Hiroki Asano

Ultra-wideband surface acoustic wave devices using Cu-Grating/Rotated-YX-LiNbO3-Substrate structure

This paper discusses the application of Love mode propagating on Cu-grating/rotated YX-LiNbO3-substrate structure to the development of ultra-wideband and low-loss RF surface acoustic wave (SAW) filters. Theoretical analysis suggested that high performance resonators with very small capacitance ratio would be realised using Cu gratings with a thickness of several percent of wavelength. It was also suggested that in particular, on 15°YX-LiNbO3-substrate structure, the spurious response due to Rayleigh mode could effectively be suppressed. An IDT-type one-port SAW resonator and a ladder-type SAW filter were fabricated on the Cu-grating/15°YX-LiNbO3-substrate structure, and their high performances are demonstrated with discussion.

Wideband Love wave filters operating in GHz range on Cu-grating/rotated-YX-LiNbO/sub 3/-substrate structure

The paper discusses the application of Love mode propagating on Cu-grating/rotated YX-LiNbO/sub 3/-substrate structure to the development of ultra-wideband and low-loss RF SAW filters. Theoretical analysis suggests that high performance resonators with very small capacitance ratio may be realised using Cu gratings of the thickness of several percent of wavelength. It was also suggested that, in particular, on a 15/spl deg/YX-LiNbO/sub 3/-substrate structure, the spurious response due to the Rayleigh mode could effectively be suppressed. IDT-type one-port SAW resonators and ladder-type SAW filters were fabricated on the Cu-grating/15/spl deg/YX-LiNbO/sub 3/-substrate structure, and their high performances are demonstrated by discussion.

Fully-Integrated High-Conversion-Ratio Dual-Output Voltage Boost Converter With MPPT for Low-Voltage Energy Harvesting

This paper proposes a fully-integrated high-conversion-ratio dual-output voltage boost converter (VBC) with maximum power point tracking (MPPT) circuits for low-voltage energy harvesting. The VBC consists of two voltage generators that generate V_OUT1 and V_OUT2. V_OUT1 and V_OUT2 are three and nine times higher than the harvesters output V_IN, respectively. V_OUT1 is used as a supply voltage for on-chip application circuits while V_OUT2 is used as the charging voltage for a Li-ion secondary battery. The VBC achieves a high voltage conversion ratio (max. × 9) and a high power conversion efficiency. The MPPT circuits control the operating frequencies of the CPs to extract maximum power at each output. The measurement results demonstrated that the circuit converted a 0.59 V input to a 1.41 V output with 75.8% efficiency when the output powers of V_OUT1 and V_OUT2 were 396 and 0 μW, respectively, and a 0.62 V input to a 4.54 V output with 49.1% efficiency when the output powers were 0 and 114 μW, respectively.

A fully-integrated, high-conversion-ratio and dual-output voltage boost converter with MPPT for low-voltage energy harvesting

This paper proposes a fully-integrated high-conversion-ratio dual-output voltage boost converter (VBC) with maximum power point tracking (MPPT) circuits for low-voltage energy harvesting. The VBC consists of two voltage generators that generate VOUT1 and VOUT2. VOUT1 and VOUT2 are three and nine times higher than the harvesters output Vin, respectively. VOUT1 is used as a supply voltage for on-chip application circuits while VOUT2 is used as the charging voltage for a Li-ion battery. The VBC achieves a high voltage conversion ratio (max. × 9) and a high power conversion efficiency with a small number of charge pumps (CPs). The MPPT circuits control the operating frequencies of the CPs to extract maximum power at each output. The measurement results demonstrated that the circuit converted a 0.59-V input to a 1.41-V output with 75.8% efficiency when the output powers of VOUT1 and VOUT2 were 396 and 0 μW, respectively, and a 0.62-V input to a 4.54-V output with 49.1% efficiency when the output powers were 0 and 114 μW, respectively.

SAW reflection characteristics of Cu electrodes and their application to SAW IF devices

This paper describes the application of copper (Cu) electrodes to SAW devices employing metal grating reflectors. It is shown both theoretically and experimentally that the metal grating made of Cu electrodes on 128/spl deg/YX LiNbO/sub 3/ gives much larger reflectivity than that made of Al electrodes of the same thicknesses. As one of the applications of Cu electrodes to SAW IF devices, the directivity of Cu-SPUDT is shown experimentally to be 10 dB larger than that of Al-SPUDT. It is also discussed that optimally weighted grating reflectors can be designed by employing Cu electrodes. The result concludes that Cu electrodes on 128/spl deg/YX - LiNbO/sub 3/ could further enhance the performance of SAW IF devices employing metal grating reflectors.

