high-speed data modems. A typical configuration of hardware and software for eight lines of voice and fax would list at $318 per port, with volume discounts available that take the price per port down to $190.

CALL (770) 449-7775www.commetrex.comEETInfo No. 649

RNC50H9761BSRSL31_Vishay Dale_Through Hole Resistors

BERKELEY, Calif. — Researchers at the University of California at Berkeley's Materials Sciences Division have discovered a way to create junctions between carbon nanotubes, a development that presages the fabrication of molecular electronic nanotube circuits.

Studies of carbon nanotubes have shown that the tiny, wirelike structures can produce insulating, conducting and semiconducting behavior, depending on the configuration of carbon atoms in their walls.

The basic experiment crossed a conducting nanotube with a semiconducting nanotube to create a Schottky barrier. In silicon systems, Schottky barriers are a simple type of heterojunction formed by a high-quality interface between a metal and the substrate.

RNC50H9761BSRSL31_Vishay Dale_Through Hole Resistors

The junction was formed by placing the two carbon nanotubes in an X on a substrate. Each tube had electrical connections at each end, and the substrate was also electrically biased to adjust the charge per unit length on the wires. The conducting tubes were relatively unaffected by the bias voltage, but the semiconducting wires were found to be conducting at negative voltages and insulating at positive voltages, characterizing them as p-type semiconductors. Studies of various configurations showed that the best tunneling contacts occurred between two conducting nanotubes.

The actual area for current flow is very small, about a square nanometer. Given the pace of research and development in nanotube manufacturing capability today, combined with experience in using atomic-force microscopes to manipulate the wires, the nanotube junctions could become a quick route to molecular electronics.

RNC50H9761BSRSL31_Vishay Dale_Through Hole Resistors

SAN MATEO, Calif. — Philsar Semiconductor Inc. announced a two-way RF device that integrates both the transmit and receive functions onto a single chip. The company is being acquired by Conexant Systems Inc. and expects the new technology to become an important part of Conexant's suite of products.

This is aimed at products that currently use only one-way RF functions,” said Jeff Robillard, product marketing manager for the Ottawa, Canada-based company. Keyless entry devices for cars, remote control units for home entertainment systems, wireless sensors and PDAs are applications that can benefit from a two-way device. Using one-way technology limits the features that can be implemented, but adding two-way capabilities increases the features an OEM can offer,” said Robillard.

For a low-power design (100 mA), the connection provides an elegant solution to many switchover problems. A more typical solution for this might use steering diodes to select the higher of the two input sources. This approach is fine when the input voltages are high and the diode forward voltage drop is small compared with the battery voltage. But when the battery is a two-cell alkaline stack, a 0.3-V Schottky voltage drop wastes more than 10 percent of the available energy-a stiff penalty. The loss can be reduced by replacing steering diodes with power MOSFETs-this is frequently done with success, but not without added cost and complexity.

A battery-to-ac wall adapter to back up battery switchover circuitry is a common source of circuit bugs that are too often uncovered late in a design. Problems that can arise include: excess power loss in steering diodes, unforeseen reverse current through FET switch body diodes, Vcc dropout, and system reset during handoff from one power source to the next.

In another type of buck-boost solution, the connection works well when boosting from a low-voltage battery power (two AAs), or stepping down from a somewhat regulated wall adapter: It counts on the wall-powered supply to always be greater than the battery, but not more than 6.5 V to stay within the power and voltage limits of the SOT23 regulator IC. Since heat sinks are usually not appropriate for portable designs, an all-switch-mode approach would be more appropriate for higher power levels, or if the wall source is unregulated.

In a complete power supply design for a medium-power portable device such as a full-featured organizer or handheld inventory or point-of-sale (POS) computer, the peak output is about 2 W. Portable operation is from two AA batteries (typically NiCd) which are boosted to 3.3 V at up to 600 mA (during load peaks). Since the input from the ac or car adapter covers too wide a range, linear regulation is not an option. This also allows dc input voltages to be as low as 4 V. Most power steering diodes or FETs are eliminated by combining power sources at the output of the regulators rather than at the input. This is made possible by ICs that have milliamp-level shutdown modes as well as very low operating currents.

The supply also uses a lithium coin cell to back up RAM when no other power source is available. Since the cell voltage may be as low as 2.7 V, a small (micro-8) charge-pump boost converter generates a regulated 3.3 V when commanded by the BATT NG (battery no good) line. An IC generates the high-voltage supply required by the LCD panel. Its operation is also gated by OK” signals from the dc supply or the battery.


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