In wireless-sensor newtork systems, many wireless terminals collect information like temperature and humidity. ZigBee has been billed as the optimal solution for such networks. Yet Ultra Wideband Impulse Radio (UWB-IR) may prove to be an even better solution. Such thinking led to the development of a UWB-IR transmitter with a digitally controlled pulse generator by Hitachi Ltd.’s Takayasu Norimatsu, Ryosuke Fujiwara, Masaru Kokubo, and Masayuki Miyazaki in conjunction with Akira Maeki, Yuji Ogata, Shinsuke Kobayashi, Noboru Koshizuka, and Ken Sakamura from Tokyo’s YRP Ubiquitous Networking Laboratory.
Essentially, UWB-IR flaunts low power dissipation per data rate, which leads to longer battery life. In sensor networks, the transceiver transmits a certain size of data at regular intervals. Energy consumption decreases by shortening the transmission periods. For example, UWB-IR transceivers with sensors transmit 55 B of data per 5 min. in the sensor network system. When the data rate is 10 Mb/s, they operate for only 44 μs. In contrast, a ZigBee transceiver with a 250-kb/s data rate will operate for 3520 μs. The UWB-IR transceiver also enables ranging using pulse communication like radar. As a result, the network can detect the terminals’ locations automatically.
The UWB transmitter was fabricated by a 0.18-μm bulk CMOS process. With this digital-intensive architecture, the pulse shape can easily be adjusted. In addition, the chip area is just 0.40 mm2. The transceiver’s measured average power dissipation is 29.7 mW, thanks in large part to the intermittent operation of the power amplifier. See “A UWB-IR Transmitter with Digitally Controlled Pulse Generator,” IEEE Journal of Solid-State Circuits, June 2007, p. 1300.