The electronics of a general biomedical device consist of energy delivery, analog-to-digital conversion, signal processing, and communication subsystems. Each of these blocks must be designed for minimum energy consumption. Specific design techniques, such as aggressive voltage scaling, dynamic power-performance management, and energy-efficient signaling, must be employed to adhere to the stringent energy constraint. The constraint itself is set by the energy source, so energy harvesting holds tremendous promise toward enabling sophisticated systems without straining user lifestyle. Further, once harvested, efficient delivery of the low-energy levels, as well as robust operation in the aggressive low-power modes, requires careful understanding and treatment of the specific design limitations that dominate this realm. We outline the performance and power constraints of biomedical devices, and present circuit techniques to achieve complete systems operating down to power levels of microwatts. In all cases, approaches that leverage advanced technology trends are emphasized.

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Wireless microsensor networks, which have been the topic of intensive research in recent years, are now emerging in industrial applications. An important milestone in this transition has been the release of the IEEE 802.15.4 standard that specifies interoperable wireless physical and medium access control layers targeted to sensor node radios. In this paper, we evaluate the potential of an 802.15.4 radio for use in an ultra low power sensor node operating in a dense network. Starting from measurements carried out on the off-theshelf radio, effective radio activation and link adaptation policies are derived. It is shown that, in a typical sensor network scenario, the average power per node can be reduced down to 211µ µ µ µW. Next, the energy consumption breakdown between the different phases of a packet transmission is presented, indicating which part of the transceiver architecture can most effectively be optimized in order to further reduce the radio power, enabling self-powered wireless microsensor networks.

A 1 Mbps 916.5 MHz OOK transceiver for wireless sensor networks has been designed in a 0.18-µm CMOS process. The RX has an envelope detection based architecture with a highly scalable RF front end. The RX power consumption scales from 0.5 mW to 2.6 mW, with an associated sensitivity of-37 dBm to-65 dBm at a BER of 10 −3. The TX consumes 3.8 mW to 9.1 mW with output power from-11.4 dBm to-2.2 dBm. The RX achieves a startup time of 2.5 µs, allowing for efficient duty cycling.

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This paper presents an all-digital, non-coherent, pulsed-UWB transmitter. By exploiting relaxed center frequency tolerances in non-coherent wideband communication, the transmitter synthesizes UWB pulses from an energy-efficient, single-ended digital ring oscillator. Dual capacitively coupled digital power amplifiers (PAs) are used in tandem to attenuate low frequency content typically associated with single-ended digital circuits driving single-ended antennas. Furthermore, four level digital pulse shaping is employed to attenuate RF sidelobes, resulting in FCC compliant operation in the 3.5, 4.0, and 4.5 GHz IEEE 802.15.4a bands without the use of any off-chip filters or large passive components. The transmitter is fabricated in a 90 nm CMOS process and occupies a core area of 0.07 mm 2. The entirely digital architecture consumes zero static bias current, resulting in an energy efficiency of 17.5 pJ/pulse at data rates up to 15.6 Mb/s.

Abstract-A 1 Mbps 916.5 MHz OOK transceiver for wireless sensor networks has been designed in a 0.18-µm CMOS process. The RX has an envelope detection based architecture with a highly scalable RF front end. The RX power consumption scales from 0.5 mW to 2.6 mW, with an associated sensitivity of -37 dBm to -65 dBm at a BER of 10 −3 . The TX consumes 3.8 mW to 9.1 mW with output power from -11.4 dBm to -2.2 dBm. The RX achieves a startup time of 2.5 µs, allowing for efficient duty cycling.Index Terms-energy efficient, low power, sensor networks, transceivers.

Emerging microsystems such as portable and implantable medical electronics, wireless microsensors and next-generation portable multimedia devices demand a dramatic reduction in energy consumption. The ultimate goal is to power these devices using energy harvesting techniques such as vibration-to-electric conversion or through wireless power transmission. A major opportunity to reduce the energy consumption of digital circuits is to scale supply voltages to 0.5V and below. The challenges associated with ultra-low-voltage design will be presented. These include variation-aware design for logic and SRAM circuits, efficient DC-DC converters for ultra-low-voltage delivery, and algorithm structuring to support extreme parallelism. This paper also addresses micro-power analog and RF circuits, which require the use of applicationspecific structures and highly digital variation-aware architectures.