Ultra wideband Love wave devices employing Cu-grating/rotated YX LiNbO/sub 3/-substrate structure

This paper discusses the application of Love mode propagating on Cu-grating/rotated YX-LiNbO/sub 3/-substrate structure to the development of ultra-wideband and low-loss RF SAW filters. Theoretical analysis suggested that high performance resonators with very small capacitance ratio would be realised using Cu gratings of the thickness of several percent of wavelength. It was also suggested that in particular, on 15/spl deg/YX-LiNbO/sub 3/-substrate structure, the spurious response due to Rayleigh mode could effectively be suppressed. An IDT-type one-port SAW resonator and ladder-type SAW filter were fabricated on the Cu-grating/15/spl deg/YX-LiNbO/sub 3/-substrate structure, and their high performances are demonstrated with discussion.

Single-Phase Unidirectional Surface Acoustic Wave Transducer Using Cu Electrode

This paper proposes the application of Cu electrodes to surface acoustic wave single-phase unidirectional transducers (SAW SPUDTs). Since SPUDTs require large and widely variable reflectivity obtained by relatively thin electrodes, Cu with large mass density is one of the candidate materials. First, SAW reflection characteristics of a Cu electrode on 128°YX-LiNbO3 were theoretically investigated. It is shown that Cu electrodes offer much larger reflectivity than Al electrodes. In addition, SAW velocity change with electrode width is quite moderate compared with other materials having large mass density such as Au. An SPUDT was fabricated employing Cu electrodes to discuss how effectively SAW reflectivity contributes, for example, to its unidirectionality. As a result, the obtained directivity for the Cu-SPUDT was about 16 dB, which was 10 dB larger than that for an SPUDT employing conventional Al electrodes.

A fully on-chip three-terminal switched-capacitor DC–DC converter for low-voltage CMOS LSIs

In this paper, we present a fully on-chip switched-capacitor DC–DC converter for low-voltage CMOS LSIs. The converter has three terminals of input, ground, and output, by developing control circuits with fully on-chip configuration. We employ an ultra low-power nanoampere bias current and voltage reference circuit to achieve ultra low-power dissipation of control circuits. It enables us to realize a highly efficient power conversion circuit at light-load-current applications. The converter achieves highly efficient and robust voltage conversion using a pulse frequency modulation control circuit and a start-up/fail-safe circuit. Measurement results demonstrated that the converter can convert a 3.0 V input into 1.2 V output successfully. The start-up and fail-safe operations were confirmed through the measurement. The efficiency was more than 50% in the range of 2–6 µA load current.

An area-efficient, 0.022-mm2, fully integrated resistor-less relaxation oscillator for ultra-low power real-time clock applications

In this paper, we propose a fully integrated and area-efficient resistor-less relaxation oscillator (ROSC) for ultra-low power real-time clock (RTC) applications. The proposed ROSC is based on a conventional ROSC and modified to be area-efficient circuit configuration, without using resistors. The proposed ROSC consists of a bias current source, proportional to absolute temperature (PTAT) voltage source, current mode ROSC, shunt regulator, and output logic circuit. The PTAT voltage source and shut regulator are used to compensate for the temperature characteristics of the ROSC. By implementing our proposed ROSC in a 65-nm CMOS process, the area was 0.022 mm2. Simulated results demonstrated that our proposed ROSC generates 32.5-kHz clock frequency and achieves ultra-low power dissipation of 271 nW. The temperature and voltage dependences of the oscillation frequency were 138ppm/°C and 13.9ppm/mV, respectively. Monte Carlo statistical simulations showed that the mean, standard deviation, and the coefficient of variation are 32.3 kHz, 0.6 kHz, and 1.9%, respectively.

Sub-1-μs start-up time, 32-MHz relaxation oscillator for low-power intermittent VLSI systems

We propose a sub-1-μs start-up time, fully integrated 32-MHz relaxation oscillator (ROSC) for intermittent VLSI systems. Our proposed ROSC employs current mode architecture that is different from conventional voltage mode architecture. This enables compact and fast switching speed to be achieved. The measurement results demonstrated that the ROSC achieved sub-1-μs start-up time and generated stable output frequency of 32.6 MHz. Measured line regulation, temperature coefficient, and variation coefficient in 10 samples were ±0.69, ±0.38, and 0.62%, respectively.