An energy-harvesting system requires an energy-storing device to store the energy retrieved from the surrounding environment. Rechargeable batteries are commonly used to store this energy; however, because of the limited number of charge/discharge cycles, they need to be periodically replaced. A supercapacitor, which has, ideally, a limitless number of charge/discharge cycles, avoids this problem. In this case, it is required for the power management unit to produce a constant output voltage as the supercapacitor discharges. This paper presents a system with a multiratio switched capacitor DC-DC converter, in a 130-nm technology, with a maximum output power of 2 mW, a maximum efficiency of 79.63% and a maximum output ripple, in the steady state, of 23 mV for an input voltage range of 2.3-0.87 V. The proposed converter has four operation states, to maximize its efficiency, that correspond to the conversion ratios of 1/2, 2/3, 1/1 and 3/2. Its clock frequency is automatically adjusted to produce a stable output voltage of 1 V. These features are implemented through two distinct controller circuits that use two asynchronous time machines to dynamically adjust the clock frequency and to select the active state of the converter. All the theoretical expressions as well as the behaviour of the whole system were verified by using electrical simulations.When the transmission gate is on, the driver produces a complementary clock signal of ϕ 2 from V in to zero. When the transmission gate is off and M 3 is on, the inverter produces V in that turns off the switch. Figure 11. Transistors in the bold line are 3.3-V transistors, and those in the normal lines refer to 1.2-V transistors. PMOS and NMOS with undefined bulk have their bulk connected to V in /V out and ground respectively. 2028 R. MADEIRA AND N. PAULINO
An energy harvesting system can use a supercapacitor in order to store energy; however, a voltage regulator is required to obtain a constant output voltage as the supercapacitor discharges. A Switched-Capacitor DC-DC converter allows for complete integration in CMOS technology, but requires several topologies in order to obtain a high efficiency. This paper presents the complete analysis of these topologies in order to determine expressions that allow to design and determine the optimum input voltage ranges for each topology. These expressions are verified using electrical simulations.
A very low-cost portable Multichannel Analyzer (MCA) built with off-the-shelf commercial components is presented. Built around an universal microcontroller based platform for portable instruments, previously developed in our group, this intelligent portable MCA is operated by multicell Li-ion batteries and has power, and memory autonomy, for several hours of spectra collecting. The MCA integrates a basic frontend pulse shape amplifier, a base line restorer, a peak detector and logic control circuitry. The growing of the radiation spectrum can be easily observed on site through a dot-matrix graphic display. To save the acquired data and allow for the configuration of setup parameters, it connects to any host computer through standard USB, IrDA or RS-232 serial interfaces being also prepared to interface a GPS unit. Software application programs in both the portable MCA and the host PC are presented.
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