With increase of clock frequency, on-chip wire inductance starts to play an important role in power/ground distribution analysis, although it has not been considered so far. We perform a case study work that evaluates relation between decoupling capacitance position and noise suppression effect, and we reveal that placing decoupling capacitance close to current load is necessary for noise reduction. We experimentally show that impact of on-chip inductance becomes small when on-chip decoupling capacitance is well placed according to local power consumption. We also examine influences of grid pitch, wire area, and spacing between paired power and ground wires on power supply noise. When effect of on-chip inductance on power/ground noise is significant, minification of grid pitch is more efficient than increase in wire area, and small spacing reduces power noise as we expected.

This paper presents a thin, compact beacon transmitter operating without needing battery replacement by using a photovoltaic (PV) film harvester. The beacon is formed of a power-control circuit (PCC) that can monitor small amounts of power from the harvester and properly control mode switching at low-power consumption. This leads to the realization of a maintenance-free beacon requiring no battery replacement. The beacon prototype is 55×20×2 mm in size and has a PV cell of 3 cm2. It allows a start-up operation from just 44-lux illuminance. The PV area required for the operation can be 1.7 times smaller than that of conventional beacons, thanks to the current saving with appropriate sequential control of the PCC. Since the beacon makes operation possible in emergency stairs, underground passages and other dark places, the application field for Internet of things (IoT) services can be expanded. Furthermore, a beacon equipped with a secondary battery (BSB: Beacon with Secondary Battery) can be configured by adding a charge-discharge power monitoring circuit. The BSB transmits an advertising packet during the daytime while charging surplus power, and works using the stored power during the night; this results in a continuous operation for one week with one transmission every 3 seconds even at 0-lux illuminance. Without developing a new radiofrequency chip or module, commercial low-power devices can be easily adjusted depending on the application by adding appropriate power-control circuits. We are convinced that this design scheme will be effective as a rapid design proposal for IoT services.