CMOS RF transceivers for wireless sensor networks

Jae Hyuk Jang, Purdue University

Abstract

CMOS RF transceivers for wireless sensor networks for two discriminative sensor network applications are presented; one is an energy-constraint WSN, requiring low-power and self-contained operation powered by a piezoelectric energy harvester. The other is a high-throughput WSN, requiring a real-time, high-precision, and high-data- rate operation with improved multi-node capacity using collaborative OFDMA. The target application of the energy-constraint WSN is a condition monitoring on mechanical structures. The WSN is self contained with the power generated by the piezoelectric energy harvester producing about 100 μW. The corresponding sensor network utilizes an asynchronous beacon-detection based duty cycle control architecture to reduce power consumption and support ID-based TDMA while avoiding the need for timing synchronization between nodes. It also provides FDMA and fixed time slot TDMA for further network flexibility. The sensor node transceiver includes a duty-cycle timing control unit to minimize power consumption; an LO-less, TDMA-capable, addressable beacon receiver; an FDMA-capable transmitter; and a low power, universal sensor interface. The proposed sensor node, implemented in 0.13-μm CMOS technology, achieves low power consumption and a high degree of flexibility without calibration or the use of BAW or SAW filters. The sensor node is experimentally demonstrated to operate autonomously from the power provided by a piezoelectric vibration energy harvester with dimensions of 27 × 23 × 6.5 mm3 excited by 4.5-m/s2 acceleration at 40.8 Hz. The WSN condition monitoring behavior is measured with a capacitive temperature sensor, and achieves an effective temperature resolution of 0.36°C. The high-throughput WSN is utilized for a real-time spatial pressure sensing application with the improved spectrum efficiency using collaborative OFDMA. The WSN achieves a small size by replacing bulky batteries and crystals with wireless powering and clocking techniques. The wireless clocking also enables the symbol synchronization between different nodes required for collaborative OFDMA which improves spectrum efficiency by twice over FDMA. The sensor nodes are fabricated in 0.13-μm CMOS technology, and each node consumes 43.8 mW. The nodes uses a piezoelectric pressure sensor to detect the pressure data. The ADC's resolution is 8 bit, and the temporal resolution is 2 Msps, implementing 16-Mbps data rate per node, with 4 Msps symbol rate for 16-QAM symbols. An integer-N PLL is used to achieve channel spacing with 4MHz frequency step between adjacent channels. Five sensor nodes in adjacent channels are tested to verify the collaborative OFDMA operation. The center channel at 3.468 GHz showed 14.3% EVM, degraded by 7.8% compared to the single node case in which no channel overlapping occurred. In addition, the actual wireless pressure monitoring behavior of the sensor node is measured showing the reasonable similarity with the traditional wired pressure monitoring test result.

Degree

Ph.D.

Advisors

Jung, Purdue University.

Subject Area

Electrical engineering

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