The potential for collaborative, robust networks of microsensors has attracted a great deal of research attention. For the most part, this is due to the compelling applications that will be enabled once wireless microsensor networks are in place; location-sensing, environmental sensing, medical monitoring and similar applications are all gaining interest. However, wireless microsensor networks pose numerous design challenges. For applications requiring longterm, robust sensing, such as military reconnaissance, one important challenge is to design sensor networks that have long system lifetimes. This challenge is especially difficult due to the energyconstrained nature of the devices. In order to design networks that have extremely long lifetimes, we propose a physical layer driven approach to designing protocols and algorithms. We first present a hardware model for our wireless sensor node and then introduce the design of physical layer aware protocols, algorithms, and applications that minimize energy consumption of the system. Our approach prescribes methods that can be used at all levels of the hierarchy to take advantage of the underlying hardware. We also show how to reduce energy consumption of non-ideal hardware through physical layer aware algorithms and protocols.

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Energy conscious software design can significantly improve the energy efficiency of a portable system. A software energy estimation technique using instruction class profiling is presented. The technique is shown to have an estimation error of less than 3% with trivial runtime overhead, based on a set of application programs evaluated on the StrongARM SA-1100 and Hitachi SH-4 microprocessors. A technique to isolate the switching and leakage energy components of software is outlined. The energy overhead of a real-time operating system is also profiled. The overall impact of system-level software energy management is quantified using the MIT AMPS system as an application example.Index Terms-Instruction current profiling, low power, software energy, system-level energy management.

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We report a novel room temperature methanol sensor comprised of gold nanoparticles covalently attached to the surface of conducting copolymer films. The copolymer films are synthesized by oxidative chemical vapor deposition (oCVD), allowing substrate-independent deposition, good polymer conductivity and stability. Two different oCVD copolymers are examined: poly(3,4-ethylenedioxythiophene-co-thiophene-3-aceticacid)[poly(EDOT-co-TAA)] and poly(3,4-ehylenedioxythiophene-co-thiophene-3-ethanol)[poly(EDOT-co-3-TE)]. Covalent attachment of gold nanoparticles to the functional groups of the oCVD films results in a hybrid system with efficient sensing response to methanol. The response of the poly(EDOT-co-TAA)/Au devices is found to be superior to that of the other copolymer, confirming the importance of the linker molecules (4-aminothiophenol) in the sensing behavior. Selectivity of the sensor to methanol over n-pentane, acetone, and toluene is demonstrated. Direct fabrication on a printed circuit board (PCB) is achieved, resulting in an improved electrical contact of the organic resistor to the metal circuitry and thus enhanced sensing properties. The simplicity and low fabrication cost of the resistive element, mild working temperature, together with its compatibility with PCB substrates pave the way for its straightforward integration into electronic devices, such as wireless sensor networks.

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Extreme energy constraints inherent in many exciting new wireless sensing applications (such as [1][2][3]) virtually dictate that such systems operate with extremely low duty cycles, harvesting and storing energy over long periods of time before waking up to perform brief measurement and communication tasks. However, such duty cycling only works if the sleep power of the system is less than the average power available from the power source, which may only be as much as a few nA. In this work, we present an RF transmitter designed to operate in an extremely low duty-cycle industrial monitoring system. The primary challenges are achieving high efficiency in the active mode while transmitting as high as +10dBm and simultaneously minimizing the leakage during the sleep mode. We address these in a +10dBm Bluetooth Low Energy (BLE) transmitter test-chip through 1) low voltage design (0.68V) for switching power and short-circuit power reduction, 2) extensive power gating of unused blocks and 3) a negative-VGS biasing technique for PA leakage reduction without affecting its on-performance.Typically, high-VT power switches are used to power gate low-VT active circuits [1]. But, the switch resistance, which is in the direct path of active current, degrades on-performance. Increasing switch size will in turn increase leakage. Negative gate-biasing of the gating switch has been shown to give significant leakage reduction [3]. However, in this work, we study the effect of negative-gate biasing of the low-VT active device itself, thereby eliminating a switch in the direct path of active current and simultaneously reducing leakage. This is especially useful for the PA in our work, which operates at +10dBm and is the largest active power consumer. Fig. 13.7.1 shows the measured drain current (ID,PA) and gate current (IG,PA) of the NMOS PA transistor as a function of the negative gate bias applied. The 65nm CMOS transistor, because of its thin gate oxide, has significant gate leakage. It is exponential with the gate bias. The drain current, which is the sum of sub-threshold current and gate leakage, decreases exponentially with increasing gate bias while the sub-threshold current is dominant, but increases as gate leakage becomes larger. The red curve (in solid) shows the achievable total PA leakage assuming the negative bias is supplied by an ideal −½ charge pump (ILEAK = ID,PA-½IG,PA). The minimum, 430pA, occurs at −200mV and represents a 30× reduction in leakage. Fig. 13.7.1 also shows a histogram of the minimum (ID,PA−½IG,PA) current for 25 measured chips. Simulations indicate that the minimum leakage points range from −150mV to −300mV, which implies that a −½ charge pump generating VNEG =−½VIN is sufficient. Low VDD ensures device reliability even with VNEG biasing (VDD-VNEG < 1.2V). Fig. 13.7.2 shows the complete TX system block diagram. The RF signal path has a 12MHz crystal oscillator feeding a divided 1MHz clock to an integer-N PLL. The PLL provides 2MHz-spaced BLE channels at 2.4GHz. The PLL output is then buffered ont